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Les dfagrammas suivants lllustrant la mAthoda. 1 2 3 1 2 3 4 5 6 VOLCANOES OF NORTH AMERICA •:!M^° VOLCANOKS OK NOIMH AMKKlt'A. li.il Kii IL'II 1 1 II I t dll x,^ I I'l -'^'jr/r'?'9i Sketch iiiiip of 111,' \v(irl(i slunviiiu' L'cni'riil ilistrihiitidii (if \ uloaiiocs CAfti-r J \ Mh: \\c-r^s ni- H ; ' I ' h > rrf"'~ VOr.CAN'OES OF NOHTIF AMKKH'A. 40 ^^.;^-^ ^u:^:^^^"^-• ^•^ c; /~^r\ - , c^-^ • ■ "^/^»^ iV--. u TRUPICOFCAPRIC •SlifCliCCIPClI 70 ^ i. 1 ri-VTrr7%&^.i^r.-5o I.IM ISO lou I'JU low l-'U 111) Sketch map of tlic world showing' ycnoral (listrilmtiun of volciinoes. f After .foscpli I'lcsiu ich.' (VolLll'.i.l»Ctt /' lUU I'^U 111) lOll \, s of Xorili Aiiicricii sliowii on l*liit(! i.) Ill 1 ' \ Si i| . i; . ;l < >• ' i.'i V r .r ' / ,» A AC 1 I \ 1, A N \ «>:■,'• v\oi: li .ti -!•,<■ I )i\ .>*(f« *" I ■ «i fKJ^' '^v^45^^sv. ^J '. /' VOLCANOES OF NORTH AMERICA A READINa LESSON FOR STUDENTS OF GEoaUAFIIY AND GEOLOGY BY ISRAEL C. lU'SSELL PROKESSOH (II- (lEOLOOV, UNIVKRSITY OF MKHIOVN Al'THOK <.F "r.AKI.S UK N„RTH AMK1M..V," "OLACIEKS OF NdKXH AMKHICA," KTC. THE MACiMILLAN COMPANY LONDON: MACMILLAN & CO., Ltd. 1897 AH rights renerred Q r ^, o ^ R / Cor'VHKJHT, IS'.lT. Bv THE MACMILLAX tuMl'AXY. Nortnaotr \9xtiB J. 9. Cushinjt & Co. - Berwick St Smith Norwood Mais. U.S.A. / INTRODUCTION In the present volume the Western Hemisphere is considered as being divided into two portions ; namely, North and South America. Central America is included in the northern division for the reason that the student of vulcanic phenomena finds a break in the volcanic belts which follow the western borders of the two con- tinents, at the Isthnms of Darien. The series of active and recently extinct volcanoes foniiing the major part of the "Windward islands, sepa- rating; tlie Caribljean Sea from the Atlantic, will not be considered, as it is most intimately associated with the geography and geologj' of South America. Although Iceland is more closely connected geographically with America than w^ith Europe, its political association wdth the Old World, and the fact that it has frequently been described by European travellers, make it convenient to omit it from the present discussion. Among the leading physical features of the southern prolongation of the North American continent compris- ing Mexico and the Central American republics, are numerous still steaming and recently extinct volcanoes, some of which have had their birth since the Spanish conquest. This region also furnishes examples of violent volcanic eruptions, one of which is probably second, in 168787 VI INTUODrCTIOX reference to intensity, among similar events witnessed by civilized man. Many phases of volcanic phenomena occur in the west- ern portion of the United States. The lofty volcanic moun- tains of northern California, Oregon, and Washington are among the most beautiful examples (jf their class to be found in the world. To the eastward of these giant peaks, whose fiery glow has been replaced by the sheen of snow-fields and glaciers, lies a vast lava-covered re- gion, the only known parallel of which, in the extent and thickness of the once molten rocks, occurs in north- western India. In Alaska volcanic energy is still active, and more than a score of volcanoes have been in eruption since the voyages of Bering in 1725-30. It is the character and history of this vast volcanic belt, reaching from the tropical shores of Costa Rica to the western extremity of the bleak and inhospitable Aleu- tian islands, that the attention of students of geology and geography is here invited. The object of this book is to make clear the princi- pal features of volcanoes in general, and to place in the hands of students a concise account of the leading facts thus far discovered, concerning the physical features of North America which can be traced directly to the in- fluence of volcanic action. It is hoped that the accounts of volcanic eruptions here brought together and the discussions of the accom- panying topographic changes, will lead the reader to con- sult some of the numerous books to which reference is l.TKODUCTION Vll Bcl 3t- 11- i-e je It n a. it 1- e e made, aiul thus oljtain, in many instances, more detailed information than it is practicable to include in a bo«)k of the character of the one here presented. While the facts described and discussed in the following paces were derived in many instances from personal observation, much is of necessity compiled from the writings of otlier.s. In all cases, I think, acknowledgments are made of the sources from which information has been borrowed. The numerous foot-notes inserted will ena- ble the reader to verify the accuracy of those portions of the book which are essentially compilations. ISEAEL C. EUSSELL. University of Michioax, May 25, 1897. f CONTENTS IXTIIODUCTIOX rA(ii' v-vii CIIAITKH I CHARACTERISTICS OF VOLCANOES Tyi'KS ok Voi.caxoks: Stromboli; Vesuviiis; Krakatoa; Hawaiian islands; fissure eruptions; Deccau trap; Coluuihia lava; trap r .;ks of the Newark system \-\o Stacks ix thk Livks ok Volcanoes j.')-ls C'liAHACTKuisTics OK THK PRODUCTS OK VoF.cAxoKs : Gaseous and sublimed products ; lii[uid and solid products; lava streams ; tun- nels in lava; aa; pahoehoe; scoriaceous surfaces of lava streams; characteristics of the bottoms of lava streams ; crystalline struct- ure of the central portions of lava sheets ; frag-mental products ; driblet cones ; Pele's hair; bond)s; scoria cones; sheets of volcanic sand and dust 48-80 Pkokilks of Volcanic ^Mountains 80-.s:5 Structcre of Volcanic Moi-ntaixs: Cones formed of projectiles; composite cones ; dikes; volcanic necks . Erosion of Volcanic Mountains 8:}-9() 80-94 Subterranean Intrusions: Dikes; sheets; plugs; laccolites; sub- tuberant mountains ; generalizations !»4-l()(} Characteristics of Igneous Rocks : Classification of igneous rocks based on physical characters, — on chemical characters, — on min- eralogical characters ; granite ; basalt ; rhyolite ; trachyte ; ande- site ; summary .... 106-120 CHAPTER IT General Distribution of the Active and Recently Extinct Volcanoes of North America 127-133 ix CONTENTS CHAPTER III Voi.CAXOEs OF Ckntual Amkiuca: (leneral geology; Panama; list of Central American volcanoes l:J4-l;J!) Yorxd Voi.cANoK.s : Izaico; birth of a volcano in Laiie Tlopanp^o; a nameless volcano in Nicaragua ; Jorullo, Mexico . . 1;J!>-1.')0 Oi.DKR VoLcAXOKs: Consegiiliia ; Volcan del Fuego; Volcan de Agua 15G-171 CHAPTER IV Voiaaxoes of Mf.xico: Orizaba; Popocatepetl; Ixtaccihuatl ; Xinan- tecall ; Tuxtla; Cofre de Perote ; C'olima; volcanoes of northern Mexico; volcanoes of Lower California 172-190 CHAPTER V VoLCAXOKS OF THE United States : San Francisco Mountain, Ari- zona; Mt. Taylor, New Mexico; Ice Spring craters, Utah; Taber- nacle crater, Utah ; craters near Kagtown, Nevada ; Mono valley, California; Mono craters; Mt. Shasta, California; Cinder cone, near Lassen's Peak, California ; Crater Lake, Oregon . . 191-233 The Great Volcaxic Moi xtaixs of Ouegon and Washington; Mt. Pitt ; Three Sisters and Mt. Jefferson ; Mt. Hood ; Mt. Adams ; Mt. St. Helen's; Mt. Rainier (Tacoraa); Mt. Baker . . 233-246 Cascade Mountains 24G-2.50 CoLUMhiA Lava 250-257 Volcanoes of the Coast Raxoe 257 VoLCAxoEs of the Rocky MOUNTAIN Regiox ; Blackfoot basin, Idaho ; Colorado ; Spanish peaks ; New Mexico ; Canada . 257-267 Volcanoes of Alaska: The Aleutian volcanic belt; Cook's Inlet; Redoute ; St. Augustine ; Unimak Island ; Bogosloff Island ; Una- laska Island ; central and western Aleutian islands; summary, 267-283 CHAPTER VI Deposits of Volcanic Dust : Distribution ; physical and chemical proper- ties ; economic importance ....... 284—296 CONTKNTS XI CIIAITKK VII TiiEOKKTiCAL CoNsiDFRATioxs : Interior lifiat of the earth ; physical conditions of the earth's interior; intrnsivo rocks; relation itetween intrnsive rocks and volcanoes; source of the steam of volcanoes; source of the heat of volcanoes; source of the pressure which causes nioUen lava to rise in fissures in the earth's crust ; differ- ences in lavas ; independence of neighboring volcanoes ; origin of fractures in the earth's crust; association of volcanoes with the sea ; influence of water on volca -ic eruptions . . . . 'J07-:U!) Otiikr IIyi'otiiksks: Chemical hypothesis; mechanical hypothesis; steum hypotheses ;31!>-:L'4 CIIAITKU VIII LiKK IIlSTOKY OF A Voj.CANO . ;j27-;i;{.s iXDKX ;):{!) fmmvp^mm; I i I r ILLUSTRATIONS I'LATK 1. <'t, Alaska, 1895 I 8. !t. 10. 11. l-J. i;i. 14. V). HI PLATES KAfE PAliK Sketcli map of the world, sliowinj,' distrilmtion of volcanoes, Fmnthpkcn A'esiiviiis ill (■ruptioii, 1872 g */. l-'iisiyaiiia, .Japan /'. St. An>,Mistine, Cook's Inl< Skf'tch ihap of North America, showing distrihution of volcanoes, 128 Izalco, San Salvador, 1804 .... (I. San Franci.sco Monntain, Arizona | h. Volcanic neck near Mt. Taylor, New Mexico S Ice Spring craters, Utah . Map of ^lono craters, California Mt. Shasta, California n. General view of Cinder cono, near Lassen' h. Section of Cinder cone Geological map of Cinder cone region, California . 14l> lf»4 2(10 •-'16 224 228 2;i0 2:50 2:58 244 270 280 xiii XIV ILLUSTltATION'a riGLKKS 1. Stroiiiboli 2. Profiles of volciiiiie iiiountuiii.> .... :{. Kxpuriment illiiMtrutiuy the Mtructiire of a cinder cone 4. Itleal section tlirougii Vesnvius .... f). DiiiB on tiie shore of Lake Superior 0. Si acciiiiiulatioii of tlic hardened lava about tlic ori)j,'inal (»|»(']dii,u', and now leads to near tlie siinimit of the island. The eon(hiit is still lilled with niobcn lava derived from an unUnown source, |>rol»ably thousands of feet beneath (he llooi' of the iMediturraiiean, and from time to lime oveillows, or exi)losions blow out fra;j,'ments of plastic! rock, and additions of fresh material are made t(< Hie pile. The position of the ()penin<^, through which molten rock, accompanied ))y great volumes of sieam. escapes, is chan^u'ed from time to tinu!, although historical records that such is the case appear to be indelinite, and is now on the northwest side of the mountain, about one thou- sand feet bi'low the summit. This opening is a cup-shaped depre.ssion. or crater. From it a Hat slope, Itoundetl on each side )»y steep cliffs, and known as the Sciarra, de- scends at an angle of al)ont 35° to the sea. This steep slope, however, is a peculiar feature of Strondndi, and not cliaracteristic of volcanoes in general. The study of v(d(!anoes has shown that they may, for convenience, be divided into two ela.sses — the t'xplo.sirc and the fjaid — with reference to the violence (d" their erup- tions. Strond)oli is an exampU; of the former class, but is usually in a nuld state of activity, and thus favoral)le for observing the characteristics of volcanic eruptions. The nature of the eruptions usually in progress at Stroud)oli has been graphically described ))y Judd,^ who visited the island in April, 1874, as follows : * J. W. Jiuld. "Volcanoes," luternntiondl Srienti/ic .S^r/V.f. Apjileton Ik Co., ISSI, This book is recommended to students. From it much of the information presented in tlie present volume concerning the characteristics of volcanoes lias been either directly or indirectly obtained. I I hi ' i I 4 VOLCANOES OF NORTH AMEUICA '" Oil reaching n point upon the side of the Sciarra, from wliieii tlie crater was in full view before me, I wit- nessed and made a sketch of an outbrealv which took place. [Tiiis sketch is reproduced in Fig. 1.] Before the outburst, numerous light curling wreaths of vapor were seen ascendimr from fissures on the sides and bottom of the crnter. Suddenly, and without the slightest warning, a sound was hearci like that produced when a locomotive blows off its steam ; a great volume of watery vapor was Fig. 1. The crater of Stromboli as viewed from the side of the Seiarra during an eruption on the morning of April 24, 1874. (After J. W. Judd.) at the same time thrown violently into the atmosphere, and with i^ there were hurled upwards a number of dark fragments, which rose to a height of 400 or 500 feet above tlie crater, describing curves in their course, and then falling l)ack upon the mountain. Most of the frag- ments tumbled into the crater with a loud, rattling noise, but some of them fell outside the crater, and a fev/ rolled down the steep slope of the Sciarra into the sea. Some of these fallim»: fragments were found to be still hot and glowing, and in a semi-molten condition, so that they j V! CIIARACTEllISTICS OF VOLCAXOES readily received the impression of a coin thrust into tlieni." From ahove the crater, wlien the direction of the wind is favorable, one can look down into the fiery caldroii and learn more of the nature of the eruptions that take place. From such a point of view, as described by Judd, '• The black, slaggy ]x)ttom of the crater is seen to be traversed by many Assures or cracks, from most of which curhng jets of vapor issue quietly, and gradually mingle with and disappear in the atmosphere. But besides these smaller cracks at the bottom of the crater, several larger openings are seen, Avhich vary in number and position at different periods ; sometimes only one of these apertures is visible, at other times as many as six or seven, and the phenomena presented at these larger apertures are especially worthy of careful investigation. " These larger openings, if we study the nature of the action taking place at them, may be divided into three classes. From those of the first class, steam is emitted with loud, snorting puffs, like those produced by a loco- motive engine, but far less regular and rhythmical in their succession. In the second class of apertui'es masses of molten material are seen welling out, and, if the position of the aperture be favorable, flowing outside the crater ; from this liquid molten mass steam is seen to escape, sometimes in considerable quantities. The open- ings of the third class present still more interesting ap- pearances. Within the walls of the apertures a viscid or semi-liquid substance is seen slowly heaving up and down. As we watch the seething mass, the agitation within is observed to increase gradually, and at last a gigantic bubble is formed which violently bursts, when 6 VOLCANOES OF NOIITH AMKUICA a great rush of steam takes place, carrying fragments of the scum-like surface of the liquid high into the atmosphere. " If we visit the crater by night, the appearances pre- sented are found to be still more striking and suggestive. The smaller cracks and larger openings glow with a ruddy light. The liquid matter is seen to be red-hot or even white-hot, while the scum or crust which forms upon it is of a dull red color. Every time a bubble bursts and the crust is broken up by the escape of steam, a fresh, glowing surface of the incandescent material is exposed. If at these moments we look up at the vapor cloud covering the mountain, we shall at once understand the cause of the singular appearances presented by Stromboli when viewed from a distance at ni^^ht, for the great masses of vapor are seen to be lit up with a vivid, ruddy glow, like that produced when an engine driver opens the door of the furnace and illuminates the stream of vapor issuing from the funnel of his locomotive." The bursting of great bubbles of steam on the surface of the viscid lava within the crater accounts for the globular, fleece-like masses of vapor that give a special feature to the steam cloud seen above Stromboli. Similar concentric masses of vapor are a characteristic portion of the vapor columns that rise from many volcanoes during calm weather. An essential element, at least of the less violent eruptions of volcanoes, is thus .shown to be the breaking of huge bubbles of steam. The fact of special significance to be noted in the account of a mildly explosive volcanic eruption just cited, is that the throat of the volcano is filled with molten rock, por- tions of which are violently ejected from time to time by n CHARACTERISTICS OF VOLCANOES the e?cape of steam which rises through the liquid lava. These fragments of semi-m(jlten rock are hurled into the air and fall in part about the opening from which they were ejected, and build up a rim about it. A conical pile of this nature with an opening in its summit, is termed a cinder cone. We also note that sometimes the molten rock overflows the crater and descends the moun- tain as a lava stream. These features, as will be seen later, are characteristic of the eruptions of many volcanoes. Althci^gh Stromboli is usually in a state of mild ac- tivity, yet occasionally the violence of its explosions is greatly increased. The roar of the escaping steam may then be heard for many miles ; fragments of plastic rock are hurled thousands of feet into the atmosphere, and scattered not only over the entire island, but fall in the surrounding waters ; and streams of molten rock flow down from the crater into the sea. Vesuvius. — This world-famed volcano, situated near the shore of the Bay of Naples and about ten miles east- ward of the city of Naples, is a charming and most beauti- ful object wdien beheld from afar. The first evidence of its presence that usually meets the gaze of the expectant traveller, whether approaching over the blue sea or through the picturesque land, is a vast column of steam, rising tranquilly far above the mountain's summit, and then expanding into a broad, vapory canopy. When the wind is not too strong, the cloud is seen to be made up of concentric, fleecy masses, each one of which, as in the case of the cloud above Stromboli, is due to the explosion of a great steam bubble in the caldron of molten rock from which it rose. The vertical shaft of steam with its expanded summit resembles in general form the outlines 8 VOLCANOES OF NORTH AMEllICA of the characteristic stone pine of Italy, and for this reason is widely known as the ^^me tree of Vesuvius. Vesuvius is a conical mountain about 4000 feet high. From the Bay of Naples the steep conical summit is seen to rise within the truncated and half-destroyed crater of an older and much larger volcano, the highest portion of which has an elevation cf 3730 feet. The portion of the rim of the older crater still remaining is termed Mt. Somma. Previous to the Christian era, Vesuvius was familiar to the Romans as a conical mountain with a truncated summit, in which there was a deep depression some three miles in diameter. From the earliest historic times to the year 79, the volcano was dormant and its crater cold and overgrown with vegetation. In the year mentioned, an explosion of remarkable violence occurred, which blew away a large portion of the ancient crater and buried Pompeii and Herculaneum beneath the fragmental prod- ucts that were ejected. It was during this eruption that Pliny lost his life, while iTxaking observations on the earliest volcanic explosion of which history retains a definite record.^ A portion of the wall of the ancient crater, referred to above as Mt. Somma, was left, and within its embrace the modern Vesuvius has been built. The volcano, which gives a matchless charm to a thousand picturesque vistas in the vicinity of Naples, has, like Stromboli, its periods of mild activity, inter- rupted at irregular intervals by explosive eruptions of great violence, which, in many instances, are accompanied ^ This tragic event was minutely and graphically recorded by Gains Plinius, the younger Pliny. A translation of this account may be found in Shaler's " Aspects of the Earth." New York, 1889, pp. 50-56. irti ^^ ■-:^.-:^-.^:l '■■,- ....J>..- . f^- SJWjWfffife'. ^- VOLCANOES OF NC^RTII AMKRK'A. PLATK '.». Fic. A. Vesuvius in eruption. As seen from Naples. .'? p.m., April '2(!, 1S72. Fig. B. Vesuvius in eruption. As seen from Naples, 3.?'J p.m., April 2«, 1872. mi CHARACTEIUSTICS OF VOLCANOES 9 hy overflows of lava. Unlike Stromlmli, however, the variations in its activity are strongly prononnced. At times Vesuvius is dormant for many years and even for centuries, and again awalens to an activity of such energy that southern Italy is shaken hy eartlK|uakos, steam escapes in explosions so violent as to hurl stone and dust high m the air, and even hlow away and dis- trihute far and wide over the adjacent region the material previously forming the summit of the mountain. While Stromboli since the dawn of history has been in a state of mild activity, interrupted at long intervals by explosions of greater violence, Vesuvius has been alternately dormant and its summit cold, and again an object of dread which has brought destruction and death to the fair land sur- rounding it. These two volcanoes belong to the explosive type, as the student will appreciate more fully in advance, but illustrate two quite well marked phases of that type, which have been recognized also in many other volcanoes, and are termed the Stromholian stage and the Vesuvian stage, — the former characterized by long-continued but mild activity, the second by periods of rest bvoken by explosions of extreme violence. When Vesuvius is in a mild state of activity, approach- ing that normal to Stromboli, one may safely climb to the edge of the great bowl which usually exists at the summit and even descend into it, and observe the nature of the molten rock that rises from below, the manner in which the steam escapes from its enclosing magma, etc. In November, 1879, I climbed the cone composed of loose fragments of lava, forming the summit portion of Vesuvius, and reached the rim of the bowl-shaped depres- sion at the summit. The crater near the summit then 1 1 10 VOLCANOKS OF NOKTIf AMKItICA ! t I had an outer slope of al)oiit 35° ; tlie inner slope was more precipitous, Jind exposed the edges of out\vard-dij)[)ing layers of fragmental material, showing that the opening had not long previously been enlarged by tiie l)lowing away of the iuner portion of its rim. This occurred periiaps during the energetic eruption of 1872. Tlie crater was by eye measurement 150 to 200 feet deep, and a thousand feet in diameter. It was floored with black, slag-like lava. The lava in many places was wrinkled or corrugated, owing to slow movement before cooling, and intersected by numerous fissures through which the glow- ing, red-hot rocks beneath could be plainly seen. From some of the fissures, steam was escaping with a hissing noise. In the central portion of the floor of hardened lava, and resting on it, was a rough, conical pile of slag- like lava, rising to a height nearly as great as the highest point on the encircling rim. This inner pile was the cone of eruption. From its summit great volumes of vapor were rolling out, accompanied by puffs which sent globular masses of steam high in the air. With each puff, stones four or five inches in diameter and highly heated, were hurled to a height of between one and two hundred feet in the air. Some of the stones fell on the sides of the conical pile, and occasionally one would roll to its base. At each explosion the entire crater vibrated, but not sufficiently to be at all alarming. I descended to the floor of the crater, and could walk with safety over the recently congealed lava, although it was hot to the feet. One could easily thrust a walking-stick through the crevices and into the still semi-molten lava beneath. On gaining the base of the cone of eruption, I clambered about half-way up its rough sides, but, as the wind was m ■-i- CIIAUACTKRISTICa OK VOLCANOES 11 not strong or regular in any ono dirootion, tlio stonos liurltMl into the air at each explosion fell all about the central orifice, while the steam and gases hecanie more and more dense near the sununit. The pulsating and rumbling of the molten material within the crater could be distinctly heard, and the trembling of the rocks at each explosion when a belch of steam (jccurred, made it troublesome to stand erect. Although prevented from seeing the actual boiling of the lava within the crater, this omission can be supplied by observations made by N. S. Shaler,^ i)i the winter of 1882 : " Taking advantage of a strong gale from the north, the well-known tramontana of Italy, it was possible to creep up to the very edge of the crater and look down upon the surface of the boiling lava, from which the gases were breaking forth. Although the pit was Tiom time to time filled with whirling vapor, the favoring wind often swept it away so that for a few seconds it was possible to see every feature of the terrifying scene. Several times a minute the surface of the tossed lava was rent by a violent explosion of gases, which appeared to hurl the whole mass of fluid rock into the air. The ascending column of vapor and lava fragments rose as a shaft to a height of several hundred feet. Many of the masses, which seemed to rise with the ease of bubbles, were some feet in diameter, and made a great din as they crushed down upon the surface on the southward side of the crater. They often could be seen to fly into frag- ments as they ascended. At the moment of the explosion the escaping gases appeared transparent, a few score feet above the point of escape the ejected column became of a 1 " Aspects of the Earth." New York, 1889. pp. 62-64. /^' 12 VOLCANOES OK NOUTir AMKUICA il; V -I • I': I' stool-gray color, and a litth; liigluM' it chanjjiod to tlio (!liaractoi'isti(3 Imo of stoain. That it was steam sli<^litly mixed with other j^asos was evidcMit whenever in its whirling movements the vaporous column swept around t)\G point of ohservation. The curious '• work-day odor " of steam was perfectly ai)parent, togetlier with the pungent sense of sidphurous fumes suggestive of an infernal laundry. " Although the heat at the moment of explosion was great, it was possible, with the shelter to the face secured by an extemporized mask, to avoid any serious conse- quences from it, and even to make some rather rude and unsatisfactory diagrams of the scene. The principal ob- stacle to observation arose from the violence of the shocks given to the cone and propagated through the air by tlie explosions, which made it extremely difficult to fix the attention on the phenomena. . . . "As if to complete the illustration of volcanic phenom- ena which this little outbreak afforded, there was a small rivulet of lava pouring from the low wall of cinders on one side of the cone and flowing quietly down the slope. It was not much larger than the stream of liquid iron which flows from an iron-furnace to the moulds which await it, but in the motion all the essential features of the greatest of these fiery torrents could be seen. The surface of the fluid, cooled in the air, slowly hardened into a viscid scum. This scum, urged forward by the swifter movement of the more fluid matter below, was wrinkled as is the cream on a pan of milk when it is slowly poured over the edge of the vessel." Two of the most important phases of volcanic eruptions are illustrated by the observations just cited ; one the CIIAUALTKKISTICS OF VOLCANOKS 13 l)l()wiiig out of rock fra,L!,iiit'iit.s by .stoam (.'X[)lu.sion.s, tlu; otlicr tlie ovL'illow of moltuii rock. Tlioso are the cliiof inaiiil'estatioiis, with tlio uxcuptiou of tlio c.scai)e of vast volimios of steaiii, tliat attract the attention in all volcanic oniptions, and may occur .separately or be united in the same outbreak. The mild ex[)lo.sions and rivulet.s of lava characteristic of the eruptions of Stromboli and of the more subdued phases of Vesuvins when in action, have but to be in- creased in intensity and vohunc, to enable one to ai)pre- ciate the nature of even the most stupendous volcanic outbreak that the world has ever witnessed. The proxi- mate cause of the ex[dosions in the eruptions described aljove is plainly the expansive energy of steam. The ori- gin of the steam, the cause of the i)ressure on the molten rock which forces it npward, and the source of the heat that licpiefies the hiva, will be considered in advance. Vesuvius, as already stated, was dormant from its first mention in history until the year 79 of the Christian era. Its grandest eruptions probably occurred in prehistoric times, since the ancient crater, of which Mt. Sonmia is a remnant, was of far greater magnitude than the modern Vesuvius. By restoring the curve of the portion of the ancient crater wall wliich remains, it may be shown that the Somma crater was fully three miles in diameter, and probably more lofty than the summit of the modern cone within it. The duration of the last prehistoric period of quiescence is unknown, but probably embraced several thousand years, since the floor of the crater was cold and solid, and overgrown with vegetation, previous to the eruption of 79. It was in this natural fortress that Spartacus and his band of gladiators took refuge. 14 VOU'ANOKS UK Nouril AMKUICA I I ifj, l( !' I Souk; of tlio fcatiiros of tli«' <^ro;vt eruption of 7'.) are ruconlt'd in tlio acooiml i^ivcn \)y tiu; }'oiin<;(!r Pliny iilruady niforrud to. lie HtJitos tiiat Wis uiH^h! " was at iMisenuiii [on tlic west Hidu of tlio Hay of Naplo.s, about twonty uiiit's in a direct lino from Vesuvius] and was in couiniand of the fleet there. It was at one o'elock in the afternoon oi the 24th of Au yard bctwoeu liis uiuilo's hoiiso and tlio soa], tlio .s[)acL' was mo Hiiiall that tli(! daii^^^or of a catastropli'j from falliii"^ walls wa.s gruat and (HTtain. Not till tlicn Batavia and other points more than a hundred miles from the scene of the outbreak. It became known to the in- habitants of Java and Sumatra that an erui)tion of marked violence was in progress on the island of Krakatoa, but it was not until Sunday, August 26, that the demoi»strations became alarming. A little after noon on that day, a rumbling noise, accompanied by short, feeble reports, was heard at Batavia, 100 miles east of Krakatoa, and at other localities equally distant. Those sounds increased during the night, and at seven the next nioining there came the most appalling crash of all. The sky over the Strait of Sunda and the bordering coasts became darkened by the vapor and dust blew into the air, and the dark- ness increased until the blackness of midnight ensued. Showers of dust began to fall. Repeated earthquakes occurred, and loud explosions, like the discharge of heavy guns, were heard the almost incredible distance of 2267 miles from the scene of action. One of the nearest witnesses of the eruption was Captain Watson, commander of the British vessel, Charles Bal, which was ten miles south of the island of Krakatoa on the Sunday afternoon when the volcano entered on its greatest series of paroxysms. The island was shrouded in a vast black cloud, and sounds like the discharge of heavy guns were heard at intervals of a second of time, and accompanied by a crackling noise thought to have been due to the colliding of rock fragments in the air. A rain of pumice, the larger pieces still quite warm, fell on the ship. It has been estimated that the column of steam, dust, and lapilli that rose above Krakatoa, corresponding with the pine tree of Vesuvius, attained a height of from J.^- CIIAKACTEUISTICS OF VOLCANOES 25 twelve to s(3vcntecn miles, and by 8ome observers was estimated to liave been twenty-tbree miles in altitude. From its widely expanded summit a rain of dust, lapilli, and fragments of i)umice descended on tbe sea and islands over a radius of scores of miles. Tbe finer particles blown into tbe u})per regions of tbe atmospbere were borne away by air currents and finally distributed over tbe surface of tbe entire eartb. Tbe vast quantities of fine dust blown into tbe upper regions of tbe atmospbere caused tbe magnificent sunset and sunrise effects tbat were witnessed on every continent for two or tbree years after tbe eruption. Observers wlio saw tbe magnificent spectacle from a distance describe tbe towering column of steam, dust, and lapilli, as being momentarily illuminated by ligbt- ning fiasbes. Tbe tbunder tbat followed tbese discbarges was lost in tbe roar produced by tbe escaping steam. At niglit, tbe canopy illuminated by tbe ligbt of tbe volcano " resembled a blood-red curtain witb edges of all sbades of yellow ; the whole of a murky tinge, through which gleamed fierce flashes of lightning." The force of the explosion within the crater of Krakatoa was such as to blow away half of the mountain and a large portion of the island on which it stood. At a locality in the central part of the island where a mountain rose previous to the eruption, soundings now show a depth of a thousand feet of water. The geography of the island was thus greatly changed, much of tbe material of which it was composed being blown away. There is no room for doubting that the eruption of Krakatoa was of essentially the same nature as the less violent explosions of Vesuvius and Stromboli. That is, IK 26 VOLCANOES OF NOUTH AMKUICA i, \'' ; If the immediate or proximate cause of the explosion find of all its attending [)henomena was the escape of super- heated steam, or the ignition of gases produced by the disassociaticjn of the elements of water. The suddenness and violence with which the steam escaped may be appre- ciated to some extent, by the general account of the erup- tion given above, but will be better understood by citing more detailed ol)servations. As in all explosions, vibra- tions, or waves, were generated in the surrounding media. In the case of Krakatoa these were of three classes: (1) atmospheric waves, (2) sound waves, and (3) water waves. 1. The atmospheric waves : A large number of bar- ometric observations in various parts of the world have shown thiit the atmospheric wave generated by the great explosion on the morning of August 27 expanded in all directions until it became a great circle, 180° distant from the scene of the explosion, and then contracted to a node at the antipode of its place of origin ; it then ex- panded and travelled back about the earth to Krakatoa ; whence it again started on a journey around the world ; again returning and again expanding and returning, ex- panding outward from its starting-point still again, it travelled half around the earth once more before its ampli- tude became so reduced that it ceased to make a distinct record on self-recording barometers. This remarkable phenomenon of an atmospheric wave travelling about the entire earth -as repeated three and a half times. The time required for each complete excursion around the earth was thirty-six hours and from twenty-five to fifty minutes. 2. The sound wave: Sounds like the discharge of :sv: nrAUACTEUISTICS OF VOLCANOKS 27 heavy guns in f[uick succu.ssiori accoinpaiiiL'd tho eruption of Krakatoa, aiul woru hoard, as ah'oady stated, at phices more than 2000 miles distant. Among the numerons accounts sliowing the immense area over wliieli the sound waves travelled, puhlished i)y the Committee of the Hoyal Society, are the following: At the Port of Acheen, at the northern extrendty of Sumatra, distant 1073 miles, reports like the discharge of cannon at sea were heard, and the troops were put under arms. At Singapore, distant 522 miles, two steamers were despatched to look for the vessel which was supposed to be firing signal guns. At Bangkok, in Siani, distant 1413 miles, the sound was heard ; and also at Labuan, in Borneo, distant 1037 mills. The discharges were also noted at places in the Philip- pine islands, 1450 miles away. The localities just mentioned lie to the northward of Krakatoa. In the opposite direction the noise was heard at Perth, 1092 miles distant, sounding like guns fired at sea, and at Victoria Plains, 1700 miles, in western Aus- tralia ; and Alece Springs, 2233 miles, in southern Australia. In a westerly direction, the sounds were heard at Dutch Bay, Ceylon, 2058 miles ; and at the Chagoz islands, 22G7 mile^. The last named locality is the farthest from Krakatoa at which the sounds were noted. Some idea of the immense distances over which the sound waves travelled may be obtained by a comparison with distances in North America. Had the noise produced by the earthquake that shook Charleston, South Caro- r: 28 VOLCANOES OF NOUTII AMERICA |!i| I I i; lina, August 31, 18SG, Ikumi as ^oud as those wliich accom- paniud tliu explosion of Krakatoa, — and tlie atuiosjilieric and otlier conditions favoring transmission been the same, — it might iiave been iieard at Los Angeles, Cali- fornia, and on the I'rinee Kdward islands. 3. Tile water wave : Tiie eruption at Krakatoa, it will be rememl)ered, occurred on a small island, and was in part subterranean. A shock was transmitted to the water of the sea, which caused it to rise and roll away in great waves. The largest of these sea waves, on reaching the shores of Sumatra and Java, rose to a height of fifty feet above the normal water-level and caused immense losses of life and property.^ The records of self-register- ing tide-gauges in various countries show that the waves thus started travelled at least half around the globe. The brief summary of the character and ' '\»cts of the eraption in the Strait of Sunda will, I 'y, incline the reader to agree with one of our most profound students of volcanic phenomena, who remarks that, while Vesuvius is regarded as a very ol)streperous vol- canic vent, its performances are mere Fourth of July fireworks in comparison with the Day of Judgment proceedings of Krakatoa. If space permitted, a long series of explosive volcanic eruptions might be described, connecting the mild dis- charges of Stromboli, which can be watched with safety at a distance of a few rods, with that of Krakatoa, tlie effects of wliich in one form or another were felt over 1 It is stated by R. D. M. Verbeek, in a report on the eruption of Krakatoa, published by order of the Governor-General of the Xetherland Indies, in 1886, that 3fi,y80 human beings, including 37 Europeans, perished, the greater part of whom were destroyed by the sea waves ; 103 villages were entirely, and 132 partially, destroyed. If a^A'a^ftijiiwn *■»«*« I inww») riiAiiA(rrKiiisTic8 or vou'ANoks 29 it the entire earth. Tlu? oHmoiiiial features in each instance would 1)0 the sanu; ; the strikin;^ (liirtTenees helii*; in the decree of vi(jlence that eharacteri/ed the; eru[>tit»ns. The mild explosions of Stronil)oli and Vesuvius, as we have seen, are duo to the e8ca[)e of the superheated stisani. The same agency (with j)rohal)ly the added etTecits of the ignition of oxygen and hydrog(>n, as will l)e considered later) can he accepted as the immediate or proximate cause of the disastrous explosion in the Strait of Sunda. On a previous page it was stated that volcanoes could ho conveniently divided into two classes, — those that are suhject to explosive eruptions and those which discharge their lavas rpiietly. Let us see what illustrations are availahle of extrusi( is of molten rock froni openings in the earth's crust, which are unaccompanied hy the i)yro- technic displays characteristic of Vesuvius, Etna, S.'intorin, Toneriffe, Cotopaxi, Chimborazo, Conseguina, Jorullo, Ori- zaba, Fusiyama, Sumbawa, and many more — for the vol- canoes of the explosive type far outnumber all others — of the world's most famous volcanoes. Volcanoes of the Hawaiian Islands. — With the excep- tion of small deposits of coral sand, etc., the Hawaiian islands are composed of rocks that were poured out in a molten condition from the earth's interior and piled up during successive eruptions, until the highest summit reached an elevation of nearly 14,000 feet above the sea. The islajids rise from a deep sea. The base of the volcanic pile on the sea-floor is from 15,000 to 18,000 feet below the ocean's surface. Could waters of the sea be with- drawn, the greatest of these volcanoes, Mauna Loa, would stand as a mountain fully 30,000 feet high, and / w lp""li I ^ 1'^' M 30 VOLCANOES OF NORTH AMERICA ifil 3' even exceed the elevation of the loftiest summit of the Himalay.a Mountains ahove the present sea level.' The Hawaiian group consists of four larger and four smaller islands. The largest and most eitaterly ot the group, and the only one on which active volcanoes occur, is Hawaii, which is about ninety miles long by seventy miles wide, and has an area of approximately 4000 square miles. One of the most graphic accounts of the Hawaiian volcanoes, and the one best suited to the present discus- sion, is in a published lecture on the " Hawaiian Islands and People " by C. E. Dutton.^ Much of what follows concerning the volcanoes referred to is derived from this interesting pamphlet. On the Island of Hawaii there are four great volcanoes, and many smaller craters which are now dormant. The southern half of the island is occupied by two grand volcanoes, Mauna Loa and Kilauea. The great central pile is Mauna Loa, the monarch among modern volcanoes. No other in the world approaches it in the vastness of its mass or in the magnitude of its eruptive activity. Etna and all its adjuncts are vastly inferior ; while the three great volcanic craes of the Pacific coast of America, — Shasta, Hood, and Rainier, — if melted down and run together into one pile, would still fall much below the volume of the island volcano. 1 Many accounts of the Hawaiian volcanoes have been published ; among those most easily accessible to American students are : " Hawaiian Vol- canoes" by C. E. Dutton, in the U. S. Geological Survey, 4th Annual Report, 1882-S:{; and "Characteristics of Volcanoes" by J. D. Dana, New York, 1890. The latter contains many references to earlier publications. * A lecture delivered at the U. S. National Museum, Feb. 9, ISSl (sepa- rately published), Washington, 1884. :^''. CHAUACTERrSTICS OF VOLCANOES 81 The summit of Mauna Loa is a moderately flat plain five and a half miles long and nearly four miles wide. Within this plain is sunken a pit three miles long, two miles wide, and a thousand feet deep. In the floor of this pit, at certain times, may be seen a lake of red-hot, liquid lava, varying in size from time to time, but occasionally as large as thirty or forty acres. At intervals of fifteen or twenty minutes a column of liquid lava of great brill- iancy is shot upwards, fountain-like, to a height of over five hundred feet, and falls back into the lava lake in a fiery spray. This grand display is sometimes kept up for months, and is generally terminated by an eruption. 'When an outbreak occurs it does not usually take place at the summit, but a fissure suddenly opens in the side of the mountain, out of which a sheet of lava spouts hundreds of feet into the air, and falling, collects into a river of fire half a mile in width. When this occurs, the lava lake in the crater subsides, and a vast cavity is left, into which masses of rock from the sides, previously sup- ported by the liquid lava, break away and are precipitated with great commotion. This river of molten rock rushed at fi'st with great velocity down the side of the mountain. After running some miles it reaches more level ground, when it spreads out in great lakes or fields, and its sur- face becomes blackened as it cools and hardens. These great eruptions take place without explosions such as characterize the outbursts of Vesuvius, but the lava flows quietly out in enormous deluges, running sometimes for months, or even a whole year, with only the least possible signs of explosive action throughout the entire duration of the flow. Rarely are the eruptions accor.ipanied by earthquakes. So mild are the discharges that an observer 82 VOLCANOES OF NORTH AMERICA may stand to the windward of one of the fiery fountains, and so near that the heat will make his face tingle, yet without danger. Usually the outbreaks take place with- out warning, and even without the knowledge of the people in the vicinity, who first become aware of them at night, when the whole heavens are aglow with the reflected light. The great lava streams that flow down the side of Mauna Loa sometimes attain a length of nearly fifty miles, and occasionally enter the sea. The low angle of slope presented by the flanks of the mountain, and its nearly flat summit, are due to the tendency of the sheet of liquid rock to travel far and spread widel}'^ before cool- ing. It is by the successive addition of such sheets that the mountain has been built up. Nothing like the bombs, scoria, lapilli, and ashes, that are piled about the orifices of volcanoes of the explosive type, occur. The molten rock is characterized by its liquidity. It does not retain the occluded steam until a state of extreme tension and ultimate violent explosion is reached. After mighty Mauna Loa, the next most interesting volcano on Hawaii is Kilauea, situated about tw^enty-five miles to the eastward and rising only 4200 feet above the sea. In the moderately flat summit of Kilauea there is a pit or crater, about three and a half miles in length and two and a half miles in width, nearly elliptical in plan and surrounded with cliffs from 300 to 700 feet high. A view of the interior of this crater as it appeared in the summer of 1883 is described by Dutton, as follows : ^ "The object upon which the attention is instantly fixed ■ I ^ " Hawaiian Volcanoes," U. S. Geological Survey, 4th Annual Report, 1882-83, pp. 104, 106. CHARACTERISTICS OF VOLCANOES 88 is a large chaotic pile of rocks situated in the centre of the amphitheatre, rising to a height which by an eye estimate appears to be about 350 to 400 feet. From innumerable places in this mass volumes of steam are pouring forth and borne to the leeward by the trade wind. This pile of lava blocks is really a cone of eruption with a small crater at the top. At one side of its base is an opening in the floor of the main crater, within which one beholds the ruddy glow of boiling lava. From numerous points in the surrounding floor of the vast amphitheatre clouds of steam issue forth and melt away in the steady flow of the wind. The scene within the great basin is desolate and forbidding in the extreme, but upon the summit of the encircling walls, and over the outer slopes of the mountain, there is a wealth of luxuriant tropical vegetation." Descending the crater walls and crossing the floor of recently hardened lava, from which steam is issuing through countless fissures, one may gain the border of the inner basin and look down on the surface of the pool of molten rock that it holds. It is to be remembered that this pool is really the summit of a column of liquid rock which descends for thousands of feet into the earth. Although red hot and molten at the top, the heat increases with the depth. Bubbles of steam are continually rising through the fluid mass and escaping from its surface. As described by Button, this pool is about 480 feet long and a little over 300 feet in width. " Its shape is reni- form, and all about it rise vertical walls fifteen or twenty feet high. "When one first reaches it the probabilities are that the surface of the lake will be coated over with a black solidified crust, showing a in of fire all about its \ 84 VOLCANOES OF NORTH AMERICA II I ■:i » ' 1 edge. At numerous points at the edge of the crust jets of fire are seen shooting upward, throwing up a spray of glowing lava drops and emitting a dull, simmering sound. The heat for the time being is not intense. Now and then a fountain breaks out in the middle of the lake and boils feebly for a few minutes. It then becomes quiet, but only to renew the operation at some other point. Gradually the spurting and fretting at the edge augments. A belch of lava is thrown up here and there to the height of five or six feet and falls back upon the crust. Presently near the edge a cake of the crust cracks off, and one edge of it bending downward descends beneath the lava, and the whole cake disappears, disclosing a naked surface of liquid fire. Again it coats over and turns black. This operation is repeated at other points on the border of the lake. Suddenly a network of cracks shoots through the entire crust. Piece after piece of it turns its edge upward and sinks with a grand commotion, leaving the whole pool a single expanse of liquid lava. The lake surges feebly for a while, but soon comes to rest. The heat is now insupportable, and for a time it is necessary to with- draw from the immediate brink. Gradually the surface darkens with the formation of a new crust, which grows blacker and blacker until the last ray of incandescence disappears. This alternation of the freezing of the surface of the lake and the breaking up and sinking of the crust goes on in a continuous round, with an approach to a regular period of about two hours." For a more extended account of the quiet eruptions characteristic of the Hawaiian volcanoes, I shall, for want of space, be obliged to refer the reader to the highly in- structive reports concerning them already referred to. i'. CHARACTERISTICS OF VOLCANOES 35 To imderstand the proximate cause of the l)oiling of the lakes of molten rock in the summits of the volcanoes of Hawaii, the escape of steam from them, the formation of jets and fountains of fluid lava, etc., it is of interest to recall a homely comparison suggested by Judd. If a tall narrow vessel is filled with porridge or some similar substance of imperfect fluidity, and placed over a fire, the essential features of an eruption of Stromljoli or of the boiling of the fiery lakes of Hawaii may be imitated in miniature. As the temperature of the mass rises, steam is generated within it, and in the efforts of the steam to escape, the substance is set in violent movement. The movements of the mass are partly rotary and partly vertical in their direction; as fresh steam is generated in the mass its surface is gradually raised, while an escape of the steam is immediately followed by a fall of the surface. An up and down movement is tlius maintained, but as the generation of steam goes on faster than it can escape through the viscid mass, there is a constant tendency of the latter to rise toward the mouth of the vessel. At last, if heat continues to be applied to the vessel, the fluid contents will be forced up to its edge and flow over, the steam being suddenly and violently liberated from the bubbles on the surface of the mass, and a consideralde quantity of the material forcibly expelled from the vessel. A stream of lava and the hurling of fragments of liquid or plastic rock into the air, as frequently happens in Stromboli and Vesuvius, or the spouting of fiery spray from the lava lakes of Hawaii, are thus imitated. The reason for the violent escape of bubbles of steam from the surface of boiling mush, or at the top of the conduit of a volcano, is apparent when it is remembered that the 1 86 VOLCANOES OP NORTH AMERICA i'i I ) * ) I source of heat is deep below the surface. Steam is also generated below the surface, but prolmbly at a moderate depth, and is under the pressure of the liquid mass above, and, besides, the viscid consistency of the material tends to prevent the bubbles of steam from rising. But when the pressure is relieved by an overflow or by the bursting of surface bubbles, the steam below has greater freedom of escape, and rushes violently upward. The cause of the explosions that occur in volcanoes of the Vesuvian type, and the spouting of lava fountains in the lava lakes of Hawaii, is the steam and gases contained in the molten material ; the variations in the behavior of the fluid magma in these contrasted instances depend on variations in its consistency. Lavas that are sufficiently heated are fluid, and boil without explosions ; when less highly heated they are cohesive, and boil less freely. Lavas are also of different composition ; some melt more readily than others, and are more fluid at the same tem- perature. Lavas which consolidate quickly on a lowering of temperature stiffen at the surface, and by resisting the expansive force of the steam, which increases as it nears the surface, are ruptured violently and blown to frag- ments, while lava that does not stiffen so readily retains its fluidity and allows the steam to escape quietly. Although it is not difficult to understand the conditions that are immediately associated with volcanic outbursts, the ultimate cause of the heat present, the nature of the force which causes the lava to rise from far below the sur- face, and the sources of the water that furnishes the steam are more obscure phenomena, which will be considered in advance- Fissure Eruptions. — There is good evidence that most i.i CHARACTEIIISTICS OF VOLGA N'OES 87 volcanic eruptions originate along fissures in the earth's crust. The formation of cracks and fissures seems to be the cause of many of the earth([uakes that precede the birth of new volcanoes, and also herald the renewal of activity in vents that have been dormant. The study of faults, fissure veins, etc., has shown that fissures in the rocks are usually irregular and fre(juently intersect, thus admitting of the escape of steam and hiva with greater facility at certain localities than at others. In some instances, too, volcanoes seem to be located where two fissures cross or intersect. An eruption once started tends to keep its conduit open, both on account of the press- ure which causes the magma to rise, and the fusion of the walls with which the ascending lava comes in con- tact ; but when a conduit becomes closed, other openings are frequently formed along the line of the original fis- sure. Tliis is indicated in numerous instances where suc- cessive eruptions have occurred along a w^ell-defined line or narrow belt. A linear arrangement of volcanoes has been recognized in many portions of the earth. An instance uf this nature is illustrated on Plate 8, which represents a group of beautiful lapilli cones, and small lava flows, situated near Mono Lake, California. If this map were extended toward the northwest and southeast, other vol- canoes along the eastern base of the Sierra Nevada would be included, which indicates still more clearly the inti- mate association of eruptions with a belt of compound fractures and faults. Again, the sides of great volcanic mountains, like Etna, are frequently broken by radiating cracks, through which lava escapes with the formation of secondary craters and surface sheets of molten rock. The lava cooling and .^•w 38 VOLCANOES OF NOUTH AMERICA I! J: .1' it " >', hardening, in such fractures, foiins more or less vertical sheets or dikes, which frequently stand in bold relief as weathering progresses. Should the fissures through which molten rock reaches the surface in what may be termed normal volcanic dis- charge, become more widely opened or more numerous, it is evident that the outpouring of lava might occur more generally throughout their length. If the lava was highly liquid, it would spread out over the land in sheets, without building up craters and mountains, as happens when the energy of the confined forces finds relief at a single cir- cumscribed locality. Such an outpouring of liquid rock would perhaps be the culminating phase of a series of volcanic outbreaks of less intensity, but would differ from them in its wider extent and in the character of the topographic changes produced, but not in its essential characteristics. Great inundations of lava of the nature just considered are known to have occurred, and are designated asjissure eruptions. If we imagine quiet eruptions of highly liquid lava, like those that have formed the broad, flat-topped mountains of the Hawaiian islands, to be increased many thousands of times in volume, and to have reached the surface through intersecting fissures having an aggregate length of several hundred miles, the liquid rock spreading in widely extended sheets over the country, filling the val- leys and giving a new topography to the land, we will have what appears to be the most truthful conception of the leading characteristics of fissure eruptions. If, after one great sheet of lava has cooled and hardened, and its surface becomes covered with soil and vegetation, or CHARACTERISTICS OF VOLCANOES 89 occupied in p.art by lakes, and dissected by streams, we imagine tlie lissures to be again opened and to break througli the first formed layer, a second sheet of lava might be spread out over the previous one, covering its eroded surface, and burying the lacustral and other depos- its that had been laid down on it during the interval of repose. Such a conception furnishes a mental picture of what observations show has taken place many times in certain large areas of the earth. No examples of fissure eruptions of the nature outlined above, can be cited as having taken place in historic times, unless some of the great lava flows of Iceland may be con- sidered as comparatively small illustrations of this method of extrusion. At least two series of widely spread lava sheets of ancient date, however, can be shown to have originated in this manner. One of these occurs in the northwestern portion of the United States, and has been named the Columbia lava; the other, of about the same extent, is in India, and is known as the Deccan trap. The Columbia lava covers an area of between 200,000 and 250,000 square miles in Idaho, Oregon, Washington, and northern California, and is composed of numerous sheets, some of which are separated by lacustral sediments of Tertiary age, and has a maximum thickness of over 4000 feet. A summary of what is known concerning this, the greatest of all the volcanic eruptions of North America, will be presented in a succeeding chapter. A counterpart of nearly all its characteristic features occurs in India. The Deccan Trap. — On the west side of the pe ' isula of India there is a region about 200,000 square miles in area, where the surface rocks are basalt. Bombay is r' 40 VOLCANOES OF NOItTII AMEIIICA I situated in the central portion of the western or seaward margin of tliis iuiiiieuHe tract. The Deccan trap dilfcr.s from the Cohuubia lava in age, being older, and belonging to the Cretaceous instead of the Tertiary period. It also differs from the similar area in America, in the fact that the various sheets of which it is compo.sed have been but slightly disturbed from their original horizontal position. The Columbia lava, as will be explained in advance, has been broken throughout extensive areas by many lines of fracture, and the blocks thus produced tilted and their edges upturned so as to form mountain ranges. The Deccan trap, for the most part, has never been covered by later formations, but on account of the great length of time it has been exposed, and also because of the warm and humid climate of India, it has suffered deep decay, and is covered quite generally with a thick layer of residual earth known as laieriie. In the vicinity of Bombay, the Deccan trap has a thickness of over 6000 feet, but thins out gradually eastward. The western portion of the area is covered by the sea, so that its full extent is unknown. In the southern prolongation of the trap area, its thickness is estimated at from 2000 to 2500 feet; in the extreme eastern portion, between 500 and COO miles eastward of Bombay, the thickness in general is but 500 feet. The average thickness for the entire area is thought to be about 2000 feet. The Deccan trap is a dark basalt and consists of many layers, some of which are separated by sheets of lacustral sediment, and by volcanic lapilli and " ashes." Where the rocks beneath the basalt are exposed, they are w- CIIAUACTKUISTIC'S OK VoLCANi HCS 41 found to bo trnverscd by dikes. On tbo surfaco of tbe basalt tliero are no volcanic cones or crat(M's of any de- scription, which can Ije considered as niarkinj^ the; posi- tions of vents from which the lava was extruded. In all of these respects the vast lava-covi'red area of India agrees, ahno.st to the minutest particulars, with the conditions found to exist in the region drained by the Columbia River. The facts just enumerated concerning the Deccan trap have been taken from an admirable ac(!ount of the geology of India, by Oldham.' A summary of the observations made on the trap sheets of India contained in this volume, might be transferred almost bodily to a description of the Columbia lava. On account of this double interest, I take the liberty of introducing it here : "Recapitulating the whole evidence [concerning the Deccan trap], so far as it is presented to us by the obser- vations hitherto made, we find that in times subsequent to the middle cretaceous, a great area of the Indian penin- sula formed part of a land surface, very uneven and broken in parts, but to the eastward apparently chiefly composed of extensive plains, which, by some slight changes of level preceding the volcanic period, were con- verted into lakes. . . . The lakes had apparently been drained, and the deposits, which had accumulated in them, had locally been subject to denudation before the first outburst of lava took place. These occurred at con- siderable intervals, small and very shallow lakes or marshes being formed in the meantime by the interrup- tions to the drainage produced by lava flows, or by ^ R. D. Oldham, "A Manual of the Geology of India," second edition. Calcutta, 1893, pp. 255-289. I v 42 VOLCANOKH OF NOUTH AMKitICA cliangca of level iiocompanying the volcanic eruptions. In these lakes a rich fainia of fish, niolhisca, entomo.stra- coua Crustacea, and water i)lanta existed, whilst a varied and probably a rich vegetation occu|)ied the surrounding country. . . . Fresh flows of lava filled up the first lakes, and covered over the sedimentary deposits which had accumulated in the waters, but these very Hows, by damming up other lines of drainage, produced fresh lakes, so that several alternations of lava and sedimentary beds were produced in places. Gradually the lakes seem to have disai)peared, whether the lava fiows succeeded each other so rapidly that there was no time for the accumula- tion of sediments in the interval, or whether, as is more probable, the surface had been converted into a uniform plain of basalt by the enormous lava streams which had been poured out, it is difficult to say, but no further traces of life have hitherto been found until towards the close of the volcanic epoch. It is possible that at the end, as at the conuuencement of the period, the intervals be- tween eruptions became longer, and the animal and vege- table life, which may have been seriously diminished or altogether driven out of the country during the rule of igneous conditions, resumed its old position, but a great change had taken place in the long interval : the old lacus- trine faima had died out, and the animals and plants which now appeared in the country seem to have differed from those which had formerly occupied it. Lastly, in the northwestern portion of the area, parts of the vol- canic country were depressed beneath the sea, and marine Tertiary deposits began to be formed from the detritus of the extinct volcanoes and their products. A great tract of the volcanic region, however, appears to have remained ! ■ CHAltACTEIUSTIC8 OF VOLCANOES 48 ! tiliiio.st un(li8turl)(!(l to the prcsi'nt day, alToctiMl l)y sul> aerial oro.sion alone, "ud never depr 'sscd hciieath tho sea level, though probably for a time at a lower eleva- tion than at present." A comparison of this aceonnt of the great basaltic sheets of India, with the descrijjtion given hiter, of the similar area in Am(M-ica, will be found instructive. Large porticjus of Ai^yssinia are reported to be covered by surface Hows of lava, similar in many ways to those of India and America, but the evidence available concerning them is not sufficient to show conidusively that they are the result of what is understood as fissure eruptions. In some regions, also, as for example the northwestern part of the British Islands and the adjacent region to the northwest, extending perhaps as far as Iceland, there are extensive systems of dikes, which at one time, there is little doubt, led to extensive surface flows. These erui)- tions were so ancient, however, and the region during its subsequent history so situated in reference to sea level, that erosion has removed all or nearly all of the surface layers, leaving only the truncated dikes that were formed by the filling of the fissures through which the extruded material found its way to the surface.^ Trap Rocks of the Newark System. — In the region occupied by the Newark system, on the Atlantic slope of North America and extending from Nova Scotia to South Carolina, there is one of the most extended series of dikes and sheets of igneous rocks thus far discovered. The length of this series from northeast to northwest is 1 Archibald Geikie, " The Lava-fields of Northwestern Europe," in "Geological Sketches at Home aiid Abroad." New York, 1882, pp. 239- 249. TT 44 VOLCANOES OF NOUTH AMERICA li: about 1000 miles, and its width, although its eastern border is concealed by more recent deposits and by the sea, is not less than 200 miles. The area traversed by these dikes is nearly as great as that occupied by the Deccan trap or the Columbia lava; but unlike the regions where those formations were spread out, the Atlantic coast belt was an area of both sedimentation and deep erosion during and after the igneous invasion. The sheets of lava extruded at the surface became in part buried be- neath subsecpient sedimentary beds, and where erosion has been least, still survive. In the greater portion of the area alonu; the Atlantic coast that was fractured so as to admit of the upward passage of molten rock from beneath, extensive and deep erosion has occurred, and only truncated dikes and remnants of igneous sheets remain. The dikes, in part, traverse rocks of Jura- Trias age, and their truncatcil summits, in certain locali- ties, are buried beneath Cretaceous sediments.^ The several regions referred to above furnish indis- putable evidence that fissures have been formed in the earth's crust, throughout great areas, during widely sepa- rated intervals of geological time, and that through these breaks vast quantities ot molten rock have been out- poured. These, the greatest of all eruptions of \olcanic material that have occurred since the dawn of what may be styled authentic geological history, have in most instances been accompanied by the formation of minor quantities of projectile material, such as lapilli, dust, etc. In the main, the deluges of molten rock occurred without the formation of craters or pronounced elevations of any 1 I. C. Russell, "Correlation Papers — The Newark System." United Statt.^ Geological Survey. Bulletin, No. 85, pp. 06-77. w CHARACTERISTICS OF VOLCANOES 45 kind. The layers occupy depressions and tend to subdue the inequalities in topography produced by previous up- heavals and l)y erosion. The rocks poured out during fissure eruptions are dark, heavy, and, as will be explained in advance, are basic rocks, which fuse at a lower tem- perature than the more siliceous lavas, and when melted are highly fluid and flow rapidly, thus admitting of their expanding broadly into thin sheets. Stages in the Lives of Volcanoes Volcanoes, like many other features of the earth's surface, have their time of birth, periods of activity and decline, terminating at last in a time of repose, wdien they become silent and cold. These changes are less regular and less plainly the result of well-known laws than the similar sequence of events exhibited by other features of the land, and are apt to be considered, in part, at least, as of the nature of catastrophes. Could we take into account, however, all the forces that co-operate during the varying phases of the life history of a volcano, as, for example, the effects accompanying the cooling r •; the earth, the formation of thick layers of sediment charged with sea water, the manner in which surface waters find their way into subterranean regions, etc., it would probably be discovered that even volcanoes which break forth with severe earthquakes, and explode with such violence as to scatter rock fragirents over half a continent, are in reaUty the result of slowly acting and finally culminating forces which obey definite laws. However great the diversity that volcanoes display during their more active stages, there usually comes a 46 VOLCANOES OF NORTH AMERICA I r time in their decadence when they heave marked simi- larities. As their energy declines they pass to a state of feeble activity, during which a moderate amount of heat is given off, accompanied by the escape of steam, carbonic acid, sulphuretted hydrogen, and other gases. The earlier portion of this period of decline, when the rocks are still highly heated and at night appear red hot about the orifices from which steam issues with hissing and even a roaring noise, is termed the fmnarole stage. Volcanoes in this condition emit sulphurous and hydrochloric acids and less quantities of sulphuretted hydrogen and carbonic acid gas. About the orifices when the rocks are sufficiently cool, deposits of ulphide of arsenic, chloride of iron, chloride of ammonium, boracic acid, and sulphur are frequently formed. A more marked decline, known as the solfaiara stage, is characterized by a marked decrease of heat and a less energetic escape of steam. The gases, in fact, as they pass off, are usually little if at all above the mean tem- perature of the atmosphere. The type of volcanoes in the solfatara stage is furnished by Solfatara, near Naples, from which the specific name is derived. From fissures in tiie floor of the crater of Solfatara there issue contin- ually watery vapors, sulphurous acid, sulphuretted hy- drogen, hydrochloric acid, and chloride of ammonium. The action of these substances upon one another, and upon the volcanic rocks through which they pass, gives rise to the formation of certain chemical products which, from a very early period, have been collected on account of their commercial value.^ The rocks surrounding sol- fataras are frequently changed both in color and com- 1 J. W. Judd, " Volcanoes." New York, 1881, pp. 213, 214. CHAKACTEIUSTICS OF VOLCANOES 47 position by the action of the gases that come in contact with them. In the passage from the fumarole to the solfatara stage, the decrease in temperature is accompanied by a change in the nature of the gases emitted. Sulphurous and hydrochloric acids diminish, and the quantity of sulphuretted hydrogen and carbonic acid mingled with them proportionately increases. When nearly all signs of volcanic activity have ceased, carbonic acid continues to pour forth, and being heavier than the air, tends to collect in low places, and forms so-called poison valleys, in which insects and even large animals sometimes perish. These manifestations of ex- piring energy are due mainly to contact of water with the hot rocks, and do not show that a conduit leading to sub- terran-^an reservoirs is still open. Fumaroles and solfa- taras are sometimes found during the early stages of volcanic activity, their energy increasing nntil explosions of steam or eruptions of lava occur ; the eruptions being followed by long periods of decline, as already stated. The characteristics of the youth of volcanoes are thus repeated in what may be termed ; second childhood. A still later phase of volcanic energy, following the solfatai I stage, and when gases no longer escape, is marked by the occurrence of hot springs and geysers. In regions covered with once molten rock, a great lapse of time is required for the heat to be conducted away. One of the processes by which this is accomplished, is by the percolation of rain water through the rocks, and its emergence at the surface as springs. Water passes under- ground for great distances, and also penetrates to a great depth, not usually in open passageways, but by perco- ■) 48 VOLCANOES OF NORTH AMERICA 11 * II II li f ; I * lating through the interstices of the rocks themselves. The residual heat of volcanic beds is thus abstracted and conducted to the surface. Fissures intersecting the rocks aid the escape of the underground waters. Fissure springs thus formed are frequently of great volume, and pour forth with temperatures ranging from that normal to the rocks near the surface up to the boiling point of water, for the elevations where they occur. Not all hot springs owe their temperatures to the re- sidual heat of volcanic rocks, however, since water may penetrate to the subterranean regions that are affected by the general heat of the earth's interior and again reach the surface. The cooling of the earth is greatly assisted in this way. Motion along lines of fracture as where faults are formed, or rocks are folded and wrinkled, may also be transformed into heat by friction, and thus give origin to hot springs that are in no way different, so far as their surface manifestations are concerned, from those originating in other ways. The three geyser regions of the world are in volcanic regions, but while geysers, on account of the source of the heat which is the mainspring of the striking phenomena they display, may be studied in connection with the subject before us, it seems best to defer their consideration and place them in the aqueous rather than the igneous branch of physiography. vl 1 ' Characteristics of the Products of Volcanoes The matter emitted by volcanoes may for convenience be divided in general into two groups ; namely, gases and solids. This is perhaps not a scientific classification, since during eruptions, much of the material included T, CIIAUACTEUISTICS OF VOLCANOES 49 among the solids is poured out in a liquid condition ; and some of the gases and vapors are soon condensed into solids. Gaseous and Sublime 1 Products. — Of all the gaseous or vaporous products discharged by volcanoes, steam is by far the most abundant, and may be considered as the mainspring, but not the ultimate cause, of many volcanic phenomena. No adequate measure of the amount of steam given off during eruptions, even of mild intensity, has been made, but that its volume is immense can readily be appreciated. A visitor to Naples usually has his attention attracted by the "pine tree" of vapor that may almost always be seen in calm weather, towering above the summit of Vesuvius. Observers agree that this column is composed almost entirely of the vapor of water. During all stages in the activity of Vesuvius in recent centuries, this cloud has hung over the mountain, at times rising thou- sands of feet before expanding, and at other times, when the wind is strong, drifting away so as to resemble the cloud banners so frequently to be seen about Alpine summits. Day and night, and year after year, this great volume of steam has been pouring out of the crater, as if it was an immense boiling caldron — which in fact it is. When the activity increases, the steam issues under great pressure and with a roar that can be heard for many miles. The vapor column then becomes vastly enlarged and sometimes, on condensing, causes heavy rainfalls; thus demonstrating, on a grand scale, that it is the vapor of water which makes the mountain an object of dread. It has been computed by Fouque, that one of the numerous parasitic cones on the lava flows of Etna 60 VOLCANOES OF NORTH AMERICA •i emitted sufficient steam during one hundred days to form 402,000,000 gallons of water if condensed. All of the steam emitted by the numerous parasitic cones about that great volcano, however, if combined, would fall far short of the amount that escapes from its central crater. The quantity of steam that escapes from volcanoes after they have passed to the condition of fumaroles and solfa- taras, is still immense. In numerous examples like Sol- fatara and Volcano, steam has been continuously emitted for centuries, with a roar like that produced when an ocean steamer reaches her moorings and the safety valves are opened. Not only Vesuvius and Etna, but probably every other volcano that has been seen in action, emits steam which is derived from subterranean sources. From what is now taking place at hundreds of vents, it is safe to conclude that all the volcanoes that have existed on the earth throughout its geological history have been accompanied by the escape of steam from within the earth's crust. Among the numerous questions which the observation of volcanoes had suggested, one of the most important is whether the steam they emit is derived from water pres- ent in the earth from the time it became a planet, or is the supply furnished by the descent of water from the surface ? It is my intention to leave theoretical discus- sions until the student has made some advance in obser- vation, but the analogy between volcanoes, geysers, and springs, as well as the study of volcanoes themselves, suggests an immediate answer to this query, to the effect that it is surface water which supplies the steam. Of the gases and vapor emitted by volcanoes, it has been estimated that nine hundred and ninety-nine parts in pcgcrarz' CHAUACTEUISTICS OF VOLCANOES 51 a thousand consist of steam. Of the siil)stances given off in a gaseous condition with the steam, the most ahundant is usually sulphurous acid. Chlorine is also present and gives origin to hydrochloric acid ; it is the pungent fumes of this acid which frequently makes a near approach to the crater of Vesuvius impracticahle. Snli)huretted hydrogen is also emitted, and, being inflanunable, some- times burns with a bluish flame. With the exception uf flames of burning hydrogen, noted below, this is nearly always about the only actual burning that accompanies volcanic eruptions, and is of decidedly minor importance as a part of the spectacle witnessed. The idea that a volcano is a " burning mountain " originated from seeing the glow of molten lava which is frequently reflected on the clouds of steam above a crater. Hydrogen has also been found in volcanic gases. From observations made by Siemens, at Vesuvius in 1878, as stated by Geikie,' it was concluded that vast quantities of free hydrogen and of combustible compounds of that gas exist dissolved in the magma of the earth's interior, and that these rising and exploding in the funnels of volcanoes give rise to detonations and clouds of steam. When the source of the water which furnishes the steam of volcanoes is considered, it will be found that it is not necessary to consider that the free hydrogen given off by volcanoes is necessarily derived from the earth's interior, as just stated, as it may arise from the dis.^ociation of descending surface Avater on coming in contact with ascending lavas. At the eruption of Santorin, in 18G6, hydrogen was distinctly recognized by Fouque, who for the first time established the existence of true volcanic 1 Archibald Geikie, "Text-book of Geology," 2d edition, 1885, p. 183. I 52 VOLCANOES OF NORTH AMERICA If I fltiineH. These flames were again studied spectroscopi- cally in the following year by Janssen, who found them to be due principally to the combustion of free hydrogen, but with traces of chlorine, soda, and copper. Fouquc determined hy analysis, that immediately over the focus of eruption, free hydrogen formed thirty per cent of the gases euiitted, but that the proposition rapidly diminished with distance from the active vents and hotter lavas, while at the same time the proportion of marsh gas and carbon dioxide rapidly increased. The gaseous emanations collected by Fouqu(3 were found to contain aljundant free oxygen as well as hydrogen. One analysis gave the following: Caibon dioxide 0.22, oxygen 21.11, nitrogen 21.90, hydrogen 56.70, marsh gas 0.07 = 100.00. This mixture on coming in contact with a burning body at once ignites with a sharp explosion. These observations lead to the inference that the water vapor emitted from volcanic vents exists in a state of dissociation in the molten magma previous to its erup- tion. This conclusion is not o)dy interesting in connection with volcanic studies, but highly suggestive in reference to our concejitions concerning the conditions existing within or below the earth's crust. As already stated, a decrease in volcanic activity is usually accompanied by a change in the gases emitted. This is not only an increase in the percentage of the usually less abundant gases, owing to a decrease in the volume of steam poured out, but a variation in the nature of the gases with changing conditions. The nature of this change is believed to differ, however, in different volcanoes. In the case of Vesuvius, according to Sainte-Claire Deville, the most energetic eruptions are accompanied, by the dis- h>i r ;:rJ ' - ' ::Lti ' -i iM-^J t ^i ^tAm mmmsmsm CHARACTERISTICS OF VOLCANOES r)3 charge of clilorino, and to a loss oxtent, by fluorine ; while sulphurous gases are evolved during periods of lessening energy, being characteristic, in general, of solfataras, while carbonic acid becomes prominent in fumaroles. Of the great variety of substances deposited on Oie cooler rocks in the vicinity of fumaroles and solfataras, the following may be enumerated, but the list is not complete. Sodium chloride (common salt) is sometimes abundant, and in the case of Etna is said to occur in such rpiantities as to be of commercial importance. The whitening of the country about Vesuvius by salt precipi- tated from the air during an eruption has already been noted. The common occurrences of saH in the vapors of volcanoes is one of the arguments sometimes advanced for the purpose of showing that eruptions are due to the access of sea-water to regions where rocks are highly heated. That salt may be derived from other sources, however, will be shown later. Ferric chloride is con- spicuous about many volcanic vents, and coats the rocks with yellow and reddish incrustations that are frequently mistaken for suli)hur. Sulphur also occurs, sometimes in large quantities, and in many localities is of commercial value. Ammonium chloride and boracic acid are among the products of solfataric action that are of economic importance. In addition to the more common substances just named, there are found sodium carbonate, sulphate of lime, specular iron, oxide of copper, and some rock-form- ing minerals.^ Liquid and Solid Products. — All rock material poured out of volcanoes in a highly heated and fluid or plastic ^ For further information concerning the gases ami vapors given out by volcanoes, consult J. W. Judd, "Volcanoes," pp. 40-44. . ir 54 VOLCANOKH OK NOUTH AMKUICA .! I I. I; iK,| ' condition is termed lava, irrespective of its niincralogical or chemical composition. Much of the lava becomes cooled sullieiently, however, before its appearance at the surface, to bo in a solid condition, but is still hot, and from its identity with the liquid lavas that have cooled on the surface is plainly of the same origin. The term lam, in fact, includes all of the solid and molten products of volcanic eruptions, except the fragments sometimes torn off by the volcanoes of the explosive type from the beds through which the extruded material passes in order to reach the surface. The fragments of limestone scattered over the sides of Vesuvius are examples of such non-vol- cauic intrusions in the midst of truly igneous material. Other similar oxami)les will be cited later in connection with a description of the Mono craters, California. The molten material hich rises in the conduit of a volcano, but does not reach the surface, although it may be of the same mineralogical and chemical composition as that which is actually extruded, is not usually termed lava. Rocks formed in this way are called plutonic rocks. Between volcanic rocks or lavas and plutonic rocks, however, there is no well-defined boundary, although more or less marked physical and mineralogi- cal differences result from the conditions under which they cool and harden. These differences will be noted on a subsequent page. Lava Streams. — At times the column of molten rock in the throat or conduit of a volcano rises until the crater to which it leads is filled, and an overflow takes place across the lowest point in the crater's rim. In some instances a stream of lava appears to form a channel for itself by melting the rocks over which it \ CirAUACTKUISTIC'H OK VOLCANOKS 65 flows, hut that tliis is of common oociirronce is doiihtful. When tlio sides of a volcanic mountain are couiposed of llglit, incoherent scoria, hipilli, etc., sucii material may l)c carried away, some of it prol)ahly hcing fused. In this way a crater is souietimes hreaciied, and a [)()rtiou of its rim removed. Again, the pressure of the lava rising within a crater may he sufficient to rupture the walls that confine it. The howl containing the molten rocks is thus hroken and its contents escape. A more connnon way in which craters discharge their hivas is hy the opening of fissures in their sides. The lava is thus drawn olf perhaps at the very hase of a crater, leaving its rim unbroken. The innnense pressure of a column of lava rising within a volcanic mountain greatly favors this mode of escape. In the case of the volcanoes on the Island of Hawaii, the lava sometimes issues from openings on the sides of the mountains and forms innnense fiery fountains, several hundred feet in height, which play for days and even weeks. The immediate force which causes these great jets to rise is the static pressure of the molten rock at higher levels within the mountains. The behavior of a lava stream after starting on its wav down a mountain varies according to its degree of liquid- ity, the stec pness of the slope, the character of the surface over which it flows, etc. At times the material is highly liquid and flows almost like water; again it is thick and viscid and descends slowly even on precipitous slopes. This difference in fluidity is due mainly to variations in the composition of the lava itself, some lavas fusing more readily than others, and also to the degree of heat that affects it. With sufficient heat all known substances 66 VOLCANOES OF NORTH AMEJIICA il II I I il would beconu! fluid, l)iii the do^ree of lioat that will cause certaiu lavas to becoino highly fluid will produce only a viscous condition in others. Lavas may l)c divided into two somowliat well-defined classes, in reference to the amount of silica they contain; namely, basic and aciver, have been made. A great surface flow of lava on Hawaii, in 1852, advanced twenty miles in as many days. Another stream, emitted in 18oU, advanced thirty-three miles in eight days, corresponding to an average rate of four miles a tlay on a mean slope of one foot in fifteen. A stream about thirty miles long, in 1880 and 1881, advanced for nine months, on a mean slope of one foot in thirteen, or about live degrees.^ It needs no argument to show that the rapidity Avith which lava streams flow will depend largely on the slopes of the surfaces they descend, since they nuist obey the laws of dynamics as applied to liquids. Other conditions being the same, the steeper the slope the more rapid will be the flow. The topography of a region over which lava flows also influences the shape of the stream and the rate at which it will advance. For example, if the sides of a volcano are channelled by descending valleys, the lava gathering in such depressions will be confined, thus diminishing radiation and admitting of a quicker and greater ad- vance than if it should spread out on a uniform, uneroded slope. 1 J. D. Dana, « Characteristics of Volcanoes," New York, 1890, pp. 238, 239. I I'l >H v. 'i, (ill I 'i. ti 68 VOLCANOES OF NORTH AMERICA The lava streams of the Hawaiian islands are com- posed of basic lava, and, as already stated, are highly fl'j'd at the time of their extension. Where the descent is somevvhirt precipitous, they flow rapidly, and at first are almost as liquid as water, but on reaching the base of the mountain they expand laterally and flow more slowly, owing in part to a decrease of fluidity due to loss of heat. The length of these streams is sometimes between forty and fifty miles. Acid lavas, on the other hand, are usually thick and viscous, and flow sluggishly even on steep mountain sides. Frequently a stream of acid lava will cool and harden on a slope down which a basic flow would plunge in a cata- ract of fire. The tendency of basic lavas is to spread out in thin sheets, which terminate with low frontal slopes, although a thin margin is by no means the universal rule ; while the tendency of acid flows is to form thick sheets with precipitous, and in some cases, almost overhanging cliff-like margins. Tunnels in Lava. — The conditions controlling the rate of flow of lava streams also influence various phenomena displayed by them as they advance and gradually cool. In the case of highly liquid lavas especially, the surface hardens, while the stiil molten portion beneath flows on. When the flow is rapid, this crust is usually broken before it can reach sufficient thickness to support its own weight, and the cakes of hardened rock either sink and are remelted, or are swept along in confused piles. When the advance is slow, or is checked and starts again when the liquid portion below finds an escape, the hardened surface is left as a roof over the space vacated by the draining away of the molten rock beneath. Caverns of k^. CHARACTERISTICS OF VOLCANOES 5a J this nature are of common occurrence in lava-covered regions, and may sometimes be followed for a mile, or perhaps several miles, although they are frequently obstructed by the falling in of portions of their roofs. Examples of caverns formed in the way just described will be noticed in giving an account of the volcanoes of Utah and California. The descent of heated waters into lava caverns some- times leads to the formation of curious stalactites, which differ, however, from those of limestone caverns. A study of these peculiar forms has been made by Dana^ and others. The Aa Surfaces of Lava Streams. — The hardening or fraezing over of lava streams while the magma beneath is still flowing, leads, as already stated, to the fracturing of the crust and the displacement of the blocks thus formed. Under the proper conditions affecting the rate of cooling and the flow of the still plastic interior of a stream, the surface blocks are carried along, and when the lava finally hardens, are left in a state of utmost confu- sion. Sometimes the blocks are piled in huge heaps, and again the general surface, although nearly horizontal, is composed of cakes of lava inclined in all directions, and is all but impassable. In the Hawaiian islands surfaces of this description occur over areas many square miles in extent, and are known by the native name Aa. This name has been adopted into the technical language of geology, and found to be useful in describing many volcanic regions. 1 E. S. Dana, "Lava Stalactites from Caverns in Mount Loa Lava Streams," in " Characteristics of Volcanoes," by J. U. Dana, 1890, pp. 332- 3i2. wm 60 VOLCANOES OF NOKTII AMERICA ! ! , 1 Hiy * Id;* U T Charactoristic aa surfaros occur on every variety of lava, but aro most pronoiuniod, perhaps, on those ol the acid t3'pe. Wlien the flowing magma is but imperfectly fluid, a slight loss of heat leads to the harden irg of the surface, and the conditions favoring to the formation of aa are soon reached. The surface sheet of frauinents is then thick, and, indeed, in some instances the entire stre M becomes charged with angular rock masses, held in a still viscid magma. Such a stream on solidify- ing forms one variety of what is termed a volcanic breccia.^ The fact that the blocks of lava seen on aa surfaces actually floated on the viscid stream of molten rock flow- ing beneath them is sometimes shown by grooves and striations on their under surfaces. As the blocks are carried along they grind against each other, making a harsh noise. In this respect partially congealed lava streams form a marked contrast to the advance of more liquid lavas, which under similar topographic conditions flow quietly. The formation of aa on Hawaii is thiis described by Button : '^ " Ui)on the mountain slopes the lava runs with great velocity, and the streams are correspondingly nar- row. But when it strikes the nearly horizontal plain below, its velocity is checked, and the liquid accumulates in great volume, becoming viscous by cooling. Its flow- is greatly retarded, and yet the mass is sufficient to en- ' A V)reccia is a rock composed of or containing anf^ular fragments. A sedimentary breccia consists of angular fragments of older rocks of any character cemented together by mud, sand, etc. In cave breccia, angular fragments are united by the deposition of calcium carbonate, etc. '■* C. K. Button, *' Hawaiian Volcanoes," U. .S. Geological Survey, 4th Annual Report, 1882-8;5, p. 157. r. m -ratniyr a x it n .^ CHAUACTEUISTICS OF VOLCANOES 61 fi J '1 able it to move with a slow motion analogous to that of a glacier. Wlion the viscosity of the lava becomes very great, it is in a condition which enables it to yield to strains of a certain amount ; but if that strain is exceeded, it is crushed and ground up. The movement which takes place at this stage is partially a plastic yielding, more par- ticulai'ly of the interior and hotter parts, and partly a shattering and grinding up of the outer, stiffer, and colder parts. This glacier-like motion, however, is possible only with very large masses of the lava, which still retains a sulllcient quantity of heat to maintain a plastic condition. Persons who have witnessed the movement of a clinker field in the last stages of an eruption describe it as be- ing so slow as to be fjuite imperceptible until it has been watched for a long time, and as being attended with a crunching noise which comes in volleys like the report of musketry." The aa surfaces of lava streams resend)le in some respects the surfaces of northern ice flows, where blocks of ice are ground together and forced far up shelving shores by the pressure of the wind and of water cur- rents. Although the surfaces of basaltic lavas are frequently rough, on account of the method of cooling described above, their ruggedness i;. mild in con.i)ar son with the surfaces of some acid lavas, as rhyolitic obsidian, for ex- ample, which is in reality a glass, and breaks witli shar}) points and blade-like «:;i]gL- An exanqile of this nature is furnished by thr streams of obsidian on the sides of the jSIoiio crater, California. An attempt to cross such a field of jagged and angular fragments of glass is peril- ous to life and limbs. I 62 VOLCANOES OF NORTH AMERICA u I il: 1 I! •i '. f )ll! I'i The Pahoehoe Surfaces of Lava Streams. — While the surfaces of tliick sheets of basalt arc l)roken and rendered rough and uneven in the manner already described, thin sheets cool rapidly ^vithout breaking into cakes, but fre- quently become wrinkled, owing to the sluggish flow of the thickening magma. At times these wrinkled and ropy surfaces are smooth, resembling somewhat in ap- pearance the surface of wind-rippled mud, and again they are scoriaceous and rough. These variations depend on the nature of the lava and the conditions under which it cools. These wrinkled surfaces frequently form swelling or oval masses, which overlap and merge with another. To this peculiar and characteristic variety of lava sur- face, the natives of the Hawaiian islands have given the name Pahoehoe. Its appearance is thus described by Button, in the report just cited : ^ " Imagine an army of giants bringing to a common dumping-ground enormous 3aldrons of pitch and turning them upside down, allowing the pitch to run out, some running together, some being poured over preceding dis- cliargcs, and the whole being finally left to solidity. The individuality of each vesselful of pitch might be half pre- served, half obliterated. The svu-face of the entire ac- cumulation would be embossed and rolling, by reason of the multiplicity of the component masses, but each mass by itself would be slightly wrinkled, yet, on the whole, smooth, involving no further impediment to progress over it than going up and down the smooth-surfaced hummocks." As the surface and outer margin of a stream of lava 1 Page 95. ri*4it»in <><»jyj^w » — .-K^n^Mimu ^B^S^^ CHARACTEUISTICS OF VOLCANOES 63 4. becomos clogged with fragments resulting from its cool- ing and breaking, it advances slowly, but owing to rupt- ures in the thickened and hardened surface, the still liquid interior escapes from its margin from time to time, being forced out by the pressure from within. The mate- rial thus extruded by reason of its high temperature and fluid condition flows rapidly, spreads out in thin sheets, but cools quickly. Again taking the evidence of an eye- witness : " Scarcely is one of these little offshoots of lava cooled when it is overflowed by another and similar one, and this process is repeated over and over again. In a word, pahoehoe is formed by small offshoots of very hot and highly liquid lava from the main stream, driven out laterally or in advance of it in a succession of small belches. These spread out very thin, cool quickly, and attain a stable form before they are covered by succeeding belches of the same sort." The Scoriaceous Surfaces of Lava Streams. — A charac- teristic of molten lava is that it contains steam and other vapors or gases occluded in its mass. The rock is in a state of aqueous-igneous fusing ; that is, the presence of water allows it to become liquid at temperatures which in the absence of water would not induce a tdiange lo a fluid condition. Occluded steam expands v/hen the lava rises toward the surface and pressure is relieved, and much of it escapes, as is shown by the clouds that form over lava flows. The rapidity with which the occluded steam ex- pands depends not only on the temperature and the rate at which pressure is relieved, but also on the character and condition of the lava. When the lava is highly fluid so as to resemble the liquidity of water, the steam escapes readily ; when it is more viscous, the steam is retained, 04 VOLCANOES OF NORTH AMERICA ]V' U I 1 'I' but expands so as to make the rock op^ i and scoriaceous in structure. Acid lavas, being especially favorable for the retention of the steam, are frequently expanded into a light, frothy substance, termed pumice. Owing to movements in lava after steam cavities are formed in it, the vesicles are frequently drawn out so as to become elliptical or even greatly elongated. The more basic rocks, as basalt, are also affected in the same manner, and become scoriaceous or full of steam cavities, although the process is seldom carried far enough to produce pumice. The formation of steam cavities in still plastic lava may be illustrated by wliat takes place in. bread-making. The carbonic acid generated in dough expands and gives the plastic mass an open, cellular structure ; when the dough is hardened by baking, the cavities remain, sepa- rated one from another by thin partitions. The carbonic acid in the dough plays the role of the steam in still plastic lava, although the expansion of the steam is due to relief of pressure. The lava which has been thus affected, when cooled and hardened, has an open, cellular structure similar to that of bread. A lava filled with an abundance of steam cavities is said to be scoriaceous} Variations in scoriaceous rocks occur, depending largely ^ Igneous rocks contiiiiiing stoaiu hlchs, on cooling and even long after they have lost all of their heat, become permeated with water which perco- lates through them and dissolves some of their mineral constituents. The material thus dissolved is in many instances redeposited in the cavities, which thus become filled with various minerals. Of the minerals thus deposited, quartz is the most common. When the steam cavities tare filled in this manner, and the rock is broken open, hard kernels resembling almonds in shape are found in the openings. Such rocks are called anajf/dnloids. It is to be remembered that in such instances the amygdules are of secondary ori- gin. Agates are formed by this process of infiltration. Cieodes are similar cavities not completely filled. It 1 CHAllACTERISTICS OF VOLCANOKS 05 on the size of the cavities and on the thickness of the walls between them. The cavities are of various diame- ters, from a small fraction of an inch up to an inch or two. When the pressure to which the steam in lava is sub- jected is sufficient, it is prevented from expanding. As the steam escapes, the cavities are closed on account of the pressure about them. It thus happens that lava streams become scoriaceous on their upper surfaces, while within they cool into compact, stony masses, without cavities visible to the eye. A characteristic feature of thick lava flows is, for this reason, the presence of a scoriaceous and porous surface layer, which grades into compact rock below. When the lava is of the proper consistency, steam rises from several inches, and perhaps several feet, below the surface, and tortuous tubes are formed. Again, the passageways for the escaping steam may unite as they approach the surface and lead to the blowing out of more or less material, and the formation of parasitic cones, which have many of the characteristics of true volcanoes. In fact, these parasitic cones are volcanoes in miniature, and differ from primary volcanoes mainly in the fact that the supply of steam and molten rock is small in amount. Parasitic ccjues are sometimes common on lava flows, and may reach a height of even a few hundred feet and have craters at their summits. They are commonly formed of fragments of scoriaceous lava, and emit steam with explo- sive violence, but seldom give origin to streams of molten rock. The upper surfaces of lava streams, then, are character- ized by various features, resulting from the maimer in GO VOLCANOES OF NORTH AMEIIICA : i^.i! ij!)'' Ill i which the hiva cools ; rough aa surfaces occur under cer- tain conditions, smooth but wrinkled and mannnillary surfaces under other conditions ; local concentration of the escaping steam leads to the formation of parasitic cones, and in most cases the surface portions are open and cellular. When a sheet of lava is poured out over the surface of a previous one, the plane of separation is sometimes marked l)y the characteristics just enumerated, but in some instances of this nature the scoriaceous surface of the older sheet seems to have been fused by the heat of the superior layer, so that the two flows arc cemented together and the plane of separation is indelinite. In the walls of the canyons cut through the Columbia lava in Washington, Oregon, etc., ten or more separate flows may be distinguished, which appear almost as evenly stratified as layers of sedimentary rock, in these instances, however, the adjacent layers of basalt are some- times separated by sheets of fragmental volcanic material, produced by violent explosions, and by lacustral sedi- ments, as well as by scoriaceous surfaces. Characteristics of the Bottoms of Lava Flows. — As a lava stream advances, especially during the later stages of its flow, when the surface and margins are in the condition of aa, the blocks cooled at the extremity may be carried under the advancing mass and thus transferred to the bottom of the sheet. Outflow of liquid lava cooling quickly into pahoehoe may become buried in a similar manner. Scoriaceous lava may thus occur on the under side of a lava sheet, as well as on its upper surface. Loose masses of rock lying in the path of an advancing lava stream may become involved in its lower portion, CHAUACTEUISTU'S OF VOLCANOK.S ••I and cracks and openings of various forms, in tlio Hour over wliicli lava flows, nw.y become filled. When lava advances over mud or other loose deposits, they may become involved in the fused rock and perhaps melted or greatly changed. The rocks over which lava spreads .ire usually altered in color and texture as a result of heating, and frecjuently have minerals deposited in them by the heated waters that percolate through them. Changes of this nature are embraced in what is termed contact 'iuctcu/wrphism. The extent of such metamorphism varies, being only a few inches in some instances, and again, when the thickness of the cover of volcanic rock is no greater, reachiijg many feet and perhaps several yards. The principal con- dition controlling the extent to which sedimentary beds are altered on account of the flow of lavas over th<3m, seems to depend on the amount of water they contain. Dry heat induces only local changes; heat accompanied by moisture brings about much deeper alterations. When lava flows over a land surface, the soil is baked and usually reddened by the heat ; if ponds of water ai'e encountered, steam explosions result, and may lead to the formation of parasitic cones on the surface of the flow, and to the formation of sheets of volcanic fragments. Instances a"i^ I2i& 12.2 u liii |L25 II U ,,6 ^ 6" ► V f. /] 7 ? ^. y .<»* V '/ /A Hiotograiiiic Sciences Corporation 33 WIST MAIN STREET WEBSTER, N.Y. 14530 (716) S73-4S03 4' 'V \<. 6^ ^ mmmm na f: 70 VOLCAXOES OF NORTH AMERICA \.l I I f If rl [iff') I' ill I: out may be divided into two groups : the first, including such portions as are plastic when they fall, and the second, such lava fragments as have been torn off of the sides of the craters by the violence of the outrushing steam, and also the liquid lava which is blown into the air, but cools and hardens before reaching the earth. This grouping is arbitrary, as there is no sharp division between plastic and solid volcanic projectiles, but is con- venient for purposes of description and study. An example of the manner in which liquid lava is thrown into the air, is furnished \y the lava fountains that play on the surface of the lake of molten rock in the crater of Kilauea. As described by many observers, columns of lava, almost as liquid as water, are there shot upwards to a height of several hundred, and in some instances of nearly a thousand, feet. The projecting force in these and all other similar instances is mainly, and probably wholly, steam. The molten rock falls before cooliuQi;. The most of it returns to the boilino; lake of lava from which it rose, but some of the drops and clot- like masses reach the floor of the crater beyond the limit of the lake, and on hardening form scoriaceous masses which add to the accumulations of solid material. Driblet Cones. — ^Yllen the fountain-like eruptions of molten rock in Kilauea are less energetic, and especially when they rise through fissures in the crust that floors the crater, the iava divides into drops and falls about the orifices. The drops, being yet hot and plastic, adhere one to another and build chimney-like piles, which Dana has termed driblet cones. These are formed of scoria- ceous, clot-like masses which are sometimes nearly spheri- cal. These semi-fused masses are piled one on another «■ CHARACTERISTICS OF VOLCANOES 71 in such abundr.nce as to form steep conical piles, in some instances a hundred feet or more in height. Occasionally the particles of projected lava are small and descend in showers of loose, smooth-faced, but variously sliaped bul- lets and granules about the vents. ^ The conditions most favorable for the building of drib- let cones occur when the lava is highly fluid, is projected into the air through small openings, and cools sufficiently to become solid but yet plastic before falling. So far as has been reported, these conditions are found only in basaltic craters. The usually thick and pasty consist- ency of acid lavas does not favor the growth of such piles of congealed projectiles as occur in the crater of Kilauea. Pele's Hair. — The air above the seething lake of mol- ten lava on Kilauea is sometimes filled with gossamer threads of glass, which are carried away by the wind and accumulate in large quantities on the adjacent cliffs. This substance is known as Pele's hair, in memory of the Hawaiian goddess of the volcanoes. It furnishes a con- •venient and suitable material, with which birds build their nests. The capillary threads of glass forming Pele's hair resembles the "mineral wool" used as an insulating material for steam pipes, etc., which is obtained by con- ducting a stream of molten slag in front of a strong steam jet; the slag is blown away by the force of the steam, and separates into drops which are drawn out into hair-like threads. When individual threads of Pele's hair are examined 1 J. D. Dana, " Characteristics of Volcanoes," New York, 1890, pp. 158- 160. 72 VOLCANOKS OF NORTH AMEUICA fi<' A' i under the microscope, they are not found to be even and regular. The threads are often tubular, and sometimes branch, or two threads are welded where they cross each other. The glass composing the threads and tubes is far from being pure, but contains rhombic crystals of various minerals as well as air cavities, about which there are expansions of the enclosing glass. The crystals were evi- dently floating in the molten magma before it was spun out.^ The commonly accepted explanation of the formation of Pele's hair, is, that drops o^ fluid lava are thrown into the air during the jetting and splashing of the boiling lava, and drawn out into hair-like threads by the action of the wind. Button states, however, that nothing of this sort was to be observed during his visit to Kilauea, and yet Pele's hair was forming in great abimdance. Wherever the surface of the molten lava was exposed by the breaking up and sinking of the hardened crusts formed on it, the air above was filled with filaments of glass, even when there was no spurting or apparent boiling of the molten material. The explanation of the phenomena offered by Button is as follows : ^ " Liquid L.va coming up from the depths always con- tains more or less water, which is given off slowly and by degrees, in much the same way as champagne gives off carbonic acid when the bottle is uncorked. Water vapor is held in the liquid lava by some affinity similar to chemical affinity, and though it escapes ultimately, yet ^ Descriptions and figures of Pele's hair are given by J. D. Dana, "Char- acteristics of Volcanoes," pp. 100-161, who cites the microscopical studies of C. Fr. \V. Krukenberg. " C. E. Dutton, " Hawaiian Volcanoes," U. S. Geological Survey, 4th Annual Report, 1882-83, p. 108. I 7 I 'I CHAnACTEUISTICS OF VOLCANOES 73 In it is surrendered by the lava with relnctanco so lung as the lava remains fluid. But when the lava solidifies, the water is expelled much more energetically, and the water vapor separates in the form of minute vesicles. Since the congelation of all siliceous compounds is a pa'^sage from a liquid condition through an intermediate stage of viscosity to final solidity, the walls of these vesicles are capable of being drawn out as in the case of glass. The commotion set up by the descending crusts produces eddies and numberless currents in the surface of the lava. These vesicles are drawn out on the surface of the currents with exceeding tenuity, producing myriads of minute filaments, and the air, agitated by the intense heat at the surface of the pool, readily lifts them and wafts them away. It forms almost wholly at the time of the break-up. The air is then full of it. Yet I saw no spouting or sputtering, but only the eddying of the lava like water in the wake of a ship. The country to the leeward of Kilauea shows an abundance of Pele's hair, and it may be gathered by the barrelful. A bunch of it is much like finely shredded asbestos." Volcanic Bombs. — During explosive volcanic eruptions masses of plastic lava are sometimes hurled high in the air, and on account principally of their irregularities of form, acquire a rotary motion, Avhich tends to make them spherical. These revolving masses commonly cool suffi- ciently to harden before reaching the earth, and are more or less perfectly spherical, but at times are still sufficiently plastic when they strike, to be flattened into oval cakes. Projectiles of this nature are termed volcanic bombs. The fact that volcanic bombs rotate during their flight through the air is shown not only by their characteristic V f. "W 74 VOT^ANOKS OF NORTH AMKUICA In II ball-like lorms, bnt also by spiral ridges which sometimes converge towards op})usite poles, thus showing the posi- tion of the axis on vdiich they revolved. Their internal structure sometimes furnishes evidence sustaining the same conclusion. In an example figured by Darwin,^ there is a well-defined shell of com})act lava near the exterior, having a nearly uniform thickness of about the third of an inch ; within is a scoriaceous mass, in which the cells are largest at the centre of the bomb and decrease in size to the inner surface of the enclosino; shell. Darwin's explanation is that the exterior cooled rapidly, and did not allow the steam it contained to expand, while the still plastic central portion cooled slowly. Owing to the centrifugal force due to rotation, pressure was relieved at the centre and allowed the core of slowly cooling lava to become cellular. The distance from a volcano at which bombs may fall must evidently depend not only on their initial velocity, but on the angle at which they start on their flight. During an eruption of Cotopaxi, bombs were thrown a distance of nine miles. Lava balls are described by Dana^ as occurring on Hawaii, that resemble bombs in appearance, but owe their form to a rolling motion in the forward portion of an advancing aa stream, due to friction on the bottom. Certain so-called bombs on Vesuvius are thought to have a similiar origin. Scoria Cones. — Lava not sufficiently fluid to fall in * Charles Darwin, " Geological Observations on Volcanic Islands," 1814, pp. 36, 37. ''J. D. Dana, "Characteristics of Volcanoes," pp. 11, 245. A reference is given by Dana to " The Fragmentary Ejectanienta of Volcanoes," by Johnson-Lewis, in " Am. Jour. Sci.," 1888, Vol. 34, p. 103. ? CHARACTERISTICS OF VOLCANOES Tf) drops l\ 1 i ilfi j ; I I i I i n 1 i §\ expansion is frequently so violent that the rock is disin- tegrated and the fragments projected high in the air. Be- side this primary mode of reducing the lava to fragments, and much of it to the condition of dust, the larger frag- ments as they are shot upwards with a velocity in some in- stances even greater than the initial velocity of shells fired from modern rifle-caimon, strike against one another and against falling fragments, and are shattered, thus tend- ing to increase the quantity of fine, dust-like particles produced. While much fine material originates thus, and is carried away by the wind, many of the fragments that escape comminution fall into the crater from which they were thrown and are again violently ejected, thus multiplying the chances of their being reduced to powder. An eruption of the explosive type thus tends to form much fine dust, which is carried high into the air by the upward rushing c'team and falls most abundantly near the place of discharge. Should a strong wind be blowing, the dust is carried to leeward of the volcano, and on reaching the earth forms a sheet, which, owing to the winnowing action of the wind, is composed of finer and finer fragments, the greater the distance from the volcano. The wide distribution of the dust of Krakatoa, which was probably deposited over the entire earth's surface, has already been referred to. Many instances are on record of volcanic dust falling hundreds of miles from the parent volcano. It is not an unusual occurrence for ves- sels far out at sea to encounter showers of volcanic dust, which whiten their decks. During the winter of 1875-76 dust fell in Norway which was similar to that previously erupted from volcanoes in Iceland, and it was predicted that some volcano on that distant island was in a state •^ ' CHAIIACTEUISTICS OF VOLCANOES 77 'I* of eruption ; intelligence received several weeks later con- firmed the correctnens of this conjecture.' The steam clouds so frequently seen rising from vol- canoes in a state of mild activity when illuminated by the sun are of a brilliant, lleecy white ; should the steam explosions become more violent, the color of the colunm is frerpiently changed to an inky blackness. Tiiis is due to the vast quantities of dust and stones shot u})\var(l with the steam. A grapliic account of the projection of a dark cloud of volcanic dust from Cotopaxi on July 3, 1880, is given by Whymper,'- in recording his observations while on the summit of Chimborazo : " The sky was bright, the air serene ; and long before dawn, sixty miles away, we saw the cone of Cotopaxi clear cut against a cloudless horizon, and remarked how tranquil the great volcano looked, and that not a sign of smoke was rising from the crater. ... At 5.40 a.m. two puffs of steam were emitted, and then there was a pause. At 5.45 a volume of inky blackness began to rise, and went up straight in the air with such prodigious velocity that in less than a minute it had risen 20,000 feet above the rim of the crater. I could see the upper 10,000 feet of the volcano, and estimated the height of the column at double the height of the visible portion of the mountain. The top of the column, therefore, was nearly 40,000 feet above the level of the sea. At that elevation it encountered a powerful wind blowing from the east, and was rapidly borne towards the Pacific, remaining intensely black, seeming to spread very slightly. 1 J. W. .Tudd, " Volcanoes," p. 72. '•^ Edward Whymper, " Travels amongst the Great Andes of the Equator," Xew York, 1892, pp. 320-3;i0. 78 VOLCANOES OF NOUTII AMEUICA i \ n and prcsuiitiii"^ the appoaraiico of a gigantic I, drawn upon an otlua-wiso perfectly clear .sky. It was then caught by wind from the north, and, borne towards us, appeared to spread quickly. . . . For a full hour we saw the innnense colunni still rising from the crater, and then the clouds which were drifting towards us shut it out. " When they connnenced to intervene between the sun and ourselves, the eflectN which were produced were very truly amazing. We saw a green sun, and smears of color something like verdigris-green high up in the sky, which changed to equally extreme blood-red, or to warm brick- red, and then passed in an instant to the color of tar- nished copper, or shining brass. No words can convey the faintest idea of the impressive appearance of these strange colors in the sky, — seen one moment and gone the next, — resembliug nothing to which they can properly be com- pared, and surpassing in vivid intensity the wildest effects of the most gorgeous sunsets. '" About midday the cloud passsd overhead, having taken six hours to travel about eighty miles. The sun then became invisible, and the temperature fell to 15° F. " When the clouds from Cotopaxi first passed overhead, they were still, I think, not less than 5000 feet above us (or 25,000 to 26,000 feet above the sea), and they extended far to the south before the dust of which they were com- posed began to fall upon the summit of Chimborazo. It commenced to settle about ten minutes after our arrival, and in the course of an hour caused tlie snowy summit to look like a ploughed field. It filled our eyes and nos- trils, rendering eating and drinking impossible, and at last reduced us to breathino; throuo;h handkerchiefs." This discharge of dust, as ascertained later by Whym- T* CIIAUACTEIIISTICS OF VOLCANOEH l9 J per, fell over many huiKlrcds of square inilc?*. Its ainoiiiit was estimated at not l(!ss than two millions of tons ; eipial to a column of solid lava (2.G5 speeilic gravity) l\H feet S(|uare and 18,000 feet liigli. Tlic dust which fell on the summit of Chimhorazo was examined microscopically by Professor Bonney, and found to consist of mineral and glass fragments from .02 inch in diameter downwards. Th'i instructive erupticjn from Cotopaxi witnessed by Whymper, although small in comparison witli many dis- charges of dust that have occurred, enables one to (jbtain a graphic idea of what takes place when sheets of line fragments like those which occur in the far west, not only hundreds but thousands of square miles in area and with an average depth of twenty feet or more, are deposited over the land. The sheets of volcanic dust referred to will be described later in connection with other volcanic phenomena in North America. An interesting variation in the manner in which steam escapes from a volcano has been noted in the case of the volcano known as Akutan, on an island of the same name, Alaska. In calm weather immense rings or wreaths of black, dust-charged steam rise from the summit of the mountain and float away one after another and gradu- ally expand as they rise. These wreaths appear to be vortex rini2;s similar to those sometimes blown out of the smoke-stack of a locomotive. Akutan has not been closely examined, but apparently it has a deep fun- nel-shaped crater, and the steam escaping from the liquid lava deep within its throat blows out dust-charged steam in the manner m which vortex rings are found in labora- tory experiments. When the volcanic wreaths are less i I I'lH' i ii 'M m A rt 80 VOI.CANOKS OF NOitTM AMKIUCA well defined, the iisceiuliii^ steam column, convM|)()ndin;^ with the pine tree of Vesuvius, has what iii)[)eiii's to be a spirally twisted trunk. PitOFlLKS OF Vor.CAXIC MOUNTAINS The two varieties oi volcanic eruptions, the quiet and the ex[)losivc, characterized respectively by the emission of streams of highly licpiid lava, and the l)lowing out of fragments, lead to the building of two well-marked types of mountains. When lava is poured out in a highly liquid condition, it flows rapidly, frequently reaching a distance of fifty miles or more, and under favorable topographic condi- tions si)reads out widely so as to form thin sheets. A succession of flows of this nature from the same vent leads to the piling up of layer above layer until a moun- tain with a broad base and gentle slopes is formed. Of such mountains Mauna Loa may l)e taken as the type. Its base at sea level is between fifty and sixty miles in diameter. The mean slope within a circle of five miles aljout the summit crater, as stated by Dana, is about three degrees. At a greater distance from the crater the slope increases to an average of perhaps five degrees. The mountain is thus a flat-topped dome. The reason for the increase in slope at a distance in excess on an average of five miles from the crater, is that the outbursts of lava are usually from the sides instead of the summit of the mountain. Volcanoes in a state of explosive eruption, as we have seen, project scoria, bombs, lapilli, dust, etc., high in the air. Much of this material falls about the orifice from which it was thrown and builds u^ a cinder, or lapilli ■M iff CIIAUACTEUISTICS OF VOJX'ANOES 81 cone : tlic liir^^(fr fnij^nnontM .is a rule fall near the place of eruption, while smaller ones may he carried a great distance. When tlu; ('rn[)tions are long continued, coni- cal mountains are formed hy this process, the sides of which are steep. In many instances, their outer slopes have an inclination of thirty to forty degrees. The angle is determined hy the "angle of repo.se" of the material of which the C(mes are huilt, and varies with tin; size and angularity ot the fragments. Mountains of this type are illustrated especially by Fusiyama, Japan (Plate 3); PROFILE OF SHISHALDIN; DRAWN FROM A PHOTOGRAPH; SCALE ABOUT 10,000 FT.= \ INCH. PROFILE OF LOA AND KILAUEA; AFTER J. D. DANA; SCALE ABOUT 10 MILES= 1 INCH. Via. 2. Profiles of volcanic mounUins. Tlio upper diaftr'^m shows the characteris- tic ontliiio of a cone resultiiiK from mild explosions ; tUo lower diagram, the form produced by the qiiiet offusiou of highly litiuid hivii. Shislialdin, on Unimak Island ; and St. Augu.stine, Cook's Inlet (Plate 3), Alaska. Nearly all of the coni- cal volcanic piles on the earth are of this class, but in most instances the regularity of their slopes has been modified by overflows, or outbreaks of lava, and by erosion. Not only are the sides of volcanic cones built of frag- mental material, steep, as already mentioned, but when seen in profile they present regular and very beautiful curves, as may be seen from the accompanying illustration of Fusiyama. The reason for this characteristic curva- fj i' 82 VOLCANOES OF NOUTH AMLRICA n '■ i J' lure, as determined by Becker,' is that it is the figure of greatest stability. Between dome-shaped volcanic mountains with fiat tops, and conical piles with a sharp apex and concave surfaces, there are many intermediate forms. These variations depend principally on the alternate extrusions of projectiles and of lava from the same vent, which leads to the building of compound cones, the most usual type; the location of the opening through which lava escapes, whether from the summit or through the side of a crater ; the degree of fluidity of the lava, whether highly liquid or thick and viscous ; and the size and shape of the frag- ments thrown out during expletive eruptions. The extrusion of highly liquid lavas, as we have seen, leads to the building of mountains with very gentle slopes, as in. the case of Mauna Loa ; highly viscid lavas, on the other hand, sometimes congeal in nearly perpen- dicular cliffs, as in the case of some of the Mono craters, California, described later, but in such instances lofty mountains are not formed, owing apparently to the clog- ging of the conduits through which the lava is emitted. Instances are cited by Judd,^ in which lava so viscous that it refused to flow on reaching the surface, has been forced out from volcanic vents and congealed in. obtuse, steep-sided columns, having a concentric internal structure. The form and structure of these peculiar elevations has been imitated by forcing a thick paste of plaster of paris, vertically upward through a hole in a 1 G. F. Becker, " The Geometrical Form of Volcanic Cones and the Elastic Limit of Lava," in " American Journal of Science," 3d series, Vol. 30, 1885, pp. 283-293. 2 J. W. Judd, "Volcanoes," pp. 125, 127. VOI.CAXOKS OF NOHTH AMKKICA. I'l.ATK n. Fio. A. Fusiyuina, Japan. A typical lapilli cone. Fig. B. St. Aii{;ustine, Cook's Inlet, Alaska, 18',I5. (Photograph by U.S. Geological Survey.) lir !|f V^-: >l n «||J«W1 I CHAUACTEUISTICS OF VOLCANOES 83 board. In the experiment, the layers first formed were raised and expanded by the paste which followed, so as to form an oval or bell-shaped mass, which, when cut through, exhibited an onion-like structure. Examples of hills of this nature are said to be furnished by many andesitic volcanoes in Hungary, certain phonolite hills of Bohemia, and more definitely by the so-called " manie- lona" of the Island of Bourbon. Illustrations of the latter are given in the book just cited. The most regular and by far the most Ijeautiful cones, formed of projectiles, are such as are built up by the blowing out of fine dust and gravel-like fragments. The angle of repose of such material is less than that of rough scoria, and hence the sides of the cones formed of it are less steep than the slopes of cinder cones. When cinders are plastic at the time of their fall, they fuse together or adhere one to another, as in the case of the driblet cones of Hawaii, and form the steepest of all the various structures built about volcanic vents. Structure of Volcanic Mountains What arrangement of the material composing volcanic mountains would be revealed, if we could cut them from summit to base through a vertical plane and remove one half of the mass ? The surface thus exposed would be a vertical section. Although it is not possil)le to obtain complete sections of this nature of such vast accumula- tions, yet volcmoes are sometimes breached by explosions from within, and variously dissected by erosive agencies acting from without. By studying the anatomy of vol- canic mountains where thus exposed, we can learn many facts concerning their mode of growth 84 VOLCANOES Ol<' NOUTII AMERICA m Mruntains formed of Lava Sheets. — Mountains made entirely of lava flows when dissected l)y erosion, reveal the edges of the iml)ricated layers of which they are com- posed. Those, in normal instances, dip away from the crater and are of very irregular thickness. A sheet may have its maximum thickness near the vertical axis of the mountain or at a distance from it, depending on topographic conditions, the viscosity of the lava, and other causes. The overflows in the earlier stages of a volcano's growth are connnonly from the crater, hut as the mountain be- comes higher, the force required to raise the liquid rock to the summit is increased, and relief is frequently found through fractures in the crater walls, aided perhaps by the melting of the rock of which the mountain is composed. In undisturbed sedimentary beds the higher layers in a series are younger than those below. This is not an invariable rule, however, in the case of the imbricated sheets forming many volcanic mountains, since an erup- tion of lava may escape from beneath the margin of an older and previously hardened layer. What have been termed " imbricated mountains " by Powell, in which the surface layers have much the same arrangement as the tiles on a roof, the lower layers being the younger, have the structure here referred to. The sheets of lava poured out in various ways so as to build up mountain masses, are not continuous all about the crater from which they were extruded, but in most instances are comparatively narrow streams radiating more or less definitely from the centre, which overlap at their margins and may even cross one another. In exceptional instances, as already stated, lava is extruded in an extremely viscous condition, as is the case ■■i CllAKACTEUlSTICS OF VOLCANOES 85 of the '• inamelons " of the IsUind of Bourbon, and rises into obtuse columns and dome-like forms, which have a concentric, onion-like structure, when seen in section. Cones formed of Projectiles. — The structure of a vol- canic pile composed wholly of material projected into the air during explosive eruptions, is strikingly different from that of mountains built wholly of lava sheets. As we have seen, the topographic form produced by scoria, lapilli, and dust falling about a volcanic vent, is that of a cone. ■\''-=itiI-V .:•^l^^bVfe^■■^•riii,:•^l•■•'-•J:•.^• * . Fig. 3. — Experimental illustration of the mode of formation of volcanic cones com- posed of fra';mental material. (After J. W. Jiuld.) The arrangement of the layers in a vertical section of such an accumulation may be illustrated by a simple experiment. If a tube is inserted from below, in a hole in the centre of a table, and sand, sawdust, and other similar material is blown through the tube by means of a bellows, it will rise from the opening and fall about it so as to form a conical pile, with a depression in its summit. If black and white material is alternately blown through the tube, a vertical section of the cone that is formed will have the structure illustrated in the above diagram. 86 VOLCANOES OF NOllTH AMERICA \. I I 1 The size of the cone obtained by such an experiment, the steei)ne8s of its sides, etc., will vary with the amount and character of the material used, and the strength of the air current ; but the arrangement of the layers or their structure, exposed in a vertical section, will remain essen- tially the same. The layers are continuous all about the orifice, Ijut are inclined in two directions from the rim of the central depression or crater. The pile has the appear- ance of being formed of two sets of cones, the smaller set being reversed and fitting into a hollow in the truncated summit of larger series. The inclination or dip of the inner layers is greater than that of the outer layers. The arrangement illustrated above has been found to be characteristic of the structure of many volcanic moun- tains. In place of the mechanical regularity shown in the experiment, however, actual lapilli cones commonly exhibit marked irregularities, due to the blowing away of l)ortions of their walls, and the subsequent filling of such breaches, and to variations in the intensity of the erup- tion which may admit of the building of a small cone with double slopes, within the crater of a larger structure. Some of the irregularities found in nature are shown in the following ideal action of Vesuvius. Variations and irregularities also occur on account of the effect of the wind, and the inclination at which the projectiles start on their aerial journey. A lapilli cone in the region of the trade winds, for example, is usually found to be higher and more massive on the leeward than on the windw^ard side. But in spite of all these modifying conditions, the lapilli cones in various stages of dilapidation that have been studied, exhibit in greater or less perfection the characteristic internal structure ob- I i. I i "t. CHARACTERISTICS OP VOLCANOES 87 tained when analogous artificial cones are formed, as in the experiment cited. Composite Cones. — Although mountains composed en- tirely of lava sheets, or made wholly of projectiles, may exist, the structures described as characteristic of such mountains are rather theoretical than illustrative of what one liiids when the study of actual examples is under- taken. In the history of most volcanoes there have been times when lava has flowed down their sides, and again. ' .» 5 Modem, i JUetrU J-ofO' i Sccria Bolt. 7 InAUuig of Ortat QyOtr of A.D. 19 6 -Pre Ajj&rjc 6edt cf Sarria S Lanu 5£arly Vauinnn be "When, ai Us maacdjnz^m- MJUd^ of Monte Somma^ IXTedanveniaux^ nj)yhu. fl.OraUr W Vent of ordinary MruplioTU 0. Vent ofJiu-ocqysmai£ruplions. Fig. 4. Diagrammatic general section through Vesuvius at the present time, showing the structure, the substructure, aud the successive accumulations. (After J. L. Lobley.) periods when explosions have occurred and fragmental material spread over the previously formed lava sheets. Commonly, many such alternations in the character of the eruptions have occurred, and the mountains that result have a composite structure — sheets of lava alter- nating in an irregular way with layers of scoria, bombs, lapilli, and dust. The slopes and contours of composite volcanic moun- tains are as varied as is their internal structure. When 88 VOLCANiJliS OF NOUTH AMEIIICA V\ ^(l lava flows predominate over the fragmental deposits, their shapes approacli tliat of the typical flat-topped domes, of which Mauna Loa is an example; when the projectile material is in excess of the lava poured out in a fluid condition, cones with small apical angles and steep, concave sides, approximating to the form of Fusiyama, are produced. These contrasts are illustrated in Fig. 2. It is the fate of mountains, inclusive of those of vol- canic origin wliich escape destruction by explosions, to be slowly removed by erosion. During this process the secrets of their interior are revealed, and the nature of their internal structures controls the character of the topographic changes they pass throngh. Dikes. — The structure of volcanic mountains, of what- ever type, is subject to important modifications due to the opening of fissures and the injection into them of molten rock. Tlie lava filling such fissures and hardening, forms sheets wliich may be vertical or horizontal or occupy any intermediate position, and in fact frequently change from one position to another that is quite different, in the same example. Such sheets of intruded lava which cut across the bedding of the rocks they invade are termed dikes. The fractures formed in volcanic mountains frequently radiate from their centres, and occasionally cleave their sides from base to summit. Such fissures when filled with hardened rock add greatly to the strength of the piles they traverse, and furnish some of the most strongly pronounced topographic features when volcanoes are dissected by erosion. The sheets of lava, scoria, and lapilli in composite vol- canic mountains are frequently bound together by sys- tems of dikes, which perhaps intersect one another. The I i ' '" ' '"■U W jm p »j i CHAnACTEHISTICS OF VOLCANOES 89 departures that volcanic mountains coiunionly present from the .simi)le, ideal type of lava dt^mes or la})illi cones depend therefore not only on the manner in Avhich they arc formed, hut on suhsecpient internal changes. Still further complications arise when the molten rock, forced into fissures, reaches the surface and outflows, forming surface sheets, and when explosions, or hasal melting, remc e portions of a mountain. Volcanic Necks. — The passageways or conduits leading to volcanoes from deep below the .surface, and furnishing a passageway for the material erupted, are left filled with molten lava when the surface activity cea.ses ; this material slowly cools and hardens into compact rock, and forms what are termed volcanic necks. The conduits of active volcanoes may be completely filled with molten lava, as is the case when craters over- flow. If the energy declines while a volcano is in this condition, its crater will have a lloor of lava, which is the summit of a column or plug, the lower portion of which, perhaps miles beneath the surface, may be still in a highly heated and plastic condition. At other times, the liquid lava within a crater and in the upper portion of the con- duit that leads to it, may be drawn off through fissures in the sides of the volcano, thus causing the surface of the lava column to fall to the level of the opening, leaving a more or less conical depression, perhaps two or three thou- sand or more feet deep. If the activity declines while the volcano is in this condition, the crater will remain as an empty bowl which, especially in humid climates, may be- come filled with water and transformed into a lake. However diverse the conditions that attend the growth of a volcanic mountain, a core of lava occupies its centre 90 VOLCANOKS ♦' tlic jtrcs.siirt' wliicli c;iii.s(!.s tlio inaj^iMiiM tints I'oriiicd to rise in (issuros and lead to the I'orniation ol' various chisses of intrusions and to vol(;anoes. are distinct and should he separately considered. What may he considered as a continuation of the lines of thought here suggested, will he found in next t(j the hist cha[»ter of this hook. ClIAItACTKIJISTIf'S OI-' IciNKUUS RoCKS The rocks of which the earth's crust is conii)osed present great diversity. In order to avoid confusion from the endless variatiims they exhihit, it is convenient to classify them iirst of all in three great gr(ju[)s : namely, ujncous, .sediincntari/, and mdainorphlc, rocks. This may he con- sidered the general order in which the rocks were formed since the iir.st crust of the earth, under the most plausihle hypothesis that has heen presented, was produced hy the cooling of fused material. Where this primal crust rosa. ahove the sea, it was disintegrated and worn away so as to furnish material for sedimentary heds. At a later date, both volcanic and sedimentary rocks were in many locali- riis intensely heated and underwent great mechanical, chemical, and mineralogical changes, which led to marked alterations in all of their characteristics. These altered rocks are said to be metamorphosed. They constitnte the third great group mentioned above. In the restiicted view of nature presented in these pages, we have but little to do with sedimentary and metamor- pliic rocks, and will therefore find it most advantageous to concentrate our attention on some of the leading char- ■ nf..."!!;: CMAIIACTKUISTICM OF VULCAXOKM KIT 'I'ks ires lloiis L\y iiics It lit' iicturistics (jf the rocks which wen; once in u .state of fusion anit.JLWkH£bi A-NM<^.tu.«u^i<.fi^u ^ J! f^jr>is;!^imj.A^iJiii ' ' •".T"""" - ' -.'- "•tr-r-.r. mamnsm 118 VOLCANOES OP NORTH AMEItlCA I i A i ill r \ M lihl ;-< ;ii ' 1 1 9 1 !i lization predominates. Two leading classes of rocks are thus recognized : 1st, the holo-crystaU'uic or granitoid rocks, the type being granite, composed of crystals belong- ing to a 8inj^le_ epoch of crystallizatign, but in which neither an amorphous ground mass, nor crystallites (small, undeveloped crystals) are present ; 2d, the semi-crystal- line or trashjtoid rocks (the type being trachyte), dis- tinguished Ijy a more marked contrast between the crystals of the first and second periods of consolidation, and the presence usually of an amorphous ground mass in which the crystals are embedded. To these a third and subordinate class is sometimes added lo include such rocks as are composed wholly of glass, without emljedded crystals. Under each of these family groups several genera, as they may be termed, and numerous species have been recognized. A few of the most common genera are noticed below. The first, granite, will serve as a repre- sentative of the great class of wholly crystalline rocks to which it has given a name ; while the others, basalt, rhyolite, trachyte, and andesite, will stand for the equally great, and yet more diversified, class of semi-crystalline rocks. Granite. — The great diversity in color and texture of the rocks of this type is probably familiar to the reader from the many varieties used for monumental and archi- tectural purposes. Its color varies through many grada- tions from dark gray or nearly black, to pink and red, according to the predominant mineral constituent. The minerals composing granite are quartz, feldspar, and mica, but many times accessory minerals occur in abundance. The quartz is readily recognized from its resemblance to l\ *■■ I' J CHARACTEUISTICS OF V(JLCANOES 119 clear glass, its liardness (it will scratch glass), and the fact that it is without cleavage; that is, it will hreak in one direction as readily as in any other, the surfaces of fracture being uneven. The feldspar varies from white to pink in color, and cleaves easily along certain parallel planes, pro- ducing smooth brilliant surfaces. It is softer than ([uartz, can be scratched with a knife, but will not scratch glass. The mica splits easily into thin plates or scales, which arc ela.stic. It is softer than the feldspar, and frequently dark in color and even black. If one examines a piece of polished granite either with a pocket lens or a microscope, it will be found that with the possible exception of certain accessory minerals, it is composed of more or less perfect crystals of the three minerals described above, which interlock with one another in almost all instances without an intervening glassy or micro-crystalline ground mass ; that is, all of the substance present has been crystallized — the rock is liolo- crystalline. Recent studies have shown, however, that while nothing like a vitreous ground mass can be dis- covered, certain granites do contain a minutely crystalline ground mass, in which the larger crystals are embedded. This illustrates the fact that even the larger groups into which rocks are divided are really artificial ; in reality, there is no sharp division between holo- and semi- crystalline rocks. Their crystalline condition depends largely on the rate at which they cool. Between those which cool so slowly that all the material present passes to a crystalline condition, and those which cool more rapidly, but yet harden before all of the material present has assumed definite crystalline forms, there must of necessity be a complete gradation. ja ^titoirffi^^aa* * *^^^ :^V,^..-^.^^..-;.t..-^-.^^ .■^..■wt>-,»>it.,^,. ., - 120 VOLCANOES or NORTH AMKKICA I' •' i t Ik It I I I rn r ■ While granito docs not occur in the contUtion of a surface (low and is not known to have been produced by volcanouH, it i.s found abundantly as bosses and dikes and forming vast masses which were intruded in a molten or plastic condition among other rocks, and now exposed by deep erosion. It also occurs as the surface rock over vast areas, where, again, great erosion has taken place. In such instances it is sometimes found to pass on its border into gneiss and schist and other rocks that are termed nietamorphic ; that is, it passes by insensible gradations into rocks usually of sedimentary origin, that have been changed by pressure, heat, and the passage through them of heated waters, into a crystalline condi- tion. These nietamorphic beds, again, when examined at a distance from the granite, aro sometimes found to pass by insensible gradations into hiary sedimentary strata like shale, limestone, etc. In such instances it is plain that the gneiss and schist have been formed by the altera- tion of sedimentary beds, and the inference is that the granite is but another step in the same process. Granite also occurs in the axes of many mountain ranges, where elevation and deep erosion have taken place. Occasionally the side of a fracture in the earth's crust has been upraised, perhaps many thousands of feet, so as to expose granite as the basal member of a great series of rocks. It appears, therefore, that granite may be either an igneous or a metamorphic rock. Igneous, when it has been in a state of fusion and allowed to slowly crystallize ; and metamorphic when the original material changed to a crystalline form without complete fusion. Between the two processes there is a complete gradation, and no one can say where the boundary line should be CIIAUACTEKI8TICS OK VULCAN(JES 121 drawn. To wliu^li class a samplo of granite belongs can only be dctcnnincd by litdd study, and even then a definite answer cannot always be obtained. Granite as a rule deconiijoses wben exposed to tlie act'on of tlie atniospbcre, witb coniiiarative ease. Tlie feldspar yields to solution. The ([uartz is broken by changes of temperature, etc. ; the mica separates into flakes and scales. These surface (;hanges f recjuently extend to a depth of one or two hundred feet. When the de- cayed rock is within the reach of streams, it is washed away and its various ingredients assorted, and in many cases deposited separately. The decomposed feldspar forms clay, some of which is pure white and known as kaolin or china clay ; the quartz forms sand, in which si)angles of mica commonly occur. Basalt. — Next after granite and allied rocks, the most abundant crystalline rock that the student of the earth's history is apt to meet, is basalt and its near relatives. Familiar examples of the occurrence of basaltic rocks are furnished by the Palisades of the Hudson ; Blomidon and North Mountain, Nova Scotia ; Mts. Holyoke and Tom, Massachusetts ; the Columbia lava of Oregon, Washington, and adjacent states ; the products of the Hawaiian volca- noes ; the columnar rocks of the Isle of Staffa, Scotland, and the Giant's Causeway, Ireland, and at many other localities. Ba.salt is normally a dark, heavy rock, varying in com- pactness from scoria filled with steam cavities, to a dense material without visible apertures. It varies, also, in texture from coarsely crystalline, when distinct crystals are visible to the naked eye, to cryptocrystalline, and in some instances is a compact black glass with perhaps 122 VOLCANOES OF NORTH AMERICA i^ ill i [I I i^(.'! f V'l ill (?'■ minutej immature crystals. The minerals composing it are essentially feldspar, augite, and magnetite. The feld- spar is most abundant, and is usually the species known as lahradorite, which, like nearlv all of the group to which it belongs, is essentially a silicate of alumina, but is com- paratively poor in silica. Other and more highly silicated feldspars, however, may take the place of the labradorite or be associated with it. The light-colored crystals to be seen in coarse-grained basalts are feldspar ; sometimes two varieties may be distinguished by the unaided eye. The augite and magnetite are dark minerals, the magnetite being always black, and give to the rock much of its sombre tone. With these more essential minerals, others, such as olivine, leucite, mica, garnets, etc., may be de- veloped as accessories. Labradorite is the most easily fusible of the feldspars; augite and magnetite are also easily fusible, so that basalt melus at a comparatively low temperature. Between 2000 and 2400 degrees of the Fahrenheit scale under ordinary atmospheric pressure it becomes fluid. Basalt forms by far the larger part of the lava poured out by modern volcanoes, and occurs also in many dikes and in both extruded and intruded sheets. It is the most common of all the recks with which the student of vol- canoes has to deal. Rhyolite (known also as liparite and quartz-trachyte) is composed of a fine-grained ground mass with crystals or crystalline kernels of sanidine (a glass-like feldspar), quartz, black mica, and hornblende, and a considerable vari3ty of less abundant minerals scattered through it. While considerable diversity is exhibited in its texture, it may usually be recognized, or at least have its identity CHARACTERISTICS OF VOLCANOES 123 suggested, by a certain flow-like arrangement of the min- erals of which it is largely composed. In most instances it is apparent that the magma was fluid after the larger crystals had been developed in it and that a flowing motion caused the crystals to be arranged with their longer axes in parallel directions. This flow structure and the presence of prominent crystals of sanidine and quartz are the characteristic features that catch the eye in rough field examinations. Rhyolite varies in color from black and dull gray to light pink and even pure white, and also exhibits all degrees of texture from light, porous pumice to compact glass. It is a common product of volcanic eruptions, although occurring in connection with but few still active volcanoes. It was poured out abundantly in compara- tively recent geological times in the western part of the United States, and forms large portions of the mountains of Utah and Nevada. Its brilliant colors frequently give to the mountains of that arid and but scantily plant- clothed region, as rich and varied tints as are seen on the hills of New England in autumn. Rocks composed of angular fragments of rhyolite, cemented so as to form a light, porous mass, termed rhyolitic tuff, occupies large areas in the Cordilleran region, and frequently surpasses the outcrops of massive rhyolite in brilliancy and variety of color. The Sunset Hills, Nevada, have been so named in reference to the varied color imparted to them by the tuff of which they are largely composed. Some of these tuff deposits are direct accumulations of lapilli, blown out of volcanoes in a state of violent eruption; while other deposits, frequently of great extent, are of the nature of mud • ■-^.^..^^-.•.■.. 124 VOLCANOES OF NORTH AMERICA %i 1. 1 flows, the ejected fragments having been mixed with water so as to render the mass plastic, and allow it to flow even on gentle slopes. The rhyolites are acid rocks, and among the most difficultly fusible of any of the volcanic series. Analyses of fifteen samples from widely separated localities, com- piled by J. F. Kemp, show from 63.63 to 83.59 per cent of silica. Trach3rte. — This name was originally applied to a large group of rocks, characterized principally by their roughness and harshness to the touch, to which the name refers, but is now restricted to certain compact, porphy- ritic material, containing, as essential ingredients, sanidine with some other feldspar, and usually hornblende, biotite (black mica), magnetite, and other less common minerals, scattered through a glassy or finely crystalline ground mass. Trachyte is distinguishable from rhyolite by the ab- sence of quartz in conspicuous grains or crystals, and also by the absence of a flow structure. It is normally dark colored, but seldom has the black or greenish-bladk color of basalt, and differs from that rock also in containing sanidine, and being without grains or crystals of olivine. The trachytes are less acid than the rhyolites, the silica varying, ordinarily, from 57 to 66 per cent. Andssite. — The rocks of this widely distributed group were first studied in the Andes, whence the name, and are described by E. H. Williams, as generally dark, and mostly fine-grained rocks, with a restricted amount of glassy base, but larger than in the trachytes. When examined under the microscope, they reveal a felt-like mass of minute crystals of plagioclase, hornblende biotite, w CHARACTERISTICS OF VOLCANOES 125 V and pyroxene, and may or may not contain quartz. In hornblende-andesite, crystals of plagioclase, hornblende in large black prisms and needles, and some augite may be distinguished by the unaided eye. In mica-andesite, biotite predominates over the hornblende. The variety characterized b}^ the presence of large-sized crystals of hornblende is common in the Cordilleras from Central America to Alaska, and in the prevalent rock met with in many of the great volcanic mountains of which Mt. Rainier and Mt. Shasta are representative. The andesites contain from 56 to 67 per cent of silica, corresponding in this respect very closely with the trachytes. Summary. — Under each of the typical and character- istic igneous rocks mentioned above, there are many subdivisions, and besides, there is a host of rock species, some of them common in many districts, that cannot be classed in the group to which attention has been directed. To attempt a more extended introduction to the study of rocks, however, is impracticable at this time ; one reason being that the subject is so attractive that the reader would be in danger of losing sight of the main object of this book. Petrology is a highly specialized branch of geology, and one concerning which the general student cannot hope to obtain more than an unsatisfactory in- sight. Unfortunately, there is no ready way in which the species of fine-grained igneous rock can be certainly distinguished one from another, without the use of some- what expensive apparatus. Thin sections have to be ground and examined with a microscope adapted to the purpose, before their mineralogical composition can be determined, and oven then, owing to the great number mM ^!*m tmM mt t i f i^ w -* .^-;: 126 VOLCANOES OF NORTH AMERICA of varieties that occur and their gradations one into an- other, and the alterations that have taken place in numer- ous instances since the original cooling of the magma, no entirely satisfactory scheme of classification seems possible. The best that the beginner can do is to become acquainted with a few types of the most common occur- rence. A few books have been mentioned in a preceding foot-note for the benefit of the student who may wish to learn more of the science of petrology. y, I CHAPTER II GENERAL DISTRIBUTION OF THE ACTIVE AND RECENTLY EXTINCT VOLCANOES OF NORTH AMERICA On the accompanying map, Plate 1, the distribution of the active and recently extinct volcanoes of the world is shown with as much accuracy as the scale of the map will allow. The most prominent fact brought out by a study of the geographical distribution of volcanoes is, that, with but few exceptions, they are situated on the borders of continents or on the ocean's floor, and are notably absent from the central portions of continental areas. An inspection of the map just referred to, will show that the volcanoes of North America form a part of a great system of volcanic vents which may be said to sur- round the Pacific Ocean. This chain of fire, as it has been termed, beginning in Terra del Fuego, extends along the west border of South America, where its course is marked in the Andes by some of the loftiest igneous mountains in the world ; it is narrow and well defined on the west border of Central America and far into Mexico, where still steaming craters, some of which are among the highest summits on the continent of North America, define its position. The volcanic belt broadens in the northern part of Mexico and the United States, but is unmarked by active craters. Again contracting and approaching close to the ocean's shore, and in several 127 "■tmwrw mmm DM '•'{ ml i 'h I' 128 VOLCANOES OF NORTH AMERICA instances marked by island volcanoes, the igneous belt follows the coast of British Columbia and Alaska, and extends westward throughout the length of the Aleutian islands. Still active craters in Alaska show the positions of earth fractures which unite the volcanic belt of the New World with the still more energetic volcanoes of Kamchatka, Corea, Japan, Formosa, the Philippine islands. New Guinea, New Hebrides, New Caledonia, and New Zealand. The length of this vast system of active vol- canoes, from the southern end of South America about the northern Pacific to New Zealand, is about 30,000 miles. Within the embrace of the great curve, and rising from the deeply submerged floor of the Pacific, are many volcanic islands and still active craters. A branch of the western arm of the volcanic system just referred to, embraces Java, Sumatra, etc. A corre- sponding offshoot of the eastern arm is marked by the volcanoes of the West Indies. It is a matter of observation that the loftiest mountains of a continent face the largest ocean washing its shores. In a similar wa.y it may be remembered from a study of the distribution of volcanoes, that the greatest volcanic belt in the world embraces the largest ocean. Whether this association indicates an essential or genetic connec- tion between the height of mountains or the prevalence of volcanoes, and the extent of water bodies, remains to be shown. The volcanic areas considered in this book form a part of the great Pacific belt, but include an exceptional por- tion of it, since from Central Mexico to southeastern Alaska there are no active vents. In this interval of some four thousand miles, however, there are many -'::T -*-rr'--.rr'j*iFjsa=-- i . ji^i Ed tf Q DISTUIIJUTIOX OF VOLCANOES 129 recently extinct craters, as well as hot springs and gey- sers. It is in this break in the chain of steaming craters that the breadth of the volcanic belt is greatest. This coincidence is significant, as will be .shown in advance. An examination of the accompanying ma}) of North America, Plate 4, in which the positions of most of the active and recently extinct volcanoes are indicated, will show that our studies are to be confined to the Avestern portion of the continent, and for the most part, to the im- mediate border of the Pacific. No volcanoes sufficiently recent to be recognized by their topographic forms occur east of the sharply defined eastern border of the Cordil- leran mountain series. The central and eastern portions of the United States, the central, eastern, and northern portions of Canada, and mnch of Alaska, excepting its immediate southern border, are without evidence of recent volcanic activity. No active or recentl}' extinct volcanoes have been discovered in the Greenland region. Iceland, as is well known, is an active volcanic centre, but, as stated in the introduction, is not included in our present studies. The most recent volcanic rocks in all of the vast region just referred to — east and north of the Cordilleran series and embracing five-sixths of North America — are, so far as known, confined to the Atlantic border and occur in the Newark system. Some accounts of these rocks have already been given in connection with other igneous intru- sions. They were poured out in part as molten lavas during the Mesozoic era, or the middle *age of the earth's geological history. Erosion has been so great since the volcanoes from which they came were in activity that scarcely a vestige of the cinder cones or of the mountains ^^^^^Krmm 130 VOLCANOES OF NORTH AMEUTCA ii *SFi.«V'i" KiJt»¥4» wCaai^^>* *. V VOLCANOES OF CENTRAL AMERICA 147 Fifteen days after tlie visit of DoUfus and xMont-Serrat, Izalco was again in a state of violent eruption. Birth of a Volcano in Lake Ilopango, Salvador. — Lake llopango, in tlie central part of Salvador, was the centre of a violent earthquake in 1879, which was followed by a rapid discharge of the water of the lake. In the course of fifty-four days the lake fell thirty-five feet, and dis- charged a volume of water through a surface channel, estimated at over 20,320 million cubic feet. During the earthquake the lake was greatly agitated, and immense volumes of steam rose from its central portion. On Janu- ary 20, 1880, at eleven o'clock in the evening, a renewal of the disturbance of the water was noticed, and the next morning a pile of rocks was seen in the centre of the lake, from wliich rose a huge column of vapor. The eruption continued for more than a month ; the island of rocks in- creased in size, and from it rose continuously a vapor column fully a thousand feet high. The waters of the lake became heated, and sulphurous vapors were emitted in such abundance as to be unpleasant when the wind blew from the east, in the city of San Salvador, about ten miles distant. Pre" ious to the disturbances just mentioned, Lake Ilo- pango was abundantly stocked with fishes, which were killed at an earlv sta'/e of the outbreak. When the erup- tion terminated, the island tliat had been formed was found to have an area of about five acres, and a height of 160 feet. In its immediate vicinity soundings showed a depth of 100 ffithoms of water. Tho region all about Lake Ilopango is composed (jf volcanic rocks, and judging from the accounts available, the most authentic of wliich is a report by Edwin Rock- 148 VOLCANOES OF NOUTII AMERICA I M' i stock to the government of Guatemala (San Salvador, 1880), it seems as if the lake occupies an ancient crater or perhaps a depression due to subterranean explosions, the outlet of which had been dammed by landslides. The partial drainage of the lake, as well as the formation of a volcanic island in its centre, are among the changes of greatest geographical interest that accompanied the eruption. A Nameless Volcano in Nicaragua. — In the account of the volcanoes of Central America given by Squier, already referred to, there is an interesting description of the breaking forth of a new crater in the beautiful Plain of Leon to the southwest of Lake Nicaragua. This unique phenomenon is described as follows : '" In fact, 1 have been a personal witness of the origin of a new volcano, which, if it does not meet a premature extinguishment, bids fair to add another high cone to those Wiiich now stud the great Plain of Leon. . . . On the 11th and 12th days of April last [1850], rumbling sounds, resembling thunder, were heard in the city of Leon, situated in the centre of the plain I have described. They seemed to proceed from the direction of the vol- canoes, and were supposed to come from the great volcano of Momotombo, which often emits noises and shows other symptoms of activity, besides sending out smoke. This volcano, however, on this occasion, exhibited no unusual indications. The sounds increased in loudness and fre- quency on the night of the 12th, and occasional tremors of the earth were felt on Leon. Early on the morning of Sunday, the 13tli, an orifice opened near the base of the long-extinguished volcano of Las Pilas. about twenty miles distant from Leon. The throes of the earth at the I 'iii VOLCANOES OF CENTKAL AMERICA 149 time of the outburst were very severe in the vicinity, resembling, from the accounts of the natives, a series of concussions. The precise point where the opening was made might be said to be in the phiin ; it was, however, somewhat elevated by the lava which had ages before flowed down from the volcano, and it was through this bed of lava that the eruption took place. No people reside within some miles of the spot ; consequently I am not well informed concerning the earlier phenomena ex- hibited by the new volcano. It seems, however, that the outburst was attended with much liame, and that, at first, quantities of melted matter were ejected irregularly in every direction. Indeed, this was clearly the case, as was shown upon my visit to the spot some days there- after. For a wide distance around were scattered large flakes resembling freshly cast iron. This irregular dis- charge continued only a few hours, and was followed by a current of lava, which flowed down the slope of the land toward the west, in the form of a high ridge, rising above the tops of the trees, and bearing down everything which onposed its progress. While this flow continued, which it did for the remainder of the day, the earth was quiet, excepting only a very slight tremor, which was not felt beyond a few miles. Upon the 14th, however, the lava stopped flowing, and an entirely new mode of action fol- lowed. A series of eruptions commenced, each lasting about three minutes, succeeded by a pause of equal dura- tion. Each eruption was accompanied by concussions of the earth, too slight, however, to be felt at Leon, attended also by an outburst of flame a hundred feet or more in height. Showers of red-hot stones were also ejected with each eruption to the height of several hundred feet. > it i4 ', I. I' M .."-.. . -r il 'B. •r * > " npi 150 VOLCANOES OF NORTH AMERICA r ; Most of these fell , 'wk in the mouth or cmter, the rest falling outward, and gradually building up a cone around it. By the attrition of this process, the stones became more or less rounded, thus explaining a peculiarity in tlie volcanic stones already alluded to. These explosions con- tinued uninterruptedly for seven days, and could be accu- rately observed from Leon in the night." Observations made by Squier and his companion. Dr. J. W. Livingston, on visiting this young volcano, show that it presented on a small scale many of the phenomena to be seen when Vesuvius and other similar volcanoes are in eruption. " In order to obtain a full view of the new volcano, we ascended a high, naked ridge of scoria, entirely overlook- ing it. From this point it presented the appearance of an immense kettle, upturned, with a hole knocked in the bottom, forming the crater. From this, upon one side, ran off the lava stream, yet fervent with heat, and send- ing off its tremulous radiations. The eruption had ceased that morning, but a volume of smoke was still emitted, which the strong northeast wind swept down in a trailing current along the tree-tops. '• The cone was patched over with yellow, crystallized sulphur, deposited from the hot vapors passing up among the loose stones. Tlie trees all around were stripped of their limbs, leaves, and bark, and resemljled so many giant skeletons. Tempted by the quietude of the volcano, and anxious to inspect it more closely, in spite of the entreaties of our guides, we descended from our position, and going to the windward scrambled over the interven- ing lava beds, through patches of thorny cactuses and agaves, toward the cone. On all sides we found the flakes VOLCANOES OF CENTRAL AMEIUCA 151 •t '.' of nielted inutter wliirli luid been thrown out on the first day of tliu orii[)tioii, and which had moulded themselves over whatever they lell upon, ^ye had no ditliculty in reaching the base of the cone, the wind driving oft" the smoke and vapors to the leeward. It was i)erhaps a hun- dred and fifty or two hundred feet high, by two hundred yards in diameter at the Ijase, and of great regularity of outline. It was made up entirely of stones, more or less rounded, and of every size from one pound up to live hun- dred. No sound was heard when we reached it, except a low, rumbling noise, accompanied by a slight tremulous motion. Anxious to examine it more closely, and to tost the truth of the popular assertion that any marked dis- turbance near the volcanic vents is sure to bring on an eruption, we proceeded to ascend. Fearing we might find the stones too much heated near the summit. I i)repared myself with two staffs, for support, and to save my hands; the doctor disdained such appliances, and started without them. The ascent was very laborious, the stones rolling away beneath our feet, and rattling down the sides. We, however, succeeded in almost reaching the sunnnit, when Dr. Livingston, who was a little in advance, suddenly recoiled with an exclamation of pain, having all at once reached a layer of stones so hot as to blister his hands at the first touch. We paused for a moment, and I was looking to my footing when I was startled by an exclama- tion of terror from m}- companion, who gave simultane- ously an almost superhuman leap down the side. At the same instant a strange roar almost deafened me ; there seemed to be a whirl of the atmosphere, and a sinking of the mass upon which i was standing. Quick as thought I glanced upward ; the heavens were black with stones. 1 152 VOLCANOES OF NOUTH AMKKICA \\\ n and a thousand lightnings flashed among them. All this was in an instant, and in thu same instant I too was dasliing down the side, reaching the bottom at the same moment as my companion, and just in time to escape the stones, which fell in rattling torrents where we had stood a moment before. . . . The eruption lasted for nearly an hour, interspersed with lulls, like long breathings. The noise was that of innumerable blast furnaces in full operation, and the air was filled with projected and falling stones. ..." For several months after the eruption just described as stated by Squier, no eruption occurred, with the exci!i)tion of one on May 27, which followed the falling of tlmjin^t consklerahle shower of rain. The fact that an eruption followed the rain may have been a coincidence simply, but is suggestive, in connection with what is known concerning the part played by water in volcanic eruptions. In order to bring the records of the young volcanoes of the North American continent into one group, wo will borrow from a chapter in advance, which deals with the volcanic records of Mexico, an account of the birth of what is now an imposing mountain, known as Jorullo. Jorullo, Mexico. — Jorullo, frequently cited as a volcanic mountain that was upraised in a single night, is situated about 170 miles westward of the city of Mexico. Its fame is due largely to the account of its origin and early history given by Humboldt,^ who visited it fifty-six years after its birth. In spite of the veneration we feel for the writings of 1 A. von Humboldt, " Political Essay on the Kingdom of Xew Spain," translated by John Black, London, 1811, Vol. 11. pp. '211-223. See also " Cosmos," translated by Otte and Paul, Xew York, 1809, Vol. V. pp. 2!»;5, 291, 297-301. VOLCANOKS OK rKNTKAL AMKKICA l.")3 t\w immortal IIumltoMt, one is inolinod. on reiulim^ his accoiiut o. Jorullo, to ([iiostion tlui autlicntioity of tliu in- formation on which ho l)asos his very graphic description. As stated by Ilumholdt, th(; acconnt of the remarkable occnrrence referred to, was snni^' in hexanu.'ter verses by the Jesnit P'atiier Raphael Landivar, a native of Guate- mala, and also recorded by the Abl)e Clavigero, in an an- cient history of his country ("Storia antica di Messico"). These writings, which it does not seem should be con- sidered as possessing scientific accuracy, and the narratives of persons who Avitnessed the catastrophe, gathered over half a century after its occurrence, are the sources of the information on which Humlxjldt's fref[uently quoted de- scription of the event are based. While the main features of the eruption given below may apparently l)e taken as approximately correct, many of the details are apparently exaggerated. The theory held by Humboldt, that volcanic craters are formed by the npheaval of the earth's crust, "crater of elevation," possibly influenced his interpretation of the reports of the eruption narrated to him. The ac- count of the birth of Jorullo given )jy Humboldt in his essay on New Spain, but somewhat abbreviated, is as follows: Jorullo, it is said, was formed in the night of September 29, 17")0. Humboldt and Bonpland visited it and gained its summit in 1803. The plaJn on which Jorullo stands is elevated 750 to 800 metres above the sea and is surrounded In' volcanic rocks. For some time previous to the date of the eruption just given, the middle of the plain was occupied by fields of sugar-cane and indigo. These fields belonged to the plantation of San Pedro de Jorullo. In the month of June, 1750, subterranean noi.ses of an alarm- ing nature were heard, accompanied by earthquakes, which I \ f ! ir.t VOLCANOKS OK XOUTII AMKKKA I! Hh i i: .succcL'dud OIK' Jinotlii'i- for lifty or .sixty days. From tlu^ hcgiiuiin.L!; of ScjjliMJilx'r, liowover, until tliu tinic of the tTuptioii, tr!iii(|uillity .st^cMiK^l rostored, l)iit in IIil' iii^ht Ijctween SeptendnT 28 and 29, tlio subtorraiiuau noises recommenced. '•The at'frightcMl inhabitants 11(^(1 to the mountains of Agnasarco. A tract of ground from three; to four .s(|uare miles ^ in extent, which goes hy the nana; of Jfa/jjaj/s, ro.se lip in the sha[)e of a bladder. The bounds of this convulsion are still distinguishalde in thefraetural strata. The MuljKUjs [answering to the aa hiva, surfaces described on a previous page], near its edge, is only twelve metres above the old level of the plain called the jjlat/as from a chasm, of which the direction is from N.N.E. to the S.S.E. This is the j)henomenon of the Montenovo of Naples, .several times re[)eated in a ran^e of volcanic hills. The most elevated of these enormous masses, which bears some resemblance to the /jifj/s de I'Auvergne, is the great Volcan de Jorullo. It is continually burning, and has thrown up from the north side an innnen.se (piantity of scorified and basaltic lavas containing fragments of primitive rocks. These great eruj)tions of the central volcano continued till the month of February, 1700. In the following years, they became gradually le.ss frequent. . . . The roofs of the houses of Queretaro were then covered with a.shes at a distance of more than forty -eight leagues in a straight line from the scene of the explosion. Although the subterraneous fire now appears far from violent, and the Mfifjj(ti/s and the fjreat volcano bei?in to be covered with vegetation, we nevertheless found the ambient air heated to such a degree by the action of the small ovens [hornitos], that the thermometer at a great distance from the surface and m the shade rose as high as 43° C." In the bot- tom of the crater, temperatures of 58° and 60° C. were ■ »l— WlUx W f W Ili, - }\ IMAGE EVALUATION TEST TARGET (MT 3) 7 m 4 %' w/ i.O I.I 12.8 ■30 1^ ■tt m 12.2 ^ 1^ 12.0 IL25 Hgu K 1.6 '/I ">!^.'*' ^>. f^ -si^^ ^5. •*X5i^ '/ Hiotographic Sdeiices Corporation 23 WfST MAIN STREET WEBSTER, N.Y. 145M (716) V2-4503 •^^ .,^' < 4^ ;^%> >^^ '/j m w M ^v ^■A,'isSii-,. , i 1 15)) VOLCANOES OF NORTH AMERICA i 1 obtained. Fissures from which sulphurous vapors were escaping were found to have a temperature of 85° C. There is much more in the narrative of Humboldt n'lating to the new volcano, but I doubt its value when considered in the light of modern science. Al- though the main facts secured are seemingly correct, the student of volcanic phenomena will, I think, take exceptions to many of the details reported by priests and Indians, and also to the interpretations of these reports by Humboldt. The four young volcanoes described in th.e la.«t few pages are of great interest as showing the nature of the phenomena that attend the formation of new volcanic vents, n, however, we consider a volcano as the sur- face manifestation of an opening or conduit, leading down to a central rey-ion of intense heat in the lower portion of the earth's crust, it seems doubtful if we should consider the examples cited as new volcanoes in the strict meaning of the term. In each case, the out- break of steam, lava, etc., has been in a volcanic region and in the immediate vicinity of dormant or extinct craters, It would seem rather that old passageways have become closed and the imprisoned steam generated by water coming in contact with highly heated rocks, or the effects of renewed pressure on the reservoirs deep below the surface, has led to the opening of new vents alon^r a line of ancient fracture. Older Volcanoes From the numerous and, for the most part, popular accounts of the volcanoes of Central America that have been published, it i° impossiijle to select sufficient well- VOLCANOES OF CENTRAL AMERICxV 157 . authenticated data tu enable one to conii)ile an adequate history of the igneous mountains of that region. The facts in hand show that about thirty volcanoes have been more or less active within historic times. These are indicated on the list already presented. Him- dreds of craters that have ceased to emit molten lava, scoria, lapilli, etc.. still discharge steam and sulphurous vapors, and may, therefore, be classed as solfataras. Throughout the volcanic belt, hot springs are numerous, which no doubt, in most instance.^, owe their high tem- perature to the heat of volcanic rocks below the surface, but these have received little scientific attention. In this region, also, earthquakes have been of frequent occurrence and, in some instances, intimately associated with volcanic outbursts. Among the rocks in the volcanic region mentioned by travellers or described by the few geologists who have studied them, basalt is of limited occurrence. The moun- tains are composed principally of trachytic rocks, and the country over large areas is deeply covered with lapilli, pumice, dust, etc., which record the energy of explosive volcanic eruptions. It is the decay of these fragmental products especially, under the influence of tropical rains and a high temperature, that gives to much of Central America its wonderfully rich soils. Instead of attempting to assemble all the available data relating to the older volcanoes of Central America, I shall select a few of the most typical examples of volcanic eruptions and of volcanic mountains, not alone for their geographical interest, but as illustrations of the life his- tories of volcanoes in general. The examples chosen are Conseguina, Fuego, and Agua. s I: T " ', 158 VOLCANOES OF NORTH AMERICA Conseguina. — Of all the volcanoes on the Ncjrth Ameri- can continent, none have attracted a greater share of attention than Conseguina. It is i)lace(l first among the volcanoes here especially considered, having '" by merit been raised to that bad eminence," on account of its fear- ful eruption in 1835. Previous to the explosion of Kra- katoa in 1883, Con.secjuina, totjether with Sunibawa on the Fir,, (i. Sketch of Conseguina (Dollfus and Mont-Serrat.) island of Sumatra, served as the best example of volcanic explosion on record. Conseguina is situated on the Pacitic coast of Nicaragua, and forms the principal elevation of a peninsula which projects from the mainland towards the northwest and partially shuts off the Bay of Fonseca from the sea. The volcano is now extinct or dormant. From a distance it presents the appearance of a truncated cone, with an ex- treme elevation above the sea of a little less than four thousand feet. When more closelv examined the low VOLCANOES OF CENTRAL AMERICA 150 mountain i.s found to contain a comparatively large crater- like depression in its summit. Of the ap[)earance of Conseguina previous to its now historic eruption in 18o5, there seems to be no authentic record. At tiiat time the summit of the mountain, which had been formed l)y material ejected during previous eruptions of a milder cliaracter, was literally blown away, and the rocks composing it reduced to fragments and distributed far and wide over the adjacent sea and land. By extending upward the sides of the truncated cone now remaining, an approximate restoration of the form of the original mountain may be made, which indicates that its height was in the neighborhood of 8000 or 10.000 feet. This estimate, however, would be approxi- mately correct only in case the mountain had been formed by comparatively mild explosive eruptions. It may have been truncated by violent explosions, previous to the one of which we have a record. The appearance of Conseguina as seen from the sea is shown in the accompanying sketch, copied from Dollfus and Mont-Sorrat.' The crater within the truncated cone has a diameter of four miles and a depth below the high- est point of its rim of three hundred feet. Of the many accounts of the eruption of Conseguina that have been published, the most graphic as well as the most accurate, so far as I can judge, is one compiled by Sc|uier,^ about fifteen years after the occurrence. This account reads as follows : ' A. Dollfus et E. de ^loiit-Serrat, "Voyage geologiciue dans les repub- liqiies de (iiiatemala et (if Salvador," Paris, 1808. - E. G. Squier. "On the Volcanoes of Central America," American Asso- ciation for the Advancement of Science, Proceedings, Xew Haven meeting, 1850, pp. 107-109. 1 'n wsmm 1(]0 VOLCANOES OF NOUTH AMERICA !''!'• ■:f * ' I !• i- '• On the morning of the 20tli of Janiuiry in that year [1835], several loud explosions were heard for a radius of a hundred leagues around this volcano, followed by the rising of an inky black cloud above it, through which darted tonrhicli there exists, are grass covered. 170 VOLCANOES OF NORTH AMERICA /: IT I* •: I' I The name of this charming mountain, Volcan de Agua, or water volcano, has led some persons to suppose that it is a volcano which erupts water ; while others state that snow on its sides is sometimes melted by the heat from within, and descends in floods into the neighboring valleys. We are assured by Dollfus and Mont-Serrat, however, that neither of these explanations is correct. The origin of the name is this : at the time of the Spanish invasion, the crater at the summit of the mountain contained a lake, which was supplied by rain. In 1541, as the result of an earthquake, the wall of the crater on the northeastern side gave way, and an immense volume of water poured down the mountain side, carrying with it earth, rocks, and trees that obstructed its course, and overwhelmed a village which had been built by the Spaniards on the site where to-day stands the town of Ciudad Vieja. The present condition of the mountain confirms this account, which Las been derived from historical records. The crater presents all the characteristics of a former lake basin, and upon the side of the mountain an immense ravine can be clearly seen, departing from a place where the rim of the crater is broken, and extending in the direction of Ciudad Vieja. The soil of the valleys near the base of Agua is de- scribed in the book we are citing, as being composed of layers of white pumice, yellowish cinders, black lapilli, and violet sands. No traces of lava flows were found. On the lower slope of the cone, where the ground has an inclination of from 28° to 30°, the fertile soil contains pumice and scoria, with a good proportion of yellow clay. At an elevation of 2664 metres, in an opening cleared in the dense forest, the soil was found to consist of a thick VOLCANOES OF CENTRAL AMERICA 171 layer of decayed volcanic sands and black lapilli in small fragments. The vast abundance of material such as is ejected during explosive eruptions, and the absence of lava flows, as well as the character of the crater walls, which are also of fragmental products, show that Agua, during its days of activity, was a volcano of the explosive type. Its perfection of form is no doubt due to its having been built by the accumulation of projectiles shot into the air, and falling about their place of egress. The eruptions were probably never sufficiently violent to blow away the summit of the cone, and, so far as known, no breaks in its sides led to the formation of dikes. Its grace and sym- metry indicate that it was built up by long-continued but comparatively mild, explosive eruptions. CHAPTER IV i: VOLCANOES OF iMEXICO The distribution of the better known volcanoes of Mexico ia shown on Plate 4. Humboldt states that the only volcanoes m Mexico that have been active within historic times are Tuxtla, Popocatepetl, Jorullo, and Colima, but this list has been somewhat extended since he wrote. The geology of Mex- ico is still but imperfectly known. Travellers report many craters and mountains besides those just mentioned, that are of recent date, and also extensive lava fields and vast deposits of lapilli and volcanic dust, which are the last additions made to the soil over broad regions. The narrow belt of fractures and faults, with their ac- companying volcanic phenomena, which is such a pro- nounced feature in the geology and geography of Central America, is continued into Mexico with a marked increase in breadth. In south-central Mexico the volcanic belt broadens until it touches both the Gulf and Pacific coasts. Accompanying this increase in width is a decrease in the number of active craters, and a diminution in their inten- sity. All of the still active volcanoes are confined to the region south of latitude 22°; that is, they are situated south of an east and west line, crossing the Republic about 200 miles north of the city of Mexico. The best accounts of the physical geography of Mexico that have come under my notice, are in the well-known 172 T \ fF VOLCANOES OF MEXICO 173 writings of Humboldt, and in the recently published vol- ume entitled •' North America," by Reclus.' Descriptions of Mexican volcanoes, in most instances of a popular char- acter, have been given by numerous travellers and by Spanish priests. In a few instances definite and reliable observations have been made by members of scientific ex- peditions ; among these, the ones that have been found of most assistance are those published by the Geological Sur- vey of Mexico. From this varied store of information, I have selected such facts as will assist the student in grasp- ing the leading characteristics of volcanoes in general, and, at the same time, furnish information concerning the physical geography and geology of Mexico. Orizaba. — This reuiarkably regular and beautiful sym- metrical mountain is situated in the eastern part of Mex- ico, and a little south of a straight line joining the city of Mexico and Vera Cruz. It is about seventy-five miles west of Vera Cruz, and in sight from that city. Orizaba derives its present name from the city of Orizaba, near which it rises, and is known also by its ancient Aztec name, Citlal-tepetl, or Star Mountain. Its elevation is approximately 18,200 feet. For a time it was consid- ered the highest summit in North America, but is now known to be surpassed in elevation by Mt. Logan (19,500), situated in northwestern Canada, near the Alaskan bound- ary. Triangulations made by Ferrer in 1796 placed the height of Orizaba at 17,879 feet. Humboldt, by similar methods, but, as he states, under unfavorable conditions, found it to be 17,375 feet.- Recent measm^ements by 1 filisee Reclus, " The Earth and its Inhabitants : North America." Edited by A. H. Keane, New York, 1891, Vol. II. 2 " Cosmos," New York, 1869, Vol. V, p. 239. \\: \ f t I! ii ! 174 VOLCANOES OF NORTH AMERICA means of an aneroid barometer, gave an elevation of 18,205 teet.^ Orizaba rises from a forested region and reaches the lower limit of perpetual snow, but no glaciers have been reported to occur about its summit. The upper limit of forest growth, or the " timber line," is at an elevation of about 12,000 feet. Above that elevation the rocks are bare until the snow that usually covers the summit is reached. At the summit, there are three craters, separated one from another by ridges of lapilli. The shapes of these depressions show that but little erosion has taken place since the eruptions that gave them their forms. The last observed eruption is stated to have occurred near the mid- dle of the eighteenth century. The igneous energy that built the mountain is now extinct or dormant, and the craters are normally occupied by snow. Like Mt. Etna, and many other isolated volcanic mountains, Orizaba is surrounded by eruptive rocks, and its flanks studded with numerous cinder cones and craters of small size. Much of the lava surrounding it came from its own eruptions, and some of the secondary cones are evidently parasitic ; * The elevations of four of the higher volcanic mountains of Mexico were measured by Professor Angelo Heilprin in 1889 (Philadelphia Acad. Nat. Sci., Proc, 1890, pp. 251-2G5) by means of an aneroid barometer, and the following results obtained : Elevation of Orizaba, 18,205 feet above the sea. " Popocatepetl, 17,523 " " " « " Ixtaccihuatl, 16,960 " « " « " Nevado de Toluca, 14,954 " " " " These results differ considerably in each instance from previous measure- ments, and, on account of the method employed, cannot, in the opinion of men well qualified to judge of such matters, be considered as more than approximately accurate. The possible error in each case may be as great as five hundred feet. VOLCANOES OF MEXICO 175 that is, they owe their origin to tlie escape of steam from the lava flows on which they are located, and do not indi- cate the presence of vents connected with conduits leading to deeply seated regions of heated rocks. Other crater and lava flows apparently owe their origin to the opening of fissures in the sides of the mountain, which ucave e^rress to lava and steam derived from the main conduit of the volcano. The summit of Orizaba was first reached by Reynolds and Maynard, who were connected with the army of the United States which invaded Mexico in 1848. Since that time several ascents have been made. One of the latest of these was by an expedition sent out by the Academy of Natural Science of Philadelphia, in 1889, in charge of Heilprin. From an account of this ascent the following notes have been taken : ^ The starting-point for the ascent was San Andres, a railroad town about midway between the city of Mexico and Vera Cruz. San Andres has an elevation of about 8200 feet. About the town there is a desert of sand, scantily clothed with aloes, cactuses, and yuccas, with here and there a cherry, oak, and an apple tree. To the east- ward of San Andres, and barely twenty-five miles distant, rises the truncated cone of Orizaba, and its twin neighbor Sierra Negra ; to the west and south are numerous vol- canic cones, with elevations varying from 300 to 500 feet above the arid lands surrounding their bases. At an elevation of about 1000 feet above San Andres, the exploring party left the dreary, open country with its * Angelo Heilprin, " Among the World's Highest Mountains : an Ascent of Orizaba, Mexico." In " Around the World " (a magazine published in Philadelphia), Vol. 1, 1894, pp. 21-:^6, 49-53, with illustrations. 176 VOLCANOES OF NOllTII AMERICA ■I I I " t r \ ;l li ! defert vegetation, and entered a region of pines. The species of pine that is most ahundant in the lower portion of the forest belt is the long-leaved T'lnus Montezuma (var. macrojjJu/Ua). This tree is found, seemingly, on the slopes of all the giant volcanoes of the Repul)lic, asso- ciated more or less Avith a closely related form, the Pinus psemlostrohiis, and with Phms Teocote. The Montezuma pine grows also in the neighborhood of the town of Orizaba, at an elevation of 4500 feet ; and on the south- west slope of the volcano of Jorullo, where it descends to 4000 feet. It flourishes side by side with the palmetto in the transition zone which unites the vegetation of the lowlands with that of the uplands. This pine is of stately presence. Its shaft is frequently a hundred feet or more in height, and grows in open ranks with little or no under- growth. On the lower slopes of Orizaba, Heilprin says : '' We wander through a dense park, into which vistas of rare beauty open up at almost every point. Here the dis- tant valley unfolds itself a boundless panorama; there the majestic cone of Orizaba, white with the frost of ages, towers far into the region of eternal cloudland." At an elevation of between 10,000 and 10,500 feet, a belt of spruce trees [Abies religiosa) was entered, but, on its lower margin, oaks had already begun to appear. The pine, however, still continues to be the dominant form of arborescent vegetation. Flowering plants were not spe- cially numerous, the most noticeable being a lupine and several species of senecio. At an elevation of about 12,000 feet, the forests terminate, and a broad, open, grass-covered belt encircles the cone below the lower limit of perennial snow. The divide between the Sierra Negra and the peak of VOLCANOES OF MEXICO 177 Orizaba offers a splendid view of each of these volcanoes. The former barely reaches the line of perpetual snow, and shows well the effects of long-continued atmospheric erosion ; the latter, white with frost, retains the con- tours which were impressed upon it at about the time of the last eruption. At various places on the flanks of Orizaba dark buttresses of rock stand out in vertical masses, showing where eruptions of greater or less mag- nitude have marked epochs in the history of the mountain. Huge outwellings of lava seam the slopes in radiating lines, but they belong in great part to a period of volcanic activity when the centre of eruption was located some little distance from the site of the present crater. At an elevation of 14,500 to 15,000 feet, the zone of grasses terminates with an irregular edge. With the grasses are a few flowering plants. The last traces of terrestrial animal life occur at about 15,000 feet, where, Heilprin says, " we picked up a soli- tary lizard from one of the sun-warmed boulders. There were no msects, at least we failed to find any traces of their existence, at this altitude. But birds were still observed and heard above us ; we thought we recognized the tit and the chickadee, and possibly a species of wren. There was no question as to the raven, whose ' caw ' was heard far o'ertop of us, or the sparrow-hawk. At about one o'clock we reached the ice-cap [elevation 15,500 feet], which is here split by a ridge of rock and boulders enter- ing far into its limits. . . . The snow field, or more cor- rectly ice field, was of inconsiderable development, at no point when seen by us attaining a greater thickness than about 5-7 feet. Its surface was everywhere cut up into sharp pinnacles (seracs) two or three feet in height, which, I 4 i 178 VOLCANOES OP NORTH AMERICA (; I i i wliilo (^fT((ring safe lod^ornont to tlio feot, rendorod progress exceedingly irksoine. There was no soft snow, and the feet made Init little impression on the crusty surface of the ice." In ascending Orizaba when the sky is clear, magnifi- cent views are obtained of the great tableland of central Mexico on the west, and of the shore of the Gulf on the east. As described by Heilprin, at an elevation of 15,000 feet, the lofty sunnnits of Popocatepetl and Ixtaccihuatl came into view, through the haze, although one hundred miles or more distant, and were boldly outlined against the western sky. As in most high mountains, however, the truly picturesque scenes are to be observed from the lower slopes. Views from lofty summits resemble maps rather than pictures. In comparison with many other mountains of similar height, Orizaba is easy of ascent. The height of the tim- ber line, 12,000 feet, leaves but GOOO feet above the high- est camp fire. The elevation above the point at which a camp can be established, furnishes a rough measure, in many instances, of the difficulties to be overcome in mountain climbing. Heilprin states that from bottom to top, there are no precipices to climb, no impending ledges to crawl around or over, and no glaciers to cross. In these respects Orizaba agrees with Popocatepetl, while it differs greatly from Ixtaccihuatl. "The slope from the plateau base to the summit is pleasingly gentle and uni- form, and the traveller who is bent upon making the attack requires merely a staff, proper foot gear, and a good constitution." Popocatepetl. — The second mountain in Mexico in reference to altitude is Popocatepetl, or the Smoking ■^ VOLCANOES OF MHXICO IT'.t Mountain. Triangulations made by Ilinnltolclt ' in 1S04 gave 17,728 feet, wliile aneroid ineasurenienLs by Ileil- prin- in 1889, already referred to, gave 17,0-;} feut as the lieigbt of the summit. M(jre reeent measurements by tlie Mexican Geological Survey' place the elevation at 17,870 feet. For many years Popocatepetl was thought to he the highest mountain in North America, hut it is now known to be surpassed by at least three other peaks on this continent. Popocatepetl is a conical peak with a depression i)Y crater in its sunnnit. On the rim of the crater there are two prominent crags, connected Ijy a narrow ridge ; the higher of these is known as Pico Mavor. and the other has been named Espinazo del Diablo. The bottom of the crater is 1056 feet below the summit of the highest spire on its rim; the surface diameter of the great bowl is about 2000 feet. From fissures in the bottom of the crater steam still escapes, but the heat is not sullicient to melt the winter's snow, which reaches a depth oi eight or ten feet, and covers the outer slopes of the mountain down to an elevation on the north side, of 14, '^08 feet. A thousand feet below the snow line is the upper limit of vegetation. All of the lower slopes are clothed with forests, which in places attain a tropical luxuriance. The melting snows supply a small lake in the crater, and the water percolating through the porous lava-sand feeds copious thermal springs about the base of the mountain. 1" Cosmos," New York, 1869, Vol. V, p. 127. 2 Philadelphia Acad. Nat. Sci., Proc, 1890, pp. 251-20;j. 'J. G. Aguilera and E.Ordonez, "Expedicion cienti'tica al Popocatepetl," Mexico, 1895. / 180 VOLCANOES OF NOUTH AMEUICA t.l ! I'll t i!^ A. Tliis percolation of moteoric water tli rough the rocks, illustrates one t)f the important [)rocess(»s by which a volcanic mountain parts with its heat. ro[>ocatepetl stands on the eastern edge of the great central plateau of Mexico. On one side it looks down on the capital of the Republic, and on the other descends into the tropical lowlands bordering the central plateau. The visual height, as seen from the city of Mexico, is 10,00(1 feet ; and from the lowland to the eastward, about 17,000 feet. Seen from the basal plains, it sweeps up in one grand curve to nearly its full height, — a colossus of three and a quarter miles in elevation, white with ever- lasting frost on its summit, and bathed in the green of palms, bananas, oranges, and mangoes at its Imse. Ever- green oaks and pines encircle its middle height, and above them, l)efore the ice itself is reached, occur broad areas of loose sand into which the lavas have been changed by weathering. Soft wreaths of sulphurous vapor may at times be seen curling over the crest of the summit crater, — gentle reminders that the days of volcanic activity are not yet necessarily over. The ascent of Popocatepetl, as stat-^d l)y Ileilprin,^ is neither a difficult or dangerous task. One or more as- cents are probably made each year. Horses can mount without much difficulty to an elevation of 13,000 or 14,000 feet, and might be urged still higher. The view from the summit is almost incomparably grand, reaching on clear days from the Gulf of Mexico almost to the Pacific. In three directions the view is unbroken except by the limitations of vision ; on the fourth (to the north) * "Around the World" (a magazine published in Philadelphia), Vol. 1, 1894, p. 13, with a fine illustration. 1 ; i ^p VOLC/VNOES OF MKXKMJ 181 it om])raroa a colossus of nearly tlio saino Ijoi^lit as the great " vSmokinj;; Mountain" itself, the famous Ixtaccihu- atl, or " White Woman." AlihoUjL^h rising fully oOOO feet above the snow line, its snowy covering is inecMisiderable ; ranjly (lo(>s it meas- ure more than three to six feet in depth. Nothing worthy to be considered as a glacier is found on the mountain. Many a.scents of Popocatepetl have been made not only by travellers, but by volcaneros, who gather sulphur from the crater. It has been estimated that about fifty tons of sulphur are obtained annually, the supi)ly being re- newed by condensation from escaping vapors. The crude methods heretofore employed to gather and transport tliL* sulphur, arc to be sup[)lanted, it is said, Ijy mure en- lightened processes, under the management of a syndicate. In 1895, a short account was published of a scientific expedition to Popocatepetl, by the Mexican Geological Survey,' which adds nuich to the geological history of the mountain previously recorded. The crater is described by the explorers just mentioned, who spent twenty-eight hours in examining it, as ellip- tical in outline, with sloping walls, and with axes measur- ing G12 and 400 metres, respectively. Owing to marked irregularities in the height of the rim of the crater, its depth may be variously stated. Its bottom is 505 metres below the summit of the highest pinnacle, Pico Mayor, and 205 metres below the lowest point on its rim. "Popocatepetl is a cone formed by an accumulation of many successive currents of lava, covered with fragmen- * J. G. Aguilera and Ezequiel Ordonez, " Expedicion cientifica al Popo- catepetl," pp. 1-48, PL 1-G. The notes here quoted are from an abstract of the report printed in the "American Geologist," Vol. XVII, 1890, pp. 330, 331. I h'i I i I $ ^i- w* w 182 VOLCANOES OF NORTH AMERICA tary materials, stones, sand, ashes, etc., and corresponds to those volcanoes called by some geologists ' stratified cones.' The lower or older of these currents shows a rock structure more granular and less lustrous than that of the later ones. Polarized light also reveals a crystal- line development in the former, which is not found in the more glassy and amorphous structure of the latter. From these and other facts, the authors deduce the conclusion that the history of the volcano has been marked by three stages, which they denominate penodo cinerorjeno, ^;c;70f/o brechofjoio, and ijerlodo Idvico. The earliest, the lava period, was the lon,G:est ; during the second, the ejecta consisted largely of pumice, mixed at times with volcanic bombs — blocks of andesite of the same nature as the lava; the third has supplied showers of ashes, which overlie the older products and have been much eroded by winds and rain. These periods the authors correlate with the Plio- cene, Pleistocene, and Recent. Some of the earlier ande- site lava flows are buried beneath beds containinuj remains of the horse and elephant, while a stream of very liquid basalt from the neighboring peak of Xitli overlies not only deposits containing vertebrate fossils, but even hu- man remains. "Three kinds of eruptive matter are defined, — labra- dorite-basalt, hypersthene-andesite, and trachyte, of which the first is the oldest, and is found in the lowest currents ; but the grand cone is mostly composed of the second, which varies in structure from holocrystalline to vitreous, while the little summits consist of the third kind of ejecta. "In the various facts given, the authors see a record of the original great energy and gradual decay of the vol- VOLCANOES OF MEXICO 183 canic action which has now ahnost ceased, nothing but smoke and vapor issuing from the cone." As stated by Rechis,' there are reasons for believino" that the first person who ascended Popocatepetl was the Spanish captain, Diego de Ordaz, who was with Cortes in 1519, but authorities are cited which render it uncertain tliat he gained the summit. Ixtaccihuatl. — Rising to the north of Popocatepetl, and, like its greater neighbor, in full view from the city of Mexico, stands Ixtaccihuatl, or the "White Woman," as the mountain was named by the Aztecs. The sum- mits of these two giant peaks are barely len miles apart. The description of an ascent of Popocatepetl, already cited, would apply in all its general features to its near neighbor, and need not be repeated. The height of Ixtaccihuatl is given by Heilprin as 16,960 feet, but other measurements, whicli so far as can be judged are equally trustworthy, make it some 500 feet less. Some writers have asserted that this grand peak is not of volcanic origin, but fail to give reasons for considering it to have a different history than the neighboring volcanoes, which it closely resembles. Its conical form and the fact that it is largely composed of trachytic rocks, seem to show that it owes its promi- nence to volcanic agencies. It is evidently older than Popocatepetl, and has undoubtedly been decreased in height by erosion. There is no crater at the summit, and no evidence of lingering volcanic heat. The sum- mit is snow-capped even in summer. The original crater may reasonably be supposed to have been filled by the ^ jfilisee Reclus, "The Earth and its Inhabitants: Morth America," New York, 1891, Vol. II, p. 27. '% 1 1' 184 VOLCANOES OF NORTH AMERICA '{ ^1 • I I • Y i U 1 I il I i washing in of its sides, and the summit angle of the peak bhmted by the same process. Xinantecatl. — Al^out forty miles southwest of the city of Mexico near the city of Toluca, rises a symmetri- cal volcanic pile with gentle slopes, to a height of about 15,000 xcet, which is known as Nevado de Toluca, or the "Snow of Toluca." Its Aztec name is Xinantecatl, or the " Naked Lord." The summit of Xinantecatl, as seen from the south, barely reaches the lower limit of perpetual snow, but its northern side is v/hite, even in September and October, the months when the melting and evaporation of the snow is most advanced. In the summit of the peak there are two craters, which are now flooded and form lakes of fresh water, with a combined area of about eighty acres. The larger lake is reputed to be thirty feet deep and inhabited by fish of a peculiar species. Xinantecatl furnishes an example of an extinct or dormant volcano, and serves to connect in one series certain older volcanoes like Ixtaccihuatl, which have been exposed to storms and frosts for such a length of time that their craters have disappeared, with volcanic moun- tains of recent date like Popocatepetl, which not only still retain their summit craters but are yet giving out steam and heated gases. Tuxtla. — Volcan de Tuxtla, situated on the coast of the Gulf of Mexico, about eighty miles southeast of Vera Cruz, is reported to be ^.950 feet high. In 1664, it erupted molten lava, but again became quiescent, until March, 1793, when one of the grandest volcanic outbreaks of modern times occurred. This eruption was of the explosive type, and rivalled in energy the catastrophe that I ^i^ VOLCANOES OF MEXICO 185 blew away the summit of Conseguina in 1835. Scoria, lapilli, and dust were blown into the air with such violence that they rosn thousands of feet and were carried by the wind 150 miles towards the northwest, and about the same distance to the southwest. The roofs of houses in Vera Cruz, Perote, and Oaxaca were covered with lapilli and dust. The noise of the explo- sion sounded like heavy guns and was heard distinctly at Perote, about 150 miles to the northwest. Suice the great eruption just referred to, less violent discharges from the same vent have taken place. The small height of Tuxtla is due to the blowing away of the summit of the mountain during a great explosion in 1793, and illustrates the fact that young and energetic volcanic mountains are not necessarily lofty. Mild explo- sions, if long continued, tend to build up symmetrical peaks with gracefully curving slopes, but when the energy of the explosions increases, the summits of the volcanoes in which they occur are frequently blown away, and the fragments distributed far and wide over the adjacent region. Low mountains with abnormally large craters are the results of such catastrophes. In fact, when the explosions are excessively violent, nothing to suggest a mountain remains, but great pits in the earth without elevated rims sometimes result. This is forcibly illus- trated in the case of Krakatoa in 1883, already described, when not only was a mountain blown away, but a depres- sion 3000 feet deep left to mark its site. It does not follow, however, that all large craters, "calderas," and " crater-rings," are to be accounted for in this manner, as the drawing off of the liquid lava from a crater and the tumbling in of its walls may produce similar results. ^T :!j !. II H V Ml' . \ l|[' I 186 VOLCANOES OF NOUTH AMEIIICA Cofre de Perote. — About thirty miles north of the peak of Orizaba, there stands a mountain about 13,552 feet high, with a quadranguhir summit. When seen from the neigliboring portion of the Gulf of Mexico, the sum- mit of the peak has a resemblance to a coffer, or sar- cophagus, which has suggested its modern name. To the Aztecs it was known as Nauhcampa-tepetl, or " Four- ridged Mountain." Surrounding the base of the moun- tain, and evidently originating from it, is a deposit of lava and pumice, which gives the country an uneven surface, and has gained for it the name malajxiis or "bad country." This term is used in several parts of Mexico for rugged lava flows and has been adopted somewhat generally by American geologists as a technical name for lava sheets with rough surfaces composed of angular blocks of rock, similar to the aa surfaces of the lava streams of Hawaii. The Cofre was ascended by Humboldt in 1804 and its alti- tude and position determined. Nothing of the nature of a crater was found at the summit, but the rock of which the mountain is largely composed is termed a dlorlt'ic trachyte. Streams of hardened lava radiate from the mountain, and record the energy of its ancient discharges. Humboldt found only isolated patches of snow about the summit in the month of February, which reached down to a limit of 12,500 feet, and about 700 or 800 feet below the upper limit of forest growth. The top is bare of snow in late summer and autumn. The Cofre is evidently a volcanic cone that has passed its youth and has yielded, to a marked degi-ee, to the attacks of erosive agencies. To Humboldt it appeared to furnish an example of a mountain upraised by forces acting from beneath and to be a "crater of elevation." r VOLCANOES OB" MEXICO 187 This hypothesis to account for the origin of volcanic mountains has for the most part been abandoned, for the reason that it is now well known that volcanoes build up elevations by extruding lava and by blowing out projec- tiles which accunudate about the opening from which they came, but not by pronounced upheaval of the earth's crust. Humboldt's account of the Cofre is of interest as illustrating his hypothesis of the origin of volcanic moun- tains by upheaval, as well as for the observed facts it con- tains. He says ^ : " In ascending the mountain I saw no trace of the falling in of a crater, or of eruptive orifices on its declivities ; no masses of scoria), and no obsidians, pearlites, or pumice-stones belonging to it. The blackish- gray rock is very uniformly composed of much hornblende and a species of feldspar, which is not glassy feldspar (sanidine) but oligoclase ; this would show the entire rock, which is not porous, to be a dioritic trachyte. I describe the impressions wdiich I experienced. If the terrible, black lava fields — malapais — (upon which I have here purposely dwelt in order to counteract the too one-sided consideration of exertions of volcanic force from the interior) did not flow from the Cofre de Perote itself at a lateral opening, still the upheaval of this iso- lated mountain, 13,553 feet in height, may have caused the formation of the Loma de Tobias [the flat-topped summit rock from which the mountain derives its name]. During such an upheaval, longitudinal fissures and net- works of fissures may be produced far and wide by fold- ing of the soil, and from these molten masses may have poured directly, sometimes as dense masses, and some- times as scoriaceous lava, without any formation of true »« Cosmos," New York, 1869, Vol. V, pp. 308, 309. I r Hi H I* i ■ i" til I H 188 VOLCANOES OF NORTH AMERICA mountain platforms (open cones or craters of elevation). Do we not seek in vain in the great mountains of basalt and porpliyritic slate for central points (crater moun- tains), or lower circumvallated, circular chasms, to which their common production might be ascribed ? " This is only a portion of Humboldt's discussion of the origin of volcanic mountains, presented in connection with his account of the Cofre, but nowhere does he seem to recognize the clianges that a mountain passes through when subjected to the destructive influence of the atmos- phere. If one has in mind the fact that a mountain with an open crater at the summit may, by erosion, be transformed into a more obtuse cone, or bell-shaped pile, by having the crater walls removed, many of the difficul- ties encountered by geologists half a century or more ago disappear; and a sequence of topographic forms due to volcanic extrusion, and another equally interesting series resulting from decay, disintegration, and erosion, come into view. Colima. — On the west coa^t of Mexico, and bearing much the same relation to the seaport of Manzanillo that Tuxtla does to Vera Cruz, is a volcano known as Colima. As stated by Humboldt, Colima is about 5500 feet high, and at the time of his visit to Mexico, fre- quently ejected lapilli, accompanied by vapor. It pre- sents a fine sight from the town of Colima, from which it takes its name. In winter it is frequently whHened w :th snow. In recent years, Colima has been more active than dur- ing the earlier portion of the present century. Eruptions occurred in 1869, 1872, and 1873. In 1885 lapilli was thrown out and carried by the wind 280 miles to the ^ / VOLCANOES OF MEXICO 189 northeast. Lava was also discharged during these erup- tions, but nearly always from lateral openings, the " sons of Colima " as they are locally termed, and formed small craters on the adjacent plain.' Ceboruco, or Ahuacatlan. — This mountain, with an elevation of about 7140 feet, rises near the Pacific coast, a few miles south of San Bias, and is the most northerly of the recently active volcanoes of Mexico. In 1870, it became violently active, and since then has never ceased to emit steam. The volcano is the centre of a group of craters. Of these there are two of large size and about 1000 feet deep each, one of which still emits steam, but the other is to all appearance extinct.' Volcanoes of Northern Mexico. — To enumerate the remainder of the active or recently extinct volcanoes of Mexico, concerning which general information is avail- able, would necessitate much repetition, and probably lead to confusion instead of serving to illustrate the laws which govern volcanic action. North of the region in south-central Mexico, which is studded with great volcanic mountains and is a direct continuation, but marked by a conspicuous increase in breadth, of the Central American volcanic chain, there are broad fields of rugged lava with a considerable num- ber of craters in various stages of decay and dilapidation. This broader portion of the volcanic belt already referred to, without active craters, belongs geographically with the still broader region of former volcanic activity in the United States and extending for an undetermined dis- tance into Canada, and does not claim special attention at this time. 1 Reclus, "North America," Vol. II, 1891, p. 24. I • ', : I ■ /, I'll ';i H ill il I i I i(J:i lili i A. ( I I i 190 VOLCANOES OF NORTH AMERICA Volcanoes of Lower California. — In the portion of Mexico known as Lower Ciilifornica, volcanic mountains and lava fields also occur ; but in the absence of scientific exploration little need be said concerning them. From various sources I learn that Lower California is traversed from north to south by an elevated region, much of which is composed of volcanic rocks. The highest summits are at the north, where Mt. Calamahue, or Santa Catalina, rises to a height of approximately 10,000 feet and reaches the lower limit of perpetual snow. Midway down the Peninsula, and overlooking the Gulf on the east, stands a group of volcanic peaks known as the Tres Virgenes, which are reported to be from G600 to 7250 feet high. An eruption occurred in this group in 1857, and since then steam has been emitted, some- times in large volumes. I It 1' ilm of ns ic m ;d ih '0 If s P CHAPTER V VOLCANOES OF THE UNITED STATES (Tho distribution of the principal volcanoes of the United Statis is sliown in riate 4.) A GENERAL account of the distribution of the volcanoes of the United States has already been given. It will be remembered that they occur in the Cordilleran region to the west of the meridian of Denver. In the Cordilleran region the surface rocks iirc largely of igneous origin. Nearly every mountain range has an igneous core or has lava sheets or craters associated with it. In several instances entire mountain rantres are composed of rocks that were once molten. The rocks referred to are of all ages, from the Archaean to recent times. It is only to those of volcanic origin, how- ever, and of such a late date that but moderate changes have resulted from erosive agencies, that attention is here invited. The lava flows in numerous instances are still rough and bare of vegetation, and the craters as perfect in outline as when still steaming. It does not seem desirable at this time to attempt a minute description of the hundreds of lava flows and craters within the United States, even if the investiga- tion of this branch of the ancient history of our country was sufficiently advanced to make such a course possible. 191 V '^IH » I' 1 ' 'i < \A m \v: 192 VOLCANOES OP NORTH AMEUICA My plan, thorcforo, will bo to select a few typical ex- amples of volcanic mountains and of lava sheets, for presentation. San Francisco Mountain, Arizona, and Adjacent Craters. — The highest and most prominent group of mountain peaks in the southwestern portion of the United States is in northern Arizona, about twelve miles north of the town of Flagstaff, and known as the San Francisco moun- tains. (Plate G, Fig. A.) The Atlantic and Pacific rail- road passes through Flagstaff, and passengers by that route usually have many fine views of the neighboring mountains, through the open forest of puies that clothes the plateau on which they stand, and extends far up their sides. The highest peak rises 12,562 feet above the sea, and 5700 feet above the general level of the surrounding tableland. The San Francisco group, according to G. K. Gilbert,^ includes a series of large peaks of trachyte, the products of massive eruptions, and a multitude of small scoria cones, associated with broad and, in part, thick sheets of basaltic lava. The larger cones are of comparatively ancient date, possibly Tertiary, and are much wasted by erosion. The summits are sharp, their sides deeply scored with ravines, and nothing to represent a crater remains. Much more recent than the main peaks are the smaller craters of black basalt adjoining them, especially to the eastward. Many of these craters are as perfect as when first formed. The streams of black, scoriaceous lava that escaped from some of them and spread out on the sur- ^ " Geographical and Geological Explorations and Surveys West of the 100th Meridian," Vol. Ill, <' Geology," 1875, pp. 129, 130. \ VOLCANOEa OF TIIK UNITED STATES lOfl ts rounding plain, are so frosli in appoaranco tiiat to an observer looking down on them ironi the sides of the main elevations, they seem scarcely to have cooled from their original molten condition. The number of these recent vents is stated by Gilbert to be some hundreds. As many as one hundred are marked by cinder cones. Sixty-five with craters partially or wholly preserved m.iy be counted. Some of the craters are intensely black, with large areas of dark red where oxidation has taken place, and are entirely free of vegetation ; on others, de.sert shrubs have ascended the slopes, and con- ceal in part the ruggedness of the angular and broken lava and scoria. At least one of the craters contains a lake. A view over this desert of lava studded with craters several hundred feet high, some of which have great gaps in their rims through which floods of molten lava once escaped, calls vividly to mind the illustrations published by Scrope,' of the now classic volcanoes of central France. Mt. Taylor,'^ New Mexico. — The western part of New Mexico owes much of its characteristic scenery to the presence of high tablelands, separated by regions of deep erosion. One of these tablelands, or mesas, is cov- ered with lava flows, and sustains a prominent volcanic pile named Mt. Taylor. The mountain has an eleva- tion of 11,390 feet above the sea. The mesa from which it rises is forty-seven miles long from northeast to south- * G. P. Scrope, " The Geology and Extinct Volcanoes of Central France," London, 1858, PL 3, 5. " The most readily available source of information concerning Mt. Taylor and the adjacent region, is " Mt. Taylor and the Zuni Plateau," by C. E. Button, in the 6th Annual Report of the U. S. Geological Sur- vey, 1884-85, pp. 105-198. 3 •HMMM w 194 VOLCANflES OF NORTH AMKUICA \. n ■v If 1 \ ' i I west, and twonty-tliroo miles Ijpoad. Its TiiMrL^iii.s are ir- rc^^nilar and deeply indented. It lias a general elevat'on ol" 8200 feet, and rises in general 2000 feet altove tlu? more thorongldy eroded (tonntry with which it is snrronndcMl. The mesa is a n^lic left hy erosion, and fnrnislies a meas- nre of a portion of the general lowering of the snrface of the adjacent conntry. that has taken plac(» owing to the action of rain, rivcsrs, and other dennding agencies. The reason why the rocks forming the hasement layer of the mesa have escaped destruction and caused it to hecome a prominent topographical feature as the adjacent region was lowered, is because of a surface layer of lava about 300 feet thick, which resisted the attack of atmo.spheric agencies nuicli more effectually than the sedimentary strata surrounding it. The Mt. Taylor mesa and neigh- boring elevated areas of the same general nature, are literally roofed with lava, which has shed off the rain, and protected the strata beneath. Mt. Taylor is composed almost entirely of lava, which rose through a single opening and built up a promi- nent cone with a large crater in the summit. The primi- tive form is now greatly altered by erosion. It stands as a ruin, in which one sees with difficulty the outlines that gave it form a;id expression during its days of maturity. The geograprer and geologist in the Mt. Taylor region, however, find less of interest in the mountain itself than in its surroundings. If we stand, says Dutton, on the eastern brink of the Mt. Taylor mesa, the view in the valley of the Puerco to the eastward is in some respects extraordinary. The edge of the mesa suddenly descends by a succession of ledges and slopes, nearly 2000 feet into the rugged and \ VoI.rANOKS Ol" NoliTII AMi:i:l< A. I'l.ATK (1. r«'.. . ... S ,.. -^ .. » .? ■■■■> »» t k*i ^ .'.-■ • *s» slS^^^«5'?> ,„;^>M,»»Ri(.; 7/"' ■'.•■! '•.•M..V- San Fninclico I'ecik. AKtiiIz I'cAk. Fid. \, Sdii Frnncisfo Mm.iiiaiii, Aiizmia, fri>in the sinitliwcst. (»'. K. Diittmi.) Fia. B. Volcanic ueck uear .Mt. Taylor, Xew Moxico. (I'hotograph by U. S. Geo- logical Survey.) mm V ^ {; VOLCANOES OF THE UNITED STATES 195 highly diversified valley-plain below. The country be- neath is a medley of low cliffs or bluffs, shoving the browns and pale yellows of the Cretaceous sandstones and shales. Out of this confused patchwork of bright colors rise several objects of remarkable aspect. They are ap- parently inaccessible eyries of black rock that rise from 800 to 1500 feet above the general level of the valley. The black piles, that by contrast of form and color make such a marked innovation in the scenery of the arid valley, are the "necks" of ancient volcanoes. To understand their history, we must restore in fancy the rocks which h" ve been carried away to form the valley, and possibly much more. Upward through the horizontally bedded rocks, openings were formed in some manner, but how is not fully known, and through these openings, lava rose to the surface and formed cones similar to the scores of cinder cones still to be seen on the Mt. Taylor mesa, and about San Francisco peak. How widely the lava spread out in sheets can only be conjectured. When the eruptions ceased, the lava slowly cooled and solidified in the chimneys through which it came. Plugs of dense rock, many times beautifully columned on account of shrinkage on cooling, were formed, which were far more resistant to erosion than the stratified beds through which they rose. Then came a long period of erosion, in the course of which many hundreds of feet of sedimentary rock, and all the lava sheets and cinder cohes which may have rested upon them, were swept away from areas which aggregate thou- sands of square miles. The necks of resistant volcanic rock in the ancient chimneys resisted waste and decay much more effectually than the softer beds of shale and sandstone with which they were surrounded, and became Jl 4 I ■', i I: i : If! 1 '« i J (^ f if » 196 VOLCANOES OP NORTH AMERICA prominent landmarks as the general surface was lowered. The leading outlines in this slow process of dift'erentiai erosion are simple, well understood, and similar to what has occurred over wide regions of the earth's surface ; but the results produced are unusually striking, owing to the bold relief of the isolated neck, the contrast of their sombre precipices with the brightly colored desert-valley alx)ut them, and the general absence of vegetation. The time required for the unearthing of the formerly buried buttes is vast, as measured in years. The date at which the ancient volcanoes were active is placed by geologists in the Tertiary period of the earth's history. A view of one of the volcanic necks de^crib* r" above is given on Plate 6, Fig. B, and will serve to show the gen- eral features of scores of similar isolated piles, more or less completely buried by the products of their own dis- integration and decay, that add variety and interest to the desolate region about Mt. Taylor. The completeness of the evidence by which the history just outlined is sustained, is shown by the fact that the volcanic necks most remote from the edge of the mesa have been completely exhumed and disengaged from the stratified beds that formerly surrounded them, while t'i )se nearer the mesa still have large remnants of the end . i» :^ strata around their bases and mounting far up their side ■, Nearer still to the border of the mesa, the amount and height of the enclosing beds increase, so that only the summits of the necks protrude. In the wall of the mesa itself, there are instances in which the volcanoes have been cut in two and one-half removed, so as to expose not only the summit of the neck of hardened lava, but a section of the cinder cone that was built above it. The <^A VOLCANOES OF THE UNITED STATES 197 one or two hundred cinder cones on the Mt. Taylor inesa ilkistrate the character of the surface which has been re- moved in tlie valley of the Puerco, in order to reveal the volcanic necks. The volcanic cones on the surface of the mesa are in various stages of decay, but some of them still retain their craters. Two of them are between 800 and 1000 feet high, and four or five others are only a little smaller. The distribution of these vents upon the mesa is very irregular. In some places they are tliickly clustered together ; in others they are separated by inter- vals of three or four miles. Much detailed information concerning the volcanic necks in the region about Mt. Taylor is given by But- ton in the attractive report from which the above descrip- tions are taken, and the student who has become interested in their history should consult the volume to which refer- ence has been made. In the valley of Rio San Jose, to the south and west of the Mt. Taylor plateau, there are lava flows with ex- tremely rugged surfaces, some of which are so recent that time has made no appreciable impression on them. These lava flows are to be seen from the trains on the Atlantic and Pacific railroad, near Laguna, and farther w^estward from McCarty to Blue Water. Portions of this route furnish typical examples of what the Mexicans term malpais, that is, the rough surfaces of lava that have been broken and the blocks piled together in confused heaps as the still liquid portion below continued to flow. The glossy black and exceedingly rugged surfaces of some of the lava coulees along the San Jos^ are of this type. In other places the corrugated surfaces of slowly moving sheets which cooled without being broken into blocks, ' ilri if"' Iff V It \ Hi, , ('. i ^1 furnish unmistakable evidence of the former liquid con- dition of the rock. Button discovered that the vent from which came the lava in the valley of Rio San Jose, is a low crater named Tintoro (the inkstand) some six miles north of Blue Water. Ice Spring Craters, Utah. — About 125 miles south of Salt Lake City and well out in the desert-valley to the west of the bold Wasatch Mountains, there are several craters which derive special interest from their associa- tion with the history of an ancient lake which once flo(jded many of the now arid valleys of Utah. The old lake referred to, named Lake Bonneville,' was in exist- ence during the Pleistocene period of geological history; the time that witnessed various advances and retreats of glacial ice over the northern portions of North America. Some of the volcanoes in the valleys of Utah are of more ancient date than the first rise of Lake Bonneville ; at least one of them had a period of activity during the time the lake basin was flooded, and several small examples, which form a compact group known as the Ice Spring craters, have come into existence since the water of the old lake disappeared. The Ice Spring craters (Plate 7) are situated on a broad featureless plain composed of the sediments of Lake Bonne- ville, known as the Sevier Desert, and are ten miles north- west of the town of Fillmore. At the locality mentioned, there are three small craters of scoria and lapilli, which are fresh in appearance and ^ A report on Lake Bonneville by G. K. Gilbert, forms Monograph, Vol. I of the U. S. Geological Survey. The craters mentioned are described on pp. 319-339 of this report. ^4 VOLCANOES OF THE UNITED STATES 199 nearly perfect in form. Closely associated with these and partially concealed by them, are fragments of at least nine other craters of similar character. About this group of volcanic vents there are coulees of basaltic lava which flowed from them at various times and cover an area of 12.5 square miles. A bird's-eye view of the three well-preserved craters and a fragment of a much larger one named the Crescent, as well as of the lava field to the eastward of the group, is shown in Plate 7. This view here reproduced from Gilbert's monograph, was constructed from sketches, with the aid of an accurate plane-table map, and will serve bet- ter than a written description to convey an idea of the leading features of the central portion of the Ice Spring craters. The Crescent, as just stated, is only a fragment of the crater wall of a volcano which has been more than half destroyed by explosions. In some respects it is to be compared to the rim of ancient date that partially sur- rounds Vesuvius, and known as Mt. Somma. The Crescent rises 250 feet above its eastern base, and when complete must have had a diameter of about 2200 feet. The central crater shown in the illustration, named the Miter, is probably the most recent of the group, as no other crater overlaps it. It rises 250 feet above its west base and 275 feet above the bottom of the pit it encloses. Its rim is nearly circular, and has a diameter of 950 feet. After it had reached approximately its present size, lava rose within it and, breaking through its north side, flowed away as a well-defined stream, which expanded on the adja- cent plain. This lava eruption was followed by one of explosive violence, during which the break in the crater II' if y* 200 VOLCANOES OF NORTH AMERICA /I'lj Vi' ' •l^'i, ) lAiW i t',. 1 'I 11 rim was repaired by the deposition of scoriaceous lapilli. The lava again rose in the crater, and again broke tlirough its wall, this time discharging westward, leaving a breach the bottom of which is seventy-five feet higher than the crater's bottom. Between the Miter and the Crescent is a low cinder cone, resembling the Miter in shape, but only 400 feet in diameter, named Terrace crater, which is well within the area formerly embraced by the Crescent. The v/alls of Terrace crater, as described by Gilbert, are for the most part low and characterized by a gentle outward slope. At their culminating point they are scoriaceous, but elsewhere they are of relatively com- pact lava, with a rude stratification, as though formed by the addition of successive sheets. Its formation was evidently attended by very little explosive action, and there is some ground for believing that its cavity was produced by the fusion of scoriaceous matter, the product of some earlier eruption. Its outline is irregular, with an extreme length of 1100 feet and a width of 700 feet. At one stage in its history it was occupied by a molten lake about fourteen acres in extent, and the partial con- gelation of the surface of this lake left a terrace at one margin. The subsequent history of the crater includes the formation of four narrow terraces at lower levels. The first lowering of the molten lake appears to have been accomplished by the breaking of the crater wall at the south, and a consequent outflow. The subsequent lowerings were caused by the retreat of the lava down the conduit by which it had originally entered the crater from beneath. This conduit remains open and can be explored for twenty-five feet, when progress is stopped (4 i .J, I /f 'A ■r. ■I, ■r. » ri i ■ ■'% I i wml^n9ml^^•'^'•^^w^r^!^ VOLCANOES OF THE I'NITED STATES 201 by water. It is a circular tube twelve feet in diameter, and inclined ten or fifteen degrees from the vertical. Tlie stony, arrested drops still pendent from its sides testify by their small diameter to the high fluidity of the lava. The depth of the crater below its general rim is 260 feet, below the sill of its last outflow 220 feet, and below the scoriaceous crag that overlooks it on one side 350 feet. The streams of basalt flowing from the Ice Spring craters — still quoting Gilbert — have formed two con- fluent fields, the first extending three and one-half miles northward, with a general breadth of two miles, the second three and one-quarter miles westward, with a general breadth of one and one-half miles. Their area is approximately twelve and one-half square miles. Their marginal depth will average about thirty feet, and their mean depth is estimated at fifty feet. The volume of the ejected material is approximately one-eighth of a cubic mile. The lava is black or dark gray basalt, with exceedingly rough surfaces, due to the breaking of the crust as the still plastic portion beneath continued to flow. In places the surface blocks are piled in confused wave-like ridges, whose crests are twenty or thirty feet above their troughs. One curious feature of the lava streams that flowed from the Ice Spring craters and fed the surrounding coulee, is that near the craters they are depressed fifteen or twenty feet below the adjacent surface. The appear- ance is as if the streams of molten rock had eroded channels for themselves. Yet, as stated by Gilbert, the adjacent surfaces resemble very closely the surfaces of the streams. " The explanation appears to be that each 1] '1 f' I lii i jf -m^*>m I I . ) 202 VOLCANOES OF NORTH AMEllirA ')! 1 1 1 > . ■11 < I , I : ) M ( \ H I of these outpourings varied in volume, now swelling, now sinking. When most copious, it spread beyond its channel like an ac^ueous stream and deposited, not its sediment, but its crust. The walla of the channels dis- play a conformatory stratification." Tabernacle Crater and Lava Field, Utah. — Four miles south of the Ice Spring craters, there is another volcano more recent than the withdrawal of the water of Lake Bonneville, and named Tabernacle crater in reference to its resemblance, when seen from a distance of a mile or two, to the great assembly building in Salt Lake City, known as the Tabernacle. Tabernacle crater is composed of the same varieties of basalt as the Ice Spring crater, and has two crater rims, one within the other. Surrounding the crater is a nearly circular lava field about three miles in diameter, with an area of approximately seven square miles. The point of issue is not central, but lies near the southeast margin of the lava coulee. The outer rim of the crater, one-third of which has been removed, has a diameter of 2200 feet and on the highest side rises 120 feet above the surrounding lava fields. The inner rim, composed of scoriaceous material, is complete in general form, but is rough and abounds in pinnacles. The chief phases in the history of Tabernacle crater, as determined by Gilbert,^ are as follows : When Lake Bonneville stood at a comparatively low level, known as the Provo stage, it has a depth of from fifty to seventy- five feet above the valley bottom where the crater now ^"Lake Bonneville," U. S. Geological Survey, Monograph, Vol. I, pp. 329- 332. :i VOLCANOES OF THE I'NITED .STATES 203 stands, and was held at a constant level for many centu- ries. An explosive eru})ti()n occurred beneath the lake, of such violence that the material hhnvn out was deposited most abundantly at a distance of more than a thousand feet from the point of discharge. The rim built up by this explosive eruption eventually rose above the surface of the lake and shut out its waters. The eruption then became less violent, and the material discharged changed, becoming pasty. (^uiet eruptions followed, developing a low black iisland which had a line traced about it by the waves before the lake was finally lowered by evaporation. The declining phase of the eruption was again explosive. The lava field about Tabernacle crater terminates in most directions in a steep cliff, showing that the lava flowed sluggishly, and was of such consistency as to form a deep stream instead of spreading widely and ending in a thin edge, as is the habit of very liquid lavas. The surface is rugged, on account of the breaking of the crust by the motion of the still liquid portion beneath. The sinking of the blocks formed by the breaking of the crust into the plastic lava, may have increased the fric- tion of flow, and thus caused the flood to advance with a precipitous terminus. The height of the outer escarp- ment is in places sixty-five feet. Among the minor points oi interest to the student of volcanic phenomena at the Ice Spring and Tabernacle cra- ters, is the presence of lapilli w idely scattered on the lava flow, showing the violence with which the fragments were thrown out, although there is an absence of evidence showing excessive energy. Near the craters much of the scoria was ejected in a pasty condition and came to rest n ^v n h \ t. ''1^ _»,.-....„; Ov.swiiSfl li ' V' 204 VOLCANOKH OF NOUTII AMKUICA . ( , » ! > |!|i ■If wliilu Htill plastic. Some of the bombs tiro possibly a mile from the crater from which they started on their aerial journey, but struck the ground while still plastic, and were flattened so as to form cakes, in some instances between two and three feet in diameter; on the under side they preserve impressions of the rough surfaces on which they fell. Well-formed spherical bombs, charac- teristic of many volcanic regions, which cool during their passage through the air and sometimes exhibit a si)iral twist due to rotation while still plastic, were not noticed. The surfaces of some of the lava Hows, particularly in the neighborhood of the Miter, are exceedingly rugged, on account, as already mentioned, of the breaking of the crust formed on the surface, while the still plastic portion below continued to flow. The rough surfaces thus pro- duced are of the same character as the fields of the Hawaiian islands. Tn some instances about the Ice Spring craters, especially, the under surface of the angu- lar blocks formed by the breaking of the crust are grooved and striated in a striking manner, and show the effect of the friction of the moving undercurrent while the crust was yet plastic at a depth of eight or ten inches below the exposed surface. The interstices of the lava in the coulee about Taber- nacle crater are in some places filled Avith fine, yellowish dust, wdiich has gained access to steam cavities, through openings too small to be distinguished by the eye. While the Ice Spring and Tabernacle craters are young as compared with the fall of the water of Lake Bonne- ville below the lowest notch in the rim of the basin that confined it, yet their absolute age in years cannot be determined. The lavas are fresh in appearance, and no- VOLCANOES OF THE UNITED STATES 205 a ir I ,'S 'P fM 1 where have yicjldoJ to tlio action of the atmosphere so as to form a soil. It is to be reiuem))ure(l, however, that under the dry eiimate of Utah, such a change is exces- sively slow, and tlie fresh appearance of the lava is not an argument in lavor of very recent origin. In the same valley with the volcanoes just described, there is another of older date, named Pavant butte, about which the waters of Lake Doinieville left conspicu- ous markings. This volcanic pile is formed of lapilli, and furnishes evidence that an eruption took place when the lake was at its highest stage, and beneath a body of water 350 feet deep. The resulting cone was built not only to the surface of the water, but 450 feet higher. Eruption ceased with the fall of the water and has not since been renamed. A detailed and instructive account of this volcano may be found in the report on Lake Bonne- ville, already referred to. Craters near Ragtown, Nevada. — The craters in Utah, just described, derive much of their interest, as has been seen, from their association with the history of Lake Bonne- ville. In Nevada there was another great lake in Pleisto- cene times, contemporary with the one in Utah, which is known as Lake Lahontan. The Nevada lake also had volcanic phenomena associated with its history. One of the broadest portions of Lake Lahontan occu- pied what is now the Carson desert, Nevada. On the inner slopes of the mountains surrounding and nearly enclosing this basin, there are shore lines which show that at one time it was flooded to the depth of 500 feet above the stratified clays now forming its floor. In the western part of the desert, about two miles from a little settlement named Ragtown, and twenty-two miles southeast of Wadsworth, i i lU ■ ^ '1 ! 1' '!;.: ,)i 1 I Mil I' I f - I I ('ji' J m I In M ! 20G VOLCANOES OF NORTH AMERICA a town oil the Central Pacific railroad, there are two circu- lar depressions occupied by strongly alkaline water, which are termed the Ragtown ponds, or Soda lakes. These lakes occupy volcanic craters the rims of which rise above the surface of the surrounding sage-brusL-covered desert, while their bottoms are depressed below that hori- zon. The rim of the larger crater, at its highest point, is 80 feet above the desert and 165 feet above the surface of the water within. The water has a maximum depth of 147 feet, making the total depth of the crater 312 feet. Its bottom is 232 feet below the desert's surface. The least diameter of the crater at the water's surface is 3168 feet, and its greatest diameter 4224 feet. The area of the lake is 268.5 acres. The diameter of the crater, measured from opposite points on the summit of its rim, might be vari- ously determined, owing to the lack of a well-defined crest at all places, but in general is about one mile. The smaller lake is much inferior to its companion in all di- mensions. Its diameter from points on opposite sides of its low and not well-defined rim, is about one-half mile, and its depth to the shallow pond within, approximately seventy feet. The measurements just given show that the larger crater is by no ineans insignificant. The proof that it was produced by volcanic explosions, and also its place in the history of Lake Lahontan, is shown by the fol- lowing evidence. The general form of the crater, that is, a depression surrounded by a raised rim, is such as frequently results from the blowing out of projectiles when volcanoes of the explosive type are in action. Sections of the wall of the crater show that it is com- posed of lapilli and volcanic dust, together with numerous T-^f-rf.rTrtrwi'rc M VOLCANOES OP THE UNITED STATES 20i ' I U scoriaceous fragments of basalt. The basaltic masses are of all sizes up to two feet in diameter, and occur at all heights in the crater's walls from base to summit, and on the adjacent surface of the desert. Frequently, in the case of freshly exposed basaltic masses in the crater walls, the strata of fine, loose material on which they rest are beat down in the manner that would be expected had the " bombs ' been thrown into the air and fallen to their present position from a height of several hundred feet. The layers of lapilli forming the crater's rim are fre- quently inclined both in the direction of its outer and inner slopes, and are also frequently interrupted or uncon- formable, portions of the deposit having been removed, as is common in the case of craters that have been par- tially destroyed by the violence of the explosions from within, and subsequently rebuilt. Interstratified with the layers of volcanic origin are beds of lacustral clay and deposits of calcareous tufa. The tufa is identical in origin, so far as one can judge, with extensive sheets of the same character occurring at numerous localities throughout the Lahontan basin, and determined to have been precipitated from the waters of the former lake. The evidence is clear that the volcanoes whose craters are now occupied by the Soda lakes, were in activity during the existence of Lake Lahontan, and also that the last eruption occurred since the lake waters fell below the level of the Carson desert. The outer slopes of the crater walls are not marked by terraces, as would have been the case had such piles of loose, incoherent material been 3xpo::ed to wave action. The volcanoes were of the explosive type and threw out only fragmental material. No lava streams are associated with them. 'I n '1 !1 ■ i .51 Si hi : I 1 I ' tMvn w^'lli:)^w\ '■ !■■ I ' .^-.Uiy."!" I'y.j^JW 208 VOLCANOES OF NORTH AMERICA i ' ,\ i t Mi The Soda lakes are the basis of a considerable soda industry and are of interest also on account of the crus- taceans and insects that live in their waters. In the larger lake, crystals of a pure white soda mineral named gatjlussite, are forming. The composition of the waters of these lakes and other facts concerning their history are given in the books mentioned in the following foot-note.^ Volcanoes of Mono Valley, California. — Mono valley is situated at the eastern base of the Sierra Nevada, in about the centre of the eastern border of California, but extends across the interstate boundary into Nevada. In the lowest part of the valley and reaching the base of the steep eastern slope of the Sierra Nevada lies Mono Lake, a body of intensely alkaline water. The eastern portion of Mono valley partakes of the desert-like character of the great interioi arid region of which it is a part ; but its western and southwestern por- tion is well watered by streams which have their sources in the forest-covered Sierra Nevada. Like many other enclosed basins between the Sierra Nevada and Rocky Mountains, Mono valley has an instructive history of climate fluctuations, in the form of terraces, lacustral deposits, glacial moraines, etc., written on its inner slopes, but at present we must pass this by. In the centre of the lake at the present time there are two islands, named Paoha and Negit islands, besides sev- eral rocky crags. We will begin our studies of the instruc- tive volcanic phenomena of Mono valley by examining these islands. Let the reader in fancy take a seat beside me in 1 Arnold Hague and S. F. Emmons, U. S. Geological Survey of the I orti- eth Parallel, Vol. II, 1877, pp. 744-750. Clarence King, U. S. Geological Sur- vey of the Fortieth Parallel, Vol. I, 1878, pp. 510-514. I. C. Russell, " Lake Lahontan," U. S. Geological Survey, Monograph, Vol. XI, 1885, pp. 76-PO. .1\ VOLCANOES OF THE UNITED STATES 209 i a small boat, with a single Indian from the encampment on the shore to use the paddle, and I will endeavor to point out some of th ^ more instructive features that pre- sent themselves as we glide over the placid surface of the lake, on our way to the islands. The water over which we pass gives the fingers a slip- pery feeling ; if we taste it we find that it is intensely alkaline and ])itter. As we look down into the water we see that it is clear and limpid^ but the view is usually obstructed by countless numbers of brine shrimps {Artc- mia) and the larvce of flies. The lavae are thrown ashore by the waves in windrows that are frequently a foot or more deep. The lava cases on drying are detached from the dried worms within and may be easily separated On the sloping sandy shore near an encampment, you may see a number of Indian women with large conical baskets on their backs, and a second shallow paddle- shaped basket in their hands. With the flat basket they throw the dried larvae in the air and allow the w^ind to carry away the chaff-like cases. The desiccated worms are then transferred to the baskets on their backs, to be used as food. On the borders of the valley we can see the horizontal lines at various heights that mark the level of the w^ater in former times. The highest of these lines, wdiich is drawn about the steep faces of outstanding bluffs and continued into the lateral valleys between, is 675 feet above the present lake surface, but is not now perfectly horizontal. A movement in the rocks has taken place since the lake was at its highest stage. The differences in elevation at various points in the old beach line, how- ever, are not over fifteen or tw^ntv feet. '■A lil •J |-' if 'I. ¥ i» U fv II i»l .'? ,i Hill r i' it 210 VOLCANOES OF NOUTH AMERICA The scene that invites the attention of tlie traveller in Mono valley to the exclusion, for a time at least, of all other features, is the range of niagnilicent mountains that limits the view to the southwest. The surface of the lake is G380 feet above the sea. The highest of the serrate peaks, Mt. Dana, rising precipitously from its border, reaches G612 feet above us, and is 12,992 feet above the sea. Twelve miles south of Mt. Dana and also on the rim of the basin surrounding Mono Lake, stands Mt. Lyell, 13,042 feet in height, amid a group of white cathe- dral-like spires that are but little inferior to it in eleva- tion. On the northern sides of several of the '.igher peaks in view there are small glaciers, which contribute the water formed by their melting to the swift streams supplying Mono Lake. In the deep gorges excavated in the sides of the mountains we can distinguish the rounded contours of the valleys due to the broadening and smooth- ing of stream-cut valleys by ancient glaciers. When the gorges open out into the plain bordering the lake, they are conspicuous moraines, which in several instances are prolonged from the entrances of the high grade-valley, as parallel morainal embankments, more than a thousand feet high, which were deposited on the Ijorder of the ancient glaciers after escaping from the confinement of the moun- tain precipices. To the south of the lake, and separated from the rugged eastern face of the Sierra Nevada by an extension of Mono valley, rises a conspicuous range of volcanoes which fur- nish some of the most pleasing and instructive features in the diversified landscape. These volcanoes are known as the Mono craters, and will be examined after our visit to the islands which in fancy we are nearing. ^) VOLCANOES OF Till-: I'MTED STATES 211 The larger of tlie two main islands is mild in relief and alnKJst white in color, while the smaller one is rugged and nearly l)lack. These diii'erences have an intimate connec- tion with their origin and geological history. In seeking for a name hy which to designate the islands, during my exploration of Mono valley, it was suggested that their contrasts in color might he used, hut 1 preferred to record some of the poetic words in the language of the ahorigines who still inhalnt the valley. On the larger island there are hot springs and orifices through which heated vapors escape. These hot springs and fumaroles are the linger- mg remnants of V(jk'anic energy which, in times not remote, built some of the most conspicuous landmarks in the valley. It seems fitting that the words of the Pa-vi-o-osi people, who, like the volcanic energy, are fast passing away, should be attached to the scenes with which they have long been familiar. Among the legends of the aborigines there is one concerning diminutive sprites hav- ing long, waving hair, that were sonietimes seen in the vapor-wreaths escaping from the hot springs. The word Pa-o-ha, by which these elves were known, is also used to distinguish the hot springs themselves. We therefore named the larger island in memory of the children of the mist that hold their revels there on moonlit nights, Paolia Island. The island near Paoha Island, and second to it in size, has been called Negit Island, Negit being the Pa-vi-o-osi name of the blue-winged goose. On reaching Paoha Island, we find shelter for our boat in a cove on its eastern side, which we recognize at once as being a partially submerged crater of basaltic lapilli. The side of the crater facing the lake has been broken if if V 212 VOLCANOES OF NORTH AMEllICA i ( ' / ' , II I. :■ h'' \i down, and the lake water now extends into the cavity kept open at the time the crater was formed by tiie vio- lently escaping steam. On walking over Paoha Island, we find tliat the white- ness of its surface, which we noted on approaching, is due to a thick deposit of lacustral clay and marl, together with considerable quantities of volcanic dust, which was showered down on the lake when its surface was consider- ably higher than at present and the island Avas completely submerged. On the surface of the lake beds and evi- dently dropped there since the island was left exposed by the recession of the lake, we find masses of scoriaceous basalt, which become more and more numerous as we approach an elevation on the northeast extremity of the island and only a quarter of a mile north of the cove in which we landed. Mingled with the blocks of basalt are numerous rounded and water-worn pebbles of granite and other rocks, which one familiar with the geology of the Sierra Nevada will at once recognize as being similar to the rocks there exposed and identical with the pebbles in the streams that flow from the mountains. As these peb- bles, like the blocks of volcanic rock with which they are mingled, do not occur in the lacustral sediments, so far as we can discover, it is evident that they reached their pres- ent resting-place at a recent date. Since the pebbles are not covered by lake sediments but rest on them, they must have been brought since the island eme.ged from the water. Without going over all the steps in the evi- dence by which an explanation of the presence' of the pebbles was reached, I may say that in company with the blocks of basalt and much lapilli and dust associated with them, they were blown out of a crater on the VOLCANOES OF THE UNITED STATES 213 island, and fell on the adjacent surface at a recent date. The crater from which they came forms the hill already mentioned, on the northeast point of the island. A map of this locality, including also the partially submerged crater in which we left our boat, is given below. In further explanation of the presence of the pebbles referred to, I may say that similar water-worn rocks occur on the neighboring Mono craters even to their summits. Previous to the origin of Mono Lake or dur- \. A K E Fui. 7. North end of Paolia Island, Mono Lake, Cal. (Surveyed by W. D. Johnson.) ing a period of low water in its earlier history, the streams from the mountains spread a sheet of gravel over the valley. The volcanic vents were opened through this deposit, and the violence with which steam escaped, carried the stones upwards in much the same manner that volcanic bombs are projected out of volcanic vents, and scattered them over the adjacent region. These pebbles of granite are similar, so far as their connection with the volcanoes of Mono valley is concerned, with the blocks of limestone thrown out by Vesuvuis. At Vesuvius the !l ''I , '^ I 214 VOLCAN'OKS (»K NOUTII AMEUK'A iM'i rw' volcanic conduit traverses liin' stones, portions of which are torn off by the violent uprush of steam or forced into the conduit Ijy steam explosions from its sides ; in Mono valley the volcanoes opened conduits througli a stratum of gravel and rounded boulders, some of which were carried to the surface with such violence that they were projected high in the air, and fell about the craters. Each of the bowl-shaped depressions shown in the accompanying sketch-map is a crater of recent date. They do not contain lacustral clays and are not scored with beach lines on their outer slopes. The loose inco- herent nature of liie material of which they are composed renders it evident that they could not have withstood the action of w^aves and currents for even a Ijrief period with- out having evidence of the fact inscribed upon them. They are, therefore, more recent than the last high-water stage of Mono Lake. The largest crater is from 150 to 175 feet deep. The regularity of its outlines has been broken by the formation of two smaller craters on its rim. The narrow ridge of lapilli separating the main crater from its larger parasite, forms a symmetrical curve, as it descends from one end of the broken rim of the older crater and ascends to the oppo- site extremity. The craters separated by the low wall hold lakelets of strongly alkaline water, whose surfaces are on a level with Mono Lake, from which they are supplied by percolation. The waves of the surrounding lake have carved away the base of the outoi" slope of the crater on the north and east, and made it precipitous, and will no douljt soon open breaches through it. so that the lake- lets will have open connections with the surrounding w^aters. A submerged crater a few rods from shore, .■■*-t. .■•-i.'-i,Au',.> 1. VOLCANOES OF THK LNITKI) STATES 21 r, revealed )>}' soundings, shows that one nieniljer of the group has perhaps already succumbed to the attack of the waves, or else was formed by explosions beneath the lake's surface. On the west side of the craters described above, there is a small lava flow, also shown in Fig. 7, which descends into the lake. That this lava stream was formed at a recent date is at once suggested by the fresh appearance of the black, angular blocks composing it. The lava is not covered with lacustral sediments, and is without cer- tain calcareous incrustations, which are common on simi- lar rocks in various parts of the valley below the ancient beach lines that record the former horizons of the lake's surface. The lava flow is, therefore, more recent than the latest high-water stage of the lake. It is also of more recent origin than the neighboring lapilli craters, as its surface is free from the debris showered over the island when they were formed. The lava descends into the lake without change of character, thus indicating that the sur- face of the water, at the time of its extrusion, was lower than now. The distinctions, however, between the char- acteristics of a subaerial and a subaqueous lava flow are not sufficiently well determined to allow one to decide in all cases in which manner an eruption occurred. The central portion of the small lava flow just descril)ed is lower than its sides. After the sides and surface had cooled and hardened, the still liquid interior flowed out and allowed the surface crust to subside. On looking down on the surface of the lava stream from th '^djacent elevations, another interesting fact is to be noteu. The apparent chaos of angular blocks composing it, is not in reality without some order. The larger blocks are heaped ••I 216 VOLCANOES OF NOUTH AMERICA •I , ! i I in crescont-shapc'd ridgos, which cross the stream and are convex in the direction of flow. Several of these curved ridges may be easily distinguished, wiiich are concentric, one with another, and reseuible in a generjil way the curved terminal moraines to l)e seen in many formerly glaciated valleys. The wave-like appearance of the sur- face of the lava How is due to pulsations in the stream of molten rock, caused by the clogging of the current by the blocks of hardened lava floating on its surface. The rock forming the lava fl(nv just descriljed has been studied by Professor J. P. Iddings, and found to be essen- tially a hypersthene andesite, although its microscopic structure is somewhat indefinite. It is on the dividing line between andesite and basalt, but apparently the weight of evidence places it in the former. It is a black, fine-grained, couipact rock, breaking with a conchoidal fracture, and to the field geologist has all the appearance of basalt, but is free from olivine. This outwelling of lava came from near the base of the lapilli crater described above. It is the latest extruded material on Paoha Island, and probably the last igneous discharge in Mono valley. Negit Island is composed of a crater, and of a coulee of lava which extends a third of a mile southward from its base. The recent origin of the island is attested by the absence of lacustral deposits, but a thin coating of cal- careous tufa extending twenty feet above the 1883 level of the lake, shows that the coulee is of somewhat older date than the similar lava streams on Paoha Island. The rocks composing Negit Island are even more basaltic in appearance than those of its neighbor, but are classed by Iddings as hypersthene andesite. The crater is unlike any '* VOLCANUKS OF NOUTir AMKRICA. PI.ATK 8. ^V, "■.^f^A:v:: 'anumCritisr ;, '. ■;"■■■,.'■■ ■'.'■'■■■"''*'*:'/"''•'•■•' ■''>■>•'' / ■'■■. '■•'•-■.■ •: "'.ji' •;';■.',':'■■.•; ; ■:' :'■.'.■■. .:■,•,;■• ''^.'■'. ''.VV;. >.- I« •;••• .•■\i' • • ■■. ^>. ■■ ■, (.- •'.■ ■■■>■■■■■- ^^'t •• ''tV.^! '-'V . t^'-TSKflff^ ,'' •■ J^< .■■' "/J olMWBuH y-^^^S,... ■ ' ««l-'':>-'V.>;/./' .... •;•,■ ■ ' "!*:;■•■"■ ■ • ^V/ ::^ u^ 2oi ■■•.■.■..■•.■■. '. ■::rm-K: :':S':- > ^>i^^:i^:v,'5?p .;;:,\;;^; v^^l.^ Vy--,. ,.>:v. MONO CRATERS 3 3 ^ i ^ 1 J. ■ 'f Ml 4 mile;. Elevations al)ove Lake Mono srivpn in feet. 'fl ti I -=_ ," •— a: •gy— * i fiw ■ ■ iBgysiiiraMU'a;^^ ^* ( » ff If. I 1 VOLCANOKM (»K TIIK I'NITED 8TATKM •-'17 other in Monu valley. juhI is not a lii')illi cone, but is com- posed of scoria, which was ejected in large aenii-plastic masses. No dust or lapilli is scattered over the rugged surface of the black lava. The crags and isolated rocks in Mono Lake to the north of the two principal islands, are fragments left by erosion of ancient mica andesite (also a volcanic rock) similar to the l)asement rock beneath the lacustral marls and recent hipilli dei)osits of Paoha Island. From the Negit Island southward to the end of the Mono (;raters, when they come down nearly to the lake shore, is but a little over four miles. When the wind is fair, this distance is quickly sailed. On approaching the shore, we find it fringed with a broad belt of white frotii. The alkaline waters are easily churned into foam, which after a gale is frequently two or three feet deep, and is blown ashore in cotton-like masses, that are rolled along by the wind, and even reach the desert vegetation fring- ing the desolate area near the lake shore. Let us continue our excursion by ascending the Mono craters. The Mono Craters. — The grouping of these craters and the positions of the coulees of lava that have flowed from them are shown on the map forming Plate 8. They form a slightly crescent-shaped range of mountains, ex- tending south from Mono Lake to a distance of about ten miles. More than twenty complete or partially Ijuried craters can be recognized. Others are no doubt concealed beneath the products of the more recent eruptions. The highest, and, judging from their eroded condition, the oldest, of the well-defined cones in the range are in its central part. The four higher summits rise in order from north to south, 2455, 2749, 2620, and 2595 feet, respec- I t ti J ! I I /» ! I, ,r I ! j": i :! I ! Ill !!'! ,,i SI \'J I I 218 VOLCVXOES OF NORTH AMEltlCA lively, above the surface of Mono Lake, which, as previ- ously stated, is C380 feet above the sea. The Mono craters are composed largely of clastic ma- terial, of which a light gray lapilli forms the greater part. Tliere are also several coulees of lava which flowed out in a molten condition and consist, in large part, of a denh,. black glass termed ohsidicm. These two methods of ex- trusion have produced striking contrasts in the form and color of various portions of the range. The accumulations of lapilli have a light gray tint, and smooth, even contours. All of the cones are composed, to a large extent, of this material and are especially pleas- ing and beautiful to the eye on account of their graceful carves and soft, harmonious tints. In marked contrast with the lapilli deposits are thick sheets of black ob- sidian of recent date, which have flowed in various direc- tions and usually from nea: the crest of the range. The surfaces of these overflows are angular and rugged to the last degree. As shown on the accompanying map, one of these outpourings of volcanic glass occurs near the south- ern end of the range of craters, and another of less size near its northern end. Owing to the highly viscous condition of the lava of these coulees at the time of its extrusion, it formed thick sheets, which terminate in precipices betv.een 200 and 300 feet high. The slow-roovinsj: lava congealed and came to rest on slopes so steep that it seems almost a miracle that they should have remained in such positions. The contrast presented by the lapilli deposits and coulees, which consist of the same magma cooled under different conditions, is most striking. The fragments composing the former are open in texture, vesicular, VOLCANOES OF THE UNITED STATES •JIO light-colored, aiul funii siiiootli, oven slopes with incli- nations of about 30"; the obsidian is a dense, black glass without cavities or steam l)lebs, but al)ounds in stony inclusions, and frequently has its surface dusted over with lapilli that fell upon it while it was still somewhat plastic. The Mono craters are markedly different from any other volcanoes in the United States now known. The rock composing them is a rhyolite, and is highly acidic. It presents marked contrasts to the basic material com- posing the great majority of recent volcanic rocks the world over. The volcanic history of ^Nlono valley will repay more careful study than it has thus far received, for the reason that the phenomena there so^ well dis- played are, in a great measure, unique. As previously stated, the lofty central cones in the Mono craters are considerably eroded and have lost their craters. Their summits are blunted and the removal of lapilli has exposed crags of rough lava. The volcanic energy early in the history of the range, evidently found an avenue of escape where the central cones now stand ; and when the conduits of these craters becan"3 clogged, newer craters Avere formed botli to the north and south along the same line or belt of fracture. In general, tlie craters appear fresher and fresher the more remote they are from the centre of the range. A good illustration is thus furnished of the well-known fact that volcanoes are frequently located on fissures and that when one conduit becomes closed others are opened along the same line of fracture. More could be said in thi;r connection in refer- ence to the volcanoes of the Mono region, since the Mono craters, although a unit in themselves and forming an p-« rt 220 VOLCANOES OF NORTH AMERICA ;». i .. i ; * isolated and well-defined group, are in fact a portion of a much more extended series of recent eruptions, which follow the general course of the great b(;lt of branching faults which determines the eastern face of the Sierra Nevada. Tlie craters on the island in Mono Lake are on this belt of disturbance. Northwest of the lake there are other volcanoes. South of the Mcjno crater the same belt of recent cones is continued and is marked by recent craters of both acidic and basic lava, for at least a score of miles. There are some exceptions to the statement that the most recent eruptions occurred at the ends of the Mono craters, since two or three of the smaller craters irdr the centre of the range and high up on the flanks of the large central cones, are fresh in appearance and possibly as recent as the vents at the extremities of the series. The craters which still preserve their shapes and show but slight evidence of having been modified by erosion may, for convenience of description, be divided into two groups, although in reality there is no true dividing line between them. In the case of the craters forming the first of these groups, the lapilli fell on all sides of the place of extrusion i;nd built up symmetrical rings, enclos- ing conical basins. Some of these are depressed bowls with scarcely a vestige of a raised rim about them ; while others are well-defined cones rising steeply from the sur- rounding surface, and have deep conical depressions in their summits. Tlie craters of the second group are similar to those just mentioned, except that they gave egress to molten lava. The craters that were points of eruption for both lapilli and lava may again be divided into two groups: (1) Those VOLCANOES OF THP] UNITED STATES 221 in which the lava did not escape from the IjowLs formed by the violent extrusion of fragmental material, and (2) those from which the lava overflowed and formed more or less extensive coulees. As may be seen at a glance, these variations depend simply on differences in the intensity of the volcanic activity. The first eruption in each in- stance was a violent ejection of connninuted and usually scoriaceous, but at times compact and glassy rhyolite. In the craters formed entirely of lapilli, the eruptions ended at this point. In other instances, an escape of viscid lava took place through the same conduit from which the lapilli came. In some cases when an upwell- ing of lava occurred, it barely entered the bottom of the bowl of lapilli before becoming congealed. The eruption then ceased, so far as that individual vent was concerned. At other times, the thick, viscid lava was forced up in the centre of the crater until it stood higlier than the encir- cling rim of lapilli but did not expand laterally. In in- stances of this nature there is a deep, moat-like depression between the rough and angular protrusion of lava and the smooth inner slope of the encircling crater, in which one may walk entirely around the ce .tral tower-like mass. The type of this variety of eruption is furnished by the crater shown in the following illustration, which stands near the shore of Mono Lake and has been named Panum crater. Where the upwelling of lava was larger in amount, it broke through the encircling rim of lapilli and flowed away as a stream, or coulee, of lava, which, on account of its viscous nature, — characteristic of all the lava flows from the Mono crater, — ended in a steep border composed of angular blocks. The surfaces of the streams, ^ J I, ' Vi f t l( I' ' 11 |1 .! ■ * I J • 1 1 \ m\ ' \ \ ■ I I ■ H , ooo VOLCANOES OF NORTH AMERICA in all cases, also, are of this same character ; their broken and angular condition being due to the rapid cooling uf the lava at the surface, while the interior was still i)lastic and moving. Tlie surfaces of the streams are sometimes highly vesicular, and so filled witli steam bubbles that the rock is a true pumice ; at other times, especially in the case of the larger streams, the blocks are of dense black obsidian. To walk on the chaos of angular fragments, in the latter instance, is like crossing a field covered deeply with huge blocks of broken glass. Fio. 8. Panum Crater : Lake Mono and Paoha Island in the distance. (From a photograph.) Some of the variations presented by the Mono crater, due to differences in the relative amounts of lapilli, and of lava extruded, are indicated in the following series of cross-sections of a few of the craters. These are sketch sections and are not drawn to a uniform scale. In the diagram, a is a depression in a field of lapilli, and has a level floor of the same material ; 6 is a lapilli crater, also floored with material of the same character as that forming the rim ; c is a crater similar to h, except that a few crags of scoriaceous rhyolite in its bottom mark mf VOLCANOES OF THE UNITED STATES '223 the position of the summit of a phig of hiirdened lava, that exists beneath ; in the crater marked d, the hiva has risen so as to be higher tlian the wall of lapilli encircling it; this is intended to show the condition existing in Pannni crater, illustrated also in Plate 8. A oontinnation of the sei'ies might be made by adding cross-sections of craters in which the lava has broken through a rim of lapilli and advanced on the adjacent surface. Figu?'e e illustrates still another variety of crater which is represented by at least one example, the steep-sided depression in this in- stance is due to the subsidence or retreat of the lava which — ^N. y* ti j; if) d c Fi;h tlic liardeiied lava, partially fdling its ancient chainiel, leaving portions of the lava rock as a terrace on the border of the canyon, but has excavated a narrow gorge more than a hundred feet deep into the rocks Ijcueath. The lava streams mentioned above show no (evidence of having been glaciated, but retain their original rough- ness of surface. They are considered as being of more recent date than the time when the glaciers llcjwinu' from the summit of the peak reached the plain below. That is, the most recent lavas were poured out subscijuently to the Glacial epoch. As shown })y J. S. Diller, the post-glacial coulees, how- ever, form only a thin cover on the sloix's of Mt. Shasta. The great mass of the lava composing the mountain was extruded previous to the last great climatic change which enabled the glaciers starting at its summit to How to the plain below. Although the great body of the mountain is made up of coulees of lava, it contains a large propor- tion of fragmental material, and must be considered as a mixed or compound cone. As already stated, Mt. Shasta is a doul)le cone, — Mt. Shasta proi)er, and Shastiua. These two sunuuits are so closely united that tlu!y make but one cone Ijelow an altitude of 10,000 feet. Besides the two jn-incipal vents there are remnants of more than a score of subsidiary ones which contributed to the upbuilding of the moun- tain. Many other secondary points of eruption are no doubt conc(,'aled beneath the u;reat coulees now formins the outer sheathing of the great cone. I r 228 VOIX'ANOKS OK NOllTII AMKUICA r- I I A. I!' . Il^ i Tilt' LJirt'ful studies of Mi. Sli.ista contliictcd \>y Dillur liavu sliuwii tliat it is c()in[)<)scMl of in.iiiy variclii's of volcanic rock. Its chief const it lU'iits, however, arc amlL'- sitc, rhyolitc, and basalt. The iiKtst ahuiidant rock is hypersthene aiidesite — a lava containing little or nu hornhlcnde. hut much h}[)ersthene. It ranges in color from light and dark gray, often reddish, to l)lack. lia- salt occurs only on the lower slopes of the mountain, but forms nearly all of the numerous cinder cones on the adjacent plain. One of the interesting features of the lower slope of the mountain is Pluto's cave, formed by the flowing out of the central portion of a lava stream after its surface had cooled and hardened. This cave where best devel- oped is from sixty to eighty feet in height, from twenty to seventy broad, and has been followed f(jr nearly a mile without finding its extremity. The floor of the cavern is nearly flat and covered with debris that has fallen from the sides and roof. The roof above it is from ten to seventy-five feet thick, and the lava of which it is com- posed is full of cavities formed by the expansion of steam while the magma was still plastic. Many other interesting and instructive facts concerning Mt. Shasta may be found in the graphic and most attrac- tive monograph from which this account has been largely compiled.' Cinder Cone, near Lassen's Peak, California. — The Las- sen's peak district is situated in northern California be- tween the Sacramento valley and the broad area of 1 J. S. Diller, " Mount Shasta, a Typical Volcano," National Geographic Monographs (published under the auspices of the National Geographic So- ciety, by the .\nierican Book Co.), Vol. I, 1895, pp. 237-2(58. < u < ! 1 (I m I' A i «ij, |i[ 1^ ' (■; 'i w 4 : ■ VOLCANOES OF THE UNITED STATES 229 interior drainage to the east, known as the Great Basin. The volcanic peak from wliich the district derives its name rises 10,437 feet aljove the sea, and is considered as marking tlie soiitliern terminus of the Cascade Mountains. The Lassen's peak district is crossed from northwest to southeast l)y a belt of volcanic cones, abort lifty miles long and twenty-five miles wide. The great peaks which form the dominant features of this ridge are Butte moun- tain, Lass^ij's peak, Crater peak, and Burney butte. Be- sides these there are many smaller conical hills, which are also of volcanic oriuin. By far the most abundant rocks in the Lassen's peak district are those that have cooled from a fused condition and are both intrusive and extrusive. They exliil)it great variety, oi account of differences in structure and in min- eralogical and chemical composition, and range from basalts having as low as forty-nine per cent of silica, through andesites and dacites to rhyolites, some of which contain over seventy-four per cent of silica. The latest volcanic eruption in the district briefly described above, occurred at what is known as the Cinder cone, ten miles northeast of Lassen's peak. A general view of this locality, taken from a neighboring summit to the northward, is shown on Plate 10, Fig. A. A map of the same locality is presented on Plate 11. As shown in these illustrations, the most striking topographic feature of the region is a conspicuous and very characteristic cin- der cone, from the base of which a rugged and exceedimrlv fresh-looking lava coulee has flowed and spread out over the adjacent plain. On approacliing the Cinder cone one finds the surface, I ! ••i mn it: 230 VOLCANOKS (JF NoltTll A.MKUICA where not occupied by lava, to l)e covered with soft, dull, black, volcanic sand. At iirst this deposit is only a few inches thick, l)ut near the base of tlie cone it becomes Cijarser and deei)er. What thickness it attains in the immediate vicinity of the C(jne is unknown, but one- fourth of a mile away in all directions, it is about seven feet d p and decreases in alnuidance gradually so as to disappear at a distance of eight miles. Encircling the Cinder cone at its base, is a collection of volcanic bombs, ranti;inti; in size from a few inches to eight feet in diam- eter. They are nuich fissured, and many of tiiem have fallen to pieces, showing an interior of compact lava, while the surface is somewhat scoriaceous and ropy. On clind)ing the Cinder cone, one finds it to be com- posed of loose scoria and Lipilli. In I'oi-m and composi- tion and in fact in all its essential features, it reseml)les the summit portion of Vesuvius. The cone is regular in form, with a surprisingly smooth, dark surface, and shows no traces of waterways or other evidences of erosion. It rises to an elevation of 640 feet above the lowest point at its base, which is 0007 feet aljove the sea. Its diameter at the base is 2000 feet and 750 feet across the truncated summit. The slopes are as steep as it is possible for the material of which it is composed to lie, and in places is marked by slides. The angle of slope varies from 30° to 37°. The dull, sombre aspect of the smooth, barren slope is greatly relieved ))y carmine and orange colored lapilli on its southeastern side. At the summit of the cone, as shown in the following illustration, there is a well-developed crater with a double rim. The central funnel-shaped depression is 2-40 feet deep. VOLCANOES OF NOKTH AMKHICA. I'l.ATK 11. " \\; ■ \ ', <>•. I I 4*'.^,!ffm\ \ \ illy p 'kr^-K'- / / ! OLDEST LAVA. A>.C i UAPILLI. Ac. . ": L*VA PARTLY COVERED rin^a^ INFUSOH *L EARTM f- >< "^ nF iVC ' '-'*^'» j I SCALE OF FEET ■ 1000 " ""20'ia Geological ii»a|» nf tlic ("iiMler cone n\iTioii, ralifoniia. (J. S. Diilcr. •f '1'-' fi! til * (< i il ! ini t r r H 5 I' f - 5 P VOLCANOES OF THE UNITED STATES 231 Tlie lava field about the Cinder cone has an area of about two and one-third square miles, and at its borders terminates in precipitous scarps, m places over 100 feet high. Within the lava lield and about its borders in certain places, there are deposits of soft white diatoma- ceous earth. This is a lacustral deposit, composed largely of the siliceous cases of unicellular plants, known as diatoms, and is at least ten feet thick. The ))earing of this deposit on the history of the volcano will be seen in the followii.g summary, published Ijy Diller, in the geo- Fij;. 10. Sketcli of the crater of the cinder cone near Lassen's peak, (Jalifornia, sliowin.u the i)eciiliar feature of two rings, of wliicli the inner one encircles u fnnnel 2-10 feet deep. (.1. S. Diller.) logical folio where the facts just enumerated are descriljed and discu.ssed.' " The facts just mentioned show that there were at least two periods of eruption from the Cinder cone, and that they were separated by a time interval sufficiently long to allow ten feet of infusorial (diatomaceous) earth to accumulate on the ancient bottom of Lake Bid well. The first period was characterized by a violent explosive eruption, which formed the Cinder cone and ash lield ; the second, by a quiet effusion of a large mass of lava. 1 J. S. Diller, " Geological Atlas of the United States " (published by the V. S. Geological Survey), Lassen peak folio. 18!)"). This folio contains excellent topographical and geological maps of the region about Lassen peak, and a condensed account of the geology of the region. 232 VOLCANOKS OF NOUTH A MEUICA It 'l\ !|iil li i I < '•The first eruption bugan witli au xplosion and the ejection of a great deal ot" light scoriaceons, almost punii- ceous material, blown chiefly by escaping steam from the upi)er portion of the molten lava (magma) in the throat of the volcano. Succeeding the explosion and the erup- tion of the pumiciform material, and continuous with it, came the volcanic sand, lapilli, scoria), and bombs. They fell about the hole from which they were blown, and by their accumulation built up the Cinder cone, which is C(jniposed almost wholly of fragmental material. " After the greater portion of the fragmental material had been ejected the magma rose in the Cinder cone, and l)ursting it asunder, flowed over the southeastern portion of its base. This effusion was accompanied and succeeded by a shower of sand, which may have given rise to the inner rim of the crater, and formed a thin coating over the lava already effused. Whether or not the effusion of the oldest lava and the succeeding shower of ashes belong to the closing stages of the first eruption is not easily de- termined, but it is certain that both preceded that long interval of quiet dtn-ing which the old lake beds were de- posited. This season of volcanic rest was probably at least a century long, for to accumulate ten feet of infu- sorial earth would ivquire considerable time. '' The new flow of lava, . . . occurred at the close of tlie lake-bed interval. The remarkable characteristic of this eruption as compared with the former was the entire absence of any explosion from the crater in connection with the effusion of so large an amount of very viscous magma, since the same vent at an earlier period had been the scene of a violent ejection. " Everywhere i!.\ the lava field one is impressed with !\V VOLCANOKS OF TIIK UNITED STATES 1233 !\^ the idea that the lava of tliis Ihial eruption moved slowly and with great diffieulty, repeatedly breaking its crust and pushing along as a great stone pile, presenting an abrupt terrace-like front on all sides. It is a typical ex- ample of a lava field formed by the effusion of a viscous lava on gentle slopes. Had it been highly liquid, like many of the other basalts in the same great volcanic field, it would have found egress at the outlet of Lake Bidwell, and stretched d(jwn the little valley for miles to the northwest. " The whole aspect of the Cinder cone and lava field is so new that one at first feels confident of finding historic evidence of its eruption. . . . Yet the evidence clearly demonstrates that the earliest eruption occurred before the beginning of the present century. " Its age is shown by the relation of the old and new forest trees to the volcanic sand of the first eruption. The living trees grew upon the top of the sand, but the dead ones in the foreground were standing at the time of the eruption, and instead of growing upon the sand, grew from the soil which now lives beneath it." The evidence furnished by the partially buried trees, etc., as stated by Diller, shows that the first eruption oc- curred some two hundred years and the second more than fifty years ago. i The Great Volcanic Mountains of Oregon and Washington Distant views of the Cascade Mountains show that they are dominated hy a series of giant peaks, some of which, as Mt. St. Helen's and Mt. liiinier, arc detached from [ t 1 1 1 1 n H ' )}' ! I I ; <' I) 2:14 VOLCANOICS Ol'" NUltTII AMKIIICA the main mass, while others an; intimately associated with the u[tlil't(Ml lava sheets which eomp(jse a large part, hut more especially of the southern half, of the range. The greater volcanic cones which form such a pnj- riouncetl and attracti\e feature of the Cascade region have never been carefully studied, and only a general ac- count of their more salient features can he given at this time. The peaks, referred to in the order of their occur- rence fi'om south to north, arc; as f(jllows; the ligure.s accompanying the names of the jteaks show their height above the sea in feet. They are: Mt. Pitt, 1)700; Mt. Mazana, 8223 ; Mt. Uiuon, 78S1 ; Mt. Scott, 712:] ; Three Sisters, Mt. Jefferson, 10,200, and Mt. Hood 11.22-3, in Oi-egon ; Mt. Adams, 1)070; Mt. St. Helen's, U7oO ; Mt. Rainier, 14,525, and Mt. Baker, 10,877, in Wash- ington. The conclusion that these peak.s are (d" volcanic origin rests, in some instances, on their general appearance, and their occnrrence in a volcanic region, rather than on defi- nite reports by skilled observers. The only ones, how- ever, in reference to which doubt may possibly be enter- tained respecting tlieir volcanic origin, are two or three of the more southerly ones in Oregon. None of the mountains named are examples of espe- cially fresh volcanic piles, although nearly all of them are known to have craters at their summits, or on their flanks. Like Mt. Shasta, they are for the most part the result of Tertiary eruptions, and have been modified by erosion to approximately the same extent in all cases. Superficially considered, — careful comparison being im- possible at pi'esent. on account of the lack of observations. J VOLCAN(.)KS OF TIIK INITKI) STATES •J:W — it would seem that tlic liistory of Mt. Shasta lias Ix-cn rc'[)eate(l, [irobahly with many minor variations in each instance, at a numl)er of localities along tlie Cascade range, and in its vicinity. Crater Lake, Oregon. — One of the most remaikaUle of the extinct volcanoes of North America, known as Mt. ^lazama, is situated in the Ca.scade Mountains. Oregon, tiiirty miles north of Klamath Laive, and is occu^jied by Crater lake. The mountain in wiiicli this lake is situated is thouglit to have ))een truncated hy the mehing and .subsidence of its sununit. which left a rudely circuhir cavity fi-oni live to six mik's in diameter. The lake is 02oD feet abcne the sea. is 11)75 feet deep and sur- rounded by nearly vertical walls ranging from t)()0 to 2200 feet high. The vast caldera is, then, al)out 4000 feet deep. The fact that the mountain has been truncated is shown especially by the character of the slo[>es that remain. These are scarred In i-adiating valleys of the same character as those on neighboring nuMmtains which still preserve their ccmical forms, but open abruptly into the central caldera. The streams that ilowed down these iror^es, and to which their excavation is mainly due, have been beheaded by the falling in of the crater walls. The outer slopes of the truncated mountain also bear evi- dence of glaciation. showing that before the great catas- trophe that removed its summit, it was ice-cnnvned and orave oriuin to radiating alpine glaciers of the same nature as those now to be seen on Mt. Shasta and Mt. Uainier, but descending to a lower level. Ai)parently the mountain has lost its summit since the Glacial epoch. An account of Crater Lake, accompanied by references to the writings of C. Iv Button, l)y whom it was made '■| m^sm. mp 1 230 VOLCANOES OF NORTH AMERICA ill' 1 , ' I n kiKJWii to gt'ulugi.sts and guograpliurs, is contiiincMl in a companion of tiio volunio before you.' Mt. Pitt. — In soutliern Oregon and about .sixty miles north of Mt. SJKusta rises a beautifully regular, volcanic (Mmo known as Mt. Pitt. Although of secondary rank when com[)are(l with several more lofty summits in the Cascade region, yet its summit and sides are snow cov- ered during the greater part of the year. As stated by Knunons,- there is a remnant of a crater at the snnnuit, the walls of which are broken down, especially on the north- east side. The lavas that have been dischai'ged from the crater, or from secondary openings on its sides, resemble, in general, those poured out at Mt. Shasta, but present certain peculiar features that promise interesting re- sults when studied in the light of modern petrographic methods. Three Sisters and Mt. Jefferson. — To the north of Mt. Pitt, — as stated in the instructive paper by Emmons, cited above, — and in the main line of the Cascade Mountains, the group of volcanic peaks termed the Three Sisters, and a neighboring cone, Mt. Jefferson, mark the sites of still other ancient volcanic lights. Little accurate infor- mation is available concerning these attractive mountains, except that they are of volcanic origin, although now 1 I. C. Russell, " Lakes of North America," Ginn & Co., Boston, 1895, pp. 1*0, '21, and map. A map of Crater Lake with descriptive text and illustrations has been published by the U. S. fJeolo<;ical Snrvej-, with the title " Crater Lake Special Map." A highly instructive paper on Crater I^akes, by J. S. Diller, may be found in "The American Journal of Science" for March, 18f>7; and in a more popular form in the " National Geographic Magazine " for February, 1897. 2 S. F. Emmons, " The Volcanoes of the United States Pacific Coast," in American Geographical Society, Bulletin No. 4, 1870-77, p. 40. ill it VOLCANOKS (•! N(iUTI[ AMKIM. A. I'l.ATi: I.'. Fkj. a. Mt. IIihhI. OrcL'oii, lonkiiij: f-nst, April, isii,". (riiiili>L;i';i|ili liv (lillcinl iiii IImIi', I'driliiinl.i l''u). H. Fuiiiiirole in siiow-tilleil iiatcr of Mt. Hooil, Orej^on, July, ia!i4. (M. \N . (ionuaii.) A ^^'^^ <^ **'*' ^ IMAGE EVALUATION TEST TARGET (MT-3) /. ii 1.0 [f 1^ ll£^ ^^ g B,^ |22 2f lag ■" i.l s. 1*^ '^ 141 L22 III U B 1.6 n ^/. ^14 o / Photographic Sciences Corporation 23 WfST MAIN STREET WEBSTER, N.Y. MSSO (716)872-4503 4r %o 4^ # s mmmmoam^mmaa ,f f. i' i\ VOLCANOES OF THE UNITED STATES 237 cold and silent, and much modified by erosion. They form most beautiful features in the ma^milicent scencrv of Oregon. Their tapering summits, when snow covered, present striking contrasts with the sombre green of the pine-clad mountains and hills with which thev are siir- rounded. It is now known from exi)loration conducted by J. S. Diller, thai glaciers of considerable size occupy sheltered valleys among the clustering summits of the Three Sisters. Mt. Hood. — This majestic mountain, 11,225 feet high, is stated by Emmons to have the most graceful outlines of any of the justly famed volcanic peaks of the north- west coast. It rises from the very crest of the Cascade range, in northwestern Oregon, and about twenty-live miles south of the Columbia River. From the city of Portland, it forms the crowning summit of a far-reach- ing landscape. Something of the grandeur of this moun- tain, which bears a similar relation to Portland that Vesuvius does to Naples, may be gathered from the accompanying illustration (Plate 12, Fig. A). Its lower slopes, as is the case of all the lofty peaks in Oregon and Washington, are densely forested, and form an ideal setting for the dazzling cone rising above them. Could an observer obtain a bird's-eye view of the Cascade Mountains, they would appear as a belt of emerald studded at irregular intervals with immense brilliants. When the English explorer, Vancouver, who gave Mt. Hood its name, first saw the mountain, he estimated its height to be at least 25,000 feet, and thought it was per- haps the highest summit in the world. Barometric and other measuroments, however, made by the United States Coast Survey and by the Fortieth Parallel Survey, have ! I- t 1 i ri! Ml H\ f .i ■i" m II i III ' M J I 'I* ;:l 'ffi 2?.H VOLCANOES OF NORTH AMERICA sliown that Vancouver's estimate was more than twice the actual height. In spite of the corrections that prosaic measurements have iniposed upon the fancy of distant observers, Mt. Hood, if not the most lofty, is, yet, in the eyes of its admirers, one of the most beautiful of mountains. The summit of Mt. Hood, like many other similar peaks in the same region, retains only a portion of the walls of the original summit crater. It was ascended in 1888 by M. W. Gorman, a member of the mountain club (Maza- mas) of Portland, who reports that there are still fuma- roles on the northeast slope, and steaming rifts on the south side near what is known as Crater rock, at an ele- valion of about 8500 feet above the sea. The sulphurous fumes from these openings are sometimes so strong as to be overpowering, and will discolor silver at a distance, in the direction the wind is blowing, of half a mile from where they issue. One peculiar phenomenon, shown on Plate 12, Fig. B, is the occurrence of a fumarole in the deeply snow-filled crater. The actual summit of the mountain consists of a single block of lava only a few feet square, from which one may look down almost perpendicularly for thousands of feet on the north, and in other directions the descent into the forests far be- low is almost as precipitous. In the shelter of the peak on the north side, where the walls circle round what is stated to have once been a crater,^ clouds frequently col- lect even on clear days, and from time to time rise above the peak so as to make it seem as if steam was still issu- ing from the summit. So deceptive is this appearance ' This great depression has certain features which suggest that it is an amphitheatre of glacial origin. i^ VOLCANOES OF NORTH AMKRIf.V. I'l.ATi: i; Fig. a. Mt. St. Helen's, ^Vilsllingtl)ll. (M. \V. (ioniian.) Fici. B. Mt. Kiiiuier, Wasliiiistuii, Iroiii the soutli. (l'liuli)g!"ii>li Ity Brims, .Seattle.) I. I ■ ' 'i' ; rt It. i 1 1 II!' m m 'f'-i 1 i'i -M . t VOLCANOES OF THE UNITED STATES 289 that reports are fre([ueiitly iiKide of an eruption. As sliown by Arnold Hague, who has examined the sum- mit, no eruptions have taken place vvitiiin many years; and certainly not within the memory of man. To jud^^e from a distant view, as well as from the reports of those who have trodden its dizzy heights, it is a typical example of a volcanic mountain that has passed its prime and is slowly yielding to destructive agencies of the atmosphere. It is stated by George Gibbs ' that stumps of trees occur in abundance on the side of Mt. Hood above the present timber line, suggesting that formerly the heat of the mountain was sufficient to encourage the growth of for- ests at an elevation which was impossible when the moun- tain became cold. That this is the true explanation of the former extent of timber growths seems doubtful, in view of the antiquity of the later eruptions as de- terudned by careful observers who have examined the mountain. Mt. Adams and Mt. St. Helen's. — About thirty miles north of the Columbia and sixty miles from Mt. Hood, stands Mt. Adams, one of several great mountains oi which the people of Washington are justly proud. Mt. Adams is seen to the greatest advantage from the eastward, as it stands well to the east of the crest of the Cascade range. Several fine views of its deeply trun- cated summit and of its scarred slopes were obtained by the writer while studying the geology of central Wash- ington, in 1893. Its shape is that of the frustum of a cone. If its sides could be prolonged upward, they would meet at least a thousand feet above the present flat-topped summit. Whether the breadth of the summit is due to 1 American Geograpliical Society, Transactions, Vol. IV, 1874, p. So'i. •^'W^i^^'' 240 VOLCANUKS OV NUllTII AMlilllC'A ifh the grctat size of the original crater, to the blowing away of the top, or to some other cause, has not \ievn deter- mined. Although comparatively easy of ascent, it has not received the attention it deserves, and so far as I am aware, no competent observer has examined its summit. On tlie west of the Cascade and like Mt. Adams, stand- ing at a distance from the crest of that range, is another outpost of the mountains, known as Mt. St. Helen's. The country between these two peaks is rugged and heavily forested. Mt. St. Helen's (Plate 13, Fig. A), in contrast with its companion on the east, has a more regular conical form and is said to rise from all sides to a, comparatively sharp apex. Photographs of the peak fail to sliow^, how- ever, that it is more regular or fresher in appearance than its companion. Its reported conical form suggests that it is younger than Mt. Adams, although, as mentioned above, the truncation of that mountain may be due to an explo- sion and not to weathering, in which case its general form would not be an index of advancing age. If the statements of frontiersmen can be relied upon, Mt. St. Helen's is not only young, but has been in a state of activity within the past fifty years. Emmons says in his essay on the volcanoes of the Pacific coast, already referred to, that this mountain is the only one in the far Northwest concerning which he was able to obtain a definite account of a recent eruption. He was told by a French Canadian voyageur, that it was in active eruption during the winter of 1841-42. As stated by the gentle- man referred to, the light from the volcano at the date mentioned was so intense that one could see to pick up a pin in the grass at midnight near his cabin, some twenty miles distant. Mr. Emmons did not visit the jiii VOLCANOES OF THE UNITED STATES 241 mountain, but states tliat with tlio aid of a field-glass he could distinguish the ai)parent track of a lava How which had cut its way through many miles of tiie forest that clothes the mountain's sides. Mr. M. W. Gorman has informed me that he ascended Mt. St. Helen's in 1881), and found fumaroles on the north east side, but no steaming crater, although, as he states, the volcano seems to have been active in recent years, and is fresher in appearance than Mt. Hood. Lava has flowed northward from the mountain for about twenty miles, in some places passing through a forest of Douglas fir, and at certain localities cooled about large trees so as to take a cast of their charred and seamed trunks. The trees have since disappeared, leaving well-like openings which still remain unfilled. Specimens of the lava-casts of the bark of one of the trees thus surrounded has been sent to me by Mr. Gorman, and is a most interesting specimen. He states also that in one place the lava dammed the end of a canyon and led to the formation of a lake which is still without an outlet. When the last eruption took place, the lava appears to have flowed over wet places and the steam generated, escaped at the sur- face, leaving what are termed " blow holes." Mt. Rainier. — For many reasons Mt. Rainier is con- sidered by admirers of the beauties of mountain scenery, the finest single peak in the United States, not including Alaska. The secret of its grandeur is not so much its exalted height, 14,525 feet, although it is the loftiest summit on the northwest coast, but its isolated position, and because it rises practically from sea level. It is one of the few mountains in which the visual height, or the part that rises above the observer, is from many mm II ». I I I ll, 'i > M ' V i n « I' I, i. ■ r '< 242 VOLCANOES OP NORTH AMERICA points of view nearly the same as the actual elevation of the suuiniit above the sea. Mt. Rainier is in plain view from Piiget Sound. From the city of Tacoma, its shining summit is wonderfully attractive (Plate 14). Other elements that combine to make Mt. Rainier both picturesque and sublime are the dense evergreen forests that cover the country about its base and extend far up its rugged side, the perennial snow that crowns its sum- mit, and its fine glaciers which descend far into its encir- cling forest. The first ascent of Mt. Rainier seems to have been made by Messrs. Hazard Stevens and P. B. Van Trump,^ who after many hardships reached its summit in August, 1870. In October of the same year, Messrs. S. F. Emmons and A. D. Wilson of the United States Geological Exploration of the Fortieth Parallel, also made the ascent. The report of this highly successful expedition contains, so far as I am aware, about all the published observation concerning Mt. Rainier that are of value to the student of volcanoes.'' A few selections from this interesting report will enable the reader to picture some of the salient features of the magnificent mountain which still awaits detailed explora- tion and careful study. " Under the guidance of our Indians, a comparatively easy though rather moist march of a day and a half brought us finally on to the crest of the spur east of the Cowlitz River. As we gradually emerged from the forest region on tO the more open ridge, where grew only isolated clumps of mountain fir and huckleberry bushes, the rain- » "Atlantic Monthly," Vol. 38, 1876, pp. 513-530. 2 S. F. Emmons, " The Volcanoes of the United States, Pacific coast," American Geographical Society, Bulletin No. 4, 1876-77, pp. 31-61. :..■*=•-' VOLCANOES OF THE UNITED STATES 243 clouils whioli had oiiclosod us for tlio past three days l)roke away, and disclosed another superb vie'v of tlie mountain, now (piite near us, and yet seemingly UKjre lofty and inspiring than ever. '• The details of its surface were now visible. The very sununit was marked by a thin horizontal black line which we later found to be the rim of the crater. Below this stretched a smooth unbroken envelope of white, a[)parently about a third of the way down ; then, at irregular dis- tances along its sides, peeped out black shoulders of rock between which were deep broken masses of glacier ice, looking like foaming cascades frozen in the instant of their fall. This lower two-thirds of the peak was the steepest of all, and below it the glaciers, taking the form of rivers, flowed out at more gentle angles, gradually hidden in their ever-deepening beds between the grassy spurs." A day or two later the summit was reached. '' We stood upon the edge of a bowl-shaped crater of al- most perfect circular form, forming the eastern edge and highest point of the mountain, its interior filled to within thirty or forty feet of the rim with ice and snow, while on its outer slopes the blackened lava, of which it is com- posed, was laid bare for a hundred feet or more below the summit. This was the delicate black line, which we had sometimes been able to distinguish from below, as form- ing the summit. Adjoining this on the west was another semicircular rim of rock, peeping out of the snow, the remains of a former crater, in the interior of which this more recent one had built itself. It was strange to see even these comparatively small patches of rock free from the universal covering of ice and snow ; the explanation first presented to the mind was their exposed position, h ■*N«r \ 244 VOLCANOES OV NOUTII AMERICA ;!' I 1 and the trtMiiundoiiH force of the wind, whicli seemed ulniost sutliL'icnt to blow away the rocks. A second was soon seen in tho evidence of internal heat at no great dcptli below tlie snrface, shown by countless jets of steam and gas of size from a pinhcad to an inch in diameter, issuing .iround the interior rim of the crater. Near the.se j(,'ts the hard rock is changcid into a red clayey mass and in front of them, by the condensatiim of the steam, ice caverns have been formed, some of sufficient size to admit several persons. In one of these we took refuge for a few moments t(j warm ourselves and thaw our fingers, two of mine being sli;5htly frozen. . . . "From our sunnuit we could see the two other peaks, only a few hundred feet lower than ourselves, the one to the southwest, and the other northwest, from one to two miles distant, and separated by the heads of a deep valley filled by neve ice, which sloped rapidly to the westward between the two peaks. It was evident that this valley was the interior of a still older and larger crater, of the walls of whicli these two peaks are the renmants. The crater npon which we stood had been built up as an in- terior cone entirely within the wall of this older crater, and the outstanding pinnacles of rock on the east, which we had observed on our first day's climb on the glaciers, must be the >nly remnant left of the east side of this outer cone ; over a third of the mountain mass had been carried away and that largely by the energy of glacier ice. "From the northeastern rim of the crater, we could look down on an unbroken slope of nearly 10,000 feet to the bed of White River, the upper half or two-thirds of which was so steep that one had the feeling of looking |WiiWh¥iiMWWWiiiliWiifHfr»»B)in«| n I VOrX'ANOES OF XOHTH AMKRICA. - 1 • 'v" *W* »** ,.;**> Mt. Rainier, Washington, from near Tacomn, looking southeast, J PLATE 14. icomn, looking soutlienst, June 14, 1896. (Photograph by A. H. Wliite, Taconia.) VOLCANOES OF THE UNITED STATES 24o over a perpendicular wall. The system of glaciers, and the streams which flowed from them, lay spread out as on a map at our feet ; radiating out in every direction from the central mass, they all with one accord crossed to the westward, to send their water down towards Puget Sound or the lower Columbia River.' " Looking to the more distant country, the whole stretch of Puget Sound, seeming like a pretty little lake embowered in green, could be seen in the northwest, be- yond which the Olympic Mountains extended out into the Pacific Ocean. The Cascade Mountains, lying dwarfed at our feet, could be traced northward into British Columbia, and southward into Oregon, while above them, at com- paratively regular intervals, rose the ghost-like forms of our companion volcanoes. To the eastward the eye ranged for hundreds of miles over chain on chain of mountain ridges, which gradually disappeared in the dim blue distance." Mt. Baker. — The most northerly of the volcanic piles connected with the Cascade Mountains south of the United States-Canadian boundary is Mt. Baker. What the char- acteristics of the north extension of this volcanic belt may be, remains to be discovered, but at present no recent vol- canoes are known in the re";ion immediately to the north of the international boundary. Concerning Mt. Baker, little can be said. It rises from the dense forest that extends from the Pacific coast east- ^ An account of these glaciers may be found in "Glaciers of Xorth America" by I. C. Russell. Ginn & Co., Boston, 1895. pp. G2-67. The writer ascended Mt. Rainier, in the summer of 1896, and passed a night in one of the craters at the summit. A report on the glaciers visited will be published in the 18th Annual Report of the U. S. Geological Su-vey. A popular account of the expedition will .appear in " Scribner's Magaz'iie." I( T 246 VOLCANOES OF NOllTII AMERICA "i» ward to beyond the Cascade Mountains, and is fully twenty-five miles west of the crest of the main range. From Puget Sound it is in full view on clear days and appears as a conical peak which from its form is at once seen to be of volcanic origin. From the north and east especially its summit appears to be truncated. Whether this is due to erosion or to volcanic explosion has not been determined. Gibbs ^ states that he v;as informed by officers of the Hudson Bay company and also by Indians, that Mt. Baker was in eruption in 1843, and that "it broke out simultaneously with Mt. St. Helen's, and covered the whole country with ashes." It was reported that during this eruption, a neighboring river, the Skagit, was ob- structed and all the fish in it died, and also that " the country was on fire for miles around." The truth of these reports is to be taken with some reserve, however, since a fire on the mountain might be mistaken by un- skilled observers for a volcanic eruption. The Cascade Mountains The Cascade Mountains extend from northern California northward, with a nearly north and south trend, across Oregon and Washington. At the south, the range termi- nates in the Lassen peak volcanic district, already briefly described ; its northern extremity has not been definitely ascertained, but is probably not far north of Mt. Baker. In round numbers, the length of the range is 500 miles, and its average width about fifty miles. In general, it is ^ George Gibbs, " Physical Geography of the Northwestern Boundary of the Unitea States," American Geographical Society, Journal, Vol. IV, 1873, p. 358. T VOLCANOKS OF THE TXITKI) STATES 247 parallel with the coast line of the Pacific, 120 niilos dis- tant from the crest of the range at the south, and 200 miles at the north. The crest line, althou":h irreiiular in height, is in general from 5000 to 8000 feet above the sea, and is broken by several passes, more espe- cially in the northern half. The deepest gorge, and the only one which permits the drainage of the interior to cross the uplift to the Pacific, is that through which Columbia Ptiver flows. It is frequently stated or implied, that the Cascade Mountains are comjajsed mainly of lava, and that the range owes its prominence to the accumulation of succes- sive sheets of this material, which have flowed from vents near the crest of the range, and cooled and hardened so as to build up a great ridge. If my understanding of this hypothesis is correct, the Cascade range is considered to have originated in much the same way as certain iso- lated volcanic mountains, like those of the Hawaiian islands for example, in which successive overflows of molten rock have been piled one above another. Under the hypothesis referred to, one is led to infer that many mountains of the Hawaiian type have been formed along a line of fissures, and that their lava sheets interlaced so as to form a much elongated ridge. It has been stated, also, that the Cascade Mountains differ from the Sierra Nevada, in that the former have the general structure just mentioned, while the latter owes its leading features to the uplifting and tilting of long, narrow^ blocks of the earth's crust adjacent to faults. Although the structure of the Cascade Mountains has not been systematically studied, and any positive conclu- sions in reference to the mode of origin of the range 1 1 " \\ M "W II ! n w I- I: u iti'i 1 (■ 1.- '1.(1' 248 VOLCANOES OF NOIITII AMERICA would be premature, yet there are several facts known whicli are inconsistent with the hypothesis just stated and point to another explanation. During two expeditions conducted by the present writer in the region adjacent to the Cascade Mountains on the east, one in Oregon and the other in Washington, the eastern border of the range was examined. The mono- clinal structure so characteristic of the western portion of the region, known as the Great Plain of the Columbia, and of its southern extension in the Great Basin, due to the tilting of fault-blocks, was found to extend to the mountains on the west. As one approaches the Cascade range from the east, the tilted blocks, the up- turned edges of which are short mountain ridges, become of larger size, and form the immediate foothills of the main range. This merging of the structure characteristic of the interior basin with the mountains bordering it on the west, so far as my own observations extend, is more pronounced in central "Washington than elsewhere. From what I have seen of the Cascade Mountains I venture to suggest as a working hypothesis, that the lava composing them, more especially to the south of Lake Chelan in Washington, is an extension of the Columbia lava — described a few pages in advance — which covers such a vast area in the eastern portion of Oregon and Washington. This lava was poured out in successive sheets and afterward broken over extensive areas, by fractures, and the blocks thus formed tilted at various angles. The hypothesis here suggested assumes that the Columbia lava extended over the Cascade region in origi- nally horizontal sheets, and was, subsequently, broken and VOLCANOES OP THE UNITED STATES 240 tilted. Tlie structure of the Cascade Jilountains, under this hypothesis, is therefore not different in its main feat- ures from that of the Sierra Nevada. Tlie Cascade Mountains are not composed wliolly of hiva, as seems to ha the prevaihng idea, derived appar- ently from reconnoissance in their soutliern portion. Be- neath the lava in central Washington, there are Tertiary rocks, and highly metamorphosed beds of unknown age. These basement rocks share in the disturbances that have affected the lavas resting on them. Much of the nortliern portion of the range is free from lava, and differs in a marked way in all its scenic features from tiie heavily lava-covered portion to the south. In the northern por- tion, the rocks are largely granite and schist, showing at once that to ascribe a volcanic origin to the range, as a whole, is inadmissible. The great volcanic peaks described in the past few pages are of later date than the uplifting of the main Cascade range, and probably owe their origin to the es- cape of molten material through fractures formed at the time the mountain blocks were separated one from an- other by fractures, and severally upraised. Of the two hypotheses that the reader now has be- fore him, the first, namely, the one which refers the origin of the Cascades to volcanic overflows, finds its greatest support in the southern portion of the range ; while the second, or the one that seeks to explain the main topographic features of the mountains by fracture and upheaval, applies more particularly to the central and northern portions of the same mountain belt. When the Cascade Mountains have been thoroughly explored, it may possibly be found that each of these hypotheses is il I! I'i^ ' I'r 1 1 !f ■I 250 VOLCANOES OF XOUTH AMEUICA in part correct, and that the range is less simple in struct- ure than is now supposed. CoLUMiJiA Lava Merging with the Cascade Mountains on the east and extending through Washington and Oregon, far into Idaho, there is a vast lava-covered country, which is with(jut prominent points of eruption. In fact, cinder and lapilli cones of any description are almost entirely absent. The boundaries of this lava-covered region have never been traced except for a few score miles in north- central and eastern ^yashington, but it is estimated to have an area of from 200,000 to 250,000 square miles. The region most nearly comparable with it is in India, previously referred to, where the Deccan trap covers ap- proximately the same area. These two great basaltic areas have also many points in common in reference to the character of the rocks composing them, the manner in which the lava occurs in sheets interstratified with lacustral sediment, etc. The Deccan trap is thought to be of Cretaceous, while the Columbia lava is of Tertiary age. The Columbia lava is not one vast flow, but is com- posed of many independent sheets, which are sometimes separated by land surfaces containing the stumps of trees and even huge trunks buried in lapilli and now thoroughly silicified. The lava sheets overlap and supplement one another so as to form a continuous and highly compound system. No single sheet can be traced over the entire field, but yet in the sides of the numerous deep canyons that have been eroded in the lava, individual flows can frequently be followed for a score or more of miles. The 'W^ VOLCANOES OF TIIK UNITED STATES 251 series varies in thickness from a few score feet at cer- tain localities on its l)or(lers, to over 4000 feet in south- eastern Washington, where it has been (leei)ly dissected l)y Snake River, without, however, revealing its niaxinnnn vertical extent. In the walls of the canyon cut l)y the Cokunl)ia, according to Le Conte,' the aggregate thick- ness of the many lava sheets exposed is o700 feet. Its average thickness is thcjuglit by Symons- to lie not far from 200o feet. My own observations suggest that this estimate is too low, but no conclusion of nuich value in this connection can be reached until more exten- sive surveys have been made. Many sections of the Columbia lava were seen l)y me in Washington and Oregon, the most instructive being along the Columbia and Snake rivers and some of their tributaries in Washington. The rock is usually a black basalt, with frequently a well-defined columnar struct- ure, but at times is also highly vesicular and scoriaceous, especially on the surface of the sheets. Many times the marked columnar structure recalls the finest of the basaltic columns so well known at the Giant's Causeway and on the Isle of Staffa. The walls of the canyon cut in the lava are similar to the Palisades of the Hudson, but are far more extensive and usually exhibit several distinct colonnades one above another, which can be fol- lowed for scores of miles. As previously stated, there is a general absence of cones of eruption throughout the region covered by the Colum- bia lava. In view of the original extent of the lava 1 " American Journal of Science," Vol. 7, 3d series, 1874, p. 168. 2 " Report of an Examination of the Upper Columbia River," Washing ton, 1882, 47th Congress, 12th Session, Ex. Doc. No. 186, p. 100. I p ■ii V \' 1 m i'l! VOLCANOES OP NOHTFI AMKKICA westward, montionod above, namely, that it includes the region of the (Jascade Mountain.s ; tlie great volcanic peaks like Shasta, Rainier, etc., nnist be considered as points of eruption from which some of the lava flows originated. The flows from these craters, however, arc comparatively small in volume, did not spread widc.'ly, and in part are of more recent origin than the main body of the lava sheets with v.hicli they are associated. The absence of cinder cones, lapilli craters, etc., over all of the region covered by the Columbia lava east of the Cascade Mountains, from which the great lava sheets could have been derived, has led to the conclusion, first suggested, I believe, by Roichthofer, that the lava came to the surface through fis.sures, in a highly fluid condition and spread widely over the country without forming vol- canic mountains. This conclusion is sustained by obser- vation made by me on the eroded edge of the Columbia lava, about twenty miles west of Ellensburg, Washington, where the border of the lava has been removed and a deep valley formed, the eastern wall of which is capped by the lava, which rests unconformably on sandstone and shales. In the sedimentary rocks beneath the lava cap, there are large dikes that lead up to and merge with the lava forming the surface. These dikes show that the surface lava, in part at least, came through large fis- sures and spread out in sheets over the land. Near the upper surface of the Columbia lava in central Washington, near Yakima, there is a thin layer of clay formed as a sediment in a Tertiary lake and subsequently covered by a lava flow a hundred feet thick. Above this bed of basalt and resting evenly on its surface are gravels and fine, evenly bedded lacustral sediments, having a VOLCANDKS OF THE UNITED STATES 2');] tliickness of 125 foot; next abovo is an interstratilii'd sheet of coliininar basalt, varyiiii^ from 40 to lOU feet in thickness, which may bo traced in an east and west direction for 75 to 100 miles. Above this widely spread sheet are lacustral sediments known as the John Day system, whicii in places is rich in the remains of large mammals, showing it to be of Tertiary age. Many sections of the lava and of inters! ratified lacustral sediments, show that a period marked by great volcanic overllows ended in a lacustral period during which an ex- tensive region to the east of the Cascade Mountains was occupied by a great lake, or perhaps a series of large lakes of Miocene age, in whicli hundreds of feet of line sediments were deposited. These records furnish evidence that the main inundations of lava occurred somewhere near the middle of the Tertiary period, and not during the Glacial epcjch, as some writers have supp(jsed. That the lava is of older date than the Glacial epoch is also shown by the fact that in places its surface has ])een smoothed and striated by moving ice and is covered with moraines. The lava does not form a vast unbroken sur- face, but, especially in central Washington and in central Oregon, has been disturbed by orographic movements and deeply dissected by streams since the last addition of molten rock was made to the series. These changes in topography increase in extent as one travels westward from the eastern margin of the lava-covered country and culminate in the Cascade Mountains. In southeastern Washington the Columbia lava has been but slightly disturbed over an area of several thousand square miles, and furnishes an example of the leading characteristics of the vast lava-covered reoion of which it I 1 li hJ 254 VOLCANOES OF NOKTII AMEUICA I ' lii '* k" '5: ;*v IV I ji ! is a part, after tlu. final outpouring of niolton rock and buforo tlio ))U{].s wore fracturcMl and uplicavtMl. The lovt'l surface of the l)asaltic plateau meets tin; nioantains of older rock in nuurh the .same maimer that th«' ocean joins a rugged and deeply iiulented coast. The molten lava entered the valleys and gave them l(!vel floors of basalt ; the deeply scul[)tured ridges between the valleys were transformed into capes and headlands; outstanding moun- tain peaks became islands in the sea of molten rcjck. One of these island-like mountain peaks, known as Step- toe butte rises 1000 feet above the surrounding plateau and is about twelve miles distant from the shore of the once fiery sea. Snake River tlows across the basaltic pla- teau and has excavated a magnificent canyon some 4000 feet deep and fifteen miles broad. Within the canyon there are numerous lateral ridges and a multitude of striking architectural forms due to erosion. The excava- tion of the canyon has revealed the summits of angular mountain ranges that were surrounded and finally buried by the successive inundations of molten rock. One of these buried peaks rises about 2500 feet above the river and is covered by fully 1500 feet of horizontally bedded basalt. These are but a few of the facts that have been observ^ed which demonstrate the extent and character of the vast fissure eruptions that occurred from time to time during tens of thousands of years in the far northwest. The surface of the Columbia lava is covered with deep, rich, residual soil which has resulted from the slow disin- tegration and decay of the basalt, and furnishes the mar- vellously productive wheat-lands for which Oregon and Washington are justly celebrated. In autumn the bound- less plateau is a golden sea of waving grain. VOLCANOKM OF THE I'MTKI) HTATE.S 255 • Tlio conditions prosontcd on tin* eaMtorn Itorilor of tho Colimiliiii liiv.i in Idaho, Jin; thus doscrihcd by (Ii'ikii':' "Wo found that tlu; older trachytic lavas of the hills had biiun deeply trenched hy lateral valleys and that these val- leys had a lloor of the black basalt that had been poured out as the last of th(! molten materials from the now extinct volcanoes. There were no visible (rcnies or vents from which these floods of basalt could have jiroeeeded. We rode for hours by the margins of a vast plain of basalt, stretching southward and westward as far as the eye could reach. It seemed as if the plain had been once a great lake or sea of molten rock which surged along the base of the hills, entering eveiy valley, and leaving there a solid floor of bare black stone." Westward the general conditions observed by Geikie extend through Idaho, Oregon, and Washington, but the westward flowing streams, and particularly Snake River, have made deep channels in the lava, so that crossing it in a straight line is impossible. On the Great Plains of the Columbia in central Wash- ington, there are many deep canyons termed coulees which have been eroded by streams, along lines of faulting. The most remarkable of these, and one of the most noticeable topographic features of the region, is what is known as the Grand Coulee.'^ This is a trench across the lava with vertical walls from 300 to 400 feet high, between which there is a flat-bottomed valley, from a mile and a half to four miles broad, occupied in part by * Archibald Geikie, " Geological Sketches at Home and Abroad, 1882," pp. 337, 338. * The word coulee is used in the far Northwest to dosiffnate a steep-sided valley or what in more soutli^rii states and territories would be designated as canyons. Coulee is also used to designate a lava flow. M N 256 VOLCANOES OF NOUTH AMERICA I.: I ■ m !l i' \< ' lakes, some of which are without oiitlett? and strongly al- kaline. Its length from the Columbia River at the north to Coulee City is about thirty miles ; its eastern wall then disappears and the level lloor of the canyon merges with the plain which extends eastward ; the western wall is continued for twenty miles farther and overlooks a nar- row but still wilder and more desolate vallej^ than that of the Grand Coulee itself, which is bounded on the east l)y another vertical wall that begins just south of Coulee City. The top of the east wall of the canyon tj the south of Coulee City is on a level with the bottom of the gorges to the north ; the descent from one portion of the coulee to the other is vertical, and over this rugged escarpment formerly rolled a river comparable with the Niagara. The great coulee (canyon) briefly described above, like many others of a similar nature, although of smaller di- mensions, in the same region, is due primarily to a fault- ing of the lava, and the enlargement of the break thus formed by river erosion. Central Washington is now an arid region in which no perennial streams of any consid- erable ma ^ VOLCANOES OF THE UNITED STATES 257 present site of Coulee City formed a magnificent cata- ract.* Volcanoes of the Coast Range At only a few points in the Coast Mountains immedi- ately bordering the Pacific in the United States, from the Olympic Mountains at the north to the Mexican boun- dary, arr» there volcanic rocks of recent origin. As the few extinct volcanoes that we know in this region furnish no features not already well illustrr^ted by the examples pre- viously considered, we can pass them by for the present with but a word. Dana^ has described an extinct volcano known as Saddle Mountain, in Oregon, about fifteen miles south of the Columbia. This is a crater now extinct and forest covered, that is about two miles wide and approximately 500 feet deep. Muir's butte in California, south of San Francisco Bay, is another prominent volcanic pile, which has been much eroded but still retains the gracefully curving slopes so characteristic of cinder cones. Volcanoes of the Rocky Mountains Although igneous rocks are abundant throughout the greater portion of the belt of rugged country known as the Rocky Mountains, but a few volcanoes occur there * An account of the Big Bend country in Washington, and of the west central portion of the region crossed by the Columbia lava may be found in " A Geological Reconnoissance in Central Washington," by I. C. Russell, U. S. Geological Survey, Bulletin No. 108. Reference to previous publications on the same region are there given. See also, I. C. Russell, " Reports on a Geological Reconnoissance in South- eastern Washington," U. S. Geological Survey. In press. 2 J. D. Dana, Reports of the Wilkes Expedition, " Geology," 1849, p. 644. v.m II i H li ■/-"Ti^^V rT'i" ' ,*(N^r M i 1:1' "'I M ;M I i^ 1 1 ' t' 1 h 258 VOLCANOES OF NORTH AMERICA which are sufficiently recent to retain their characteristic topographic forms. Much may be learned in this region, however, respecting the internal structure of volcanic mountains, and of the nature of their originally deeply seated roots, as they may be termed, for the rea3on that erosion has in many instances dis!:ected these ancient piles and laid bare their anatomy. Blackfoot Basin, Idaho. — In southeastern Idaho there are at least two or three small basaltic craters which still retain their characteristic shapes and are probably closely associated in time with the outflows of the adjacent Columl)ian lava. As described by A. C. Peale,^ one of these craters is a circular depression 130 yards in diameter and ten to twenty feet deep. Surrounding it is a rim of variously colored scoriaceous basalt fifty feet broad on its crest. The crater is of the nature of a parasitic cone, possibly originating from lava flowing over water, and is surrounded by a lava field. About ten miles distant is another similar crater, but not so regular and less well preserved. Other poorly defined craters, together with vesicular basalt and fine lapilli, are mentioned as oc- curring in the same region. Colorado. — The evidence of late volcanic eruptions in Colorado is summarized by F. M. Endlich "^ as follows, but the weight of evidence seems to assign the greater part of the eruptions mentioned to Tertiary tim.e : " A number of isolated basaltic eruptions occur in Colorado. Prominent iimong them is that of Golden City, where there are table mountains composed of lig- ^ Eleventh Annual Report of the U. S. Geological and Geographical Survey of the Territories (F. V. Hayden in charge), 1877, pp. 561, 562. * Tenth Annual Report of the U. S. Geological and Geographical Survey of the Territories (F. V. Ilayden in charge), 1878, pp. 250, 251. VOLCANOES OF THE UNITED STATES 2oO nitic beds covered with liiisalt. Mr. Marvine says with regard tliereto : ' The source of this lava is from beneath North Table Mountain, on the summit of which, and near the northwest corner, the remnants of a group of small volcanic cones may still be seen; weather-beaten and nearly worn away, they still suffice to show from whence the lava came.' This explains, in a few words, both the source of the basalt and the character of such eruptions. Not %r from Golden, at Valmont, a heavy dike of the same material may be observed. Inasnuich as we may safely regard isolated eruptions as the results of local dikes that have overflowed, that of Valmont deserves mention here." Two small basaltic cones near Canyon City are also mentioned. These have since l)een examined by the present writer and found to be much wasted cinder cones, which have lost the depressions that probably once existed in their summits. Worn and eroded as they are, they appear to be among the most recent eruptions to the east of the main Kocky Mountain uplift. A few other occurrences of basalt in Colorado are mentioned by Endlich in the report just cited, and in conclusion he says : "Although the basaltic eruptions have been pro- ductive of forms reseml)ling crater cones more closely than any of the other eruptions, not one occurrence has been observed in Colorado that could directly be compared to the cone and crater of an active or typical volcano." Spanish Peaks. — To the student of volcanoes, the most interesting mountains in Colorado are the Spanish peaks, situated in the southeastern part of the state, about sixty miles south of Puel)lo. There are two prominent peaks in the group referred to, which rise 12,720 and 13,620 feet, respectively, above the sea, — the adjacent valley 1 I 'It r i I ■ i' ■li! ■I II 1 260 VOLCANOES OF NORTH AMERICA has an elevation of about 5000 feet, — and present fine examples of the ruins of ancient volcanoes. These two peaks rise abruptly from a region of comparatively mild relief and on account of their isolated position are im- pressive from whatever direction they are seen, not only on account of their height, but because of their sculptur- ing and varied colors. They are sharp, conical peaks from which radiate a large number of narrow, wall-like ridges formed by dikes, which mark the courses of fis- sures. These dikes, now weathered out so as to stand in bold relief, extend from the plain up the mountains to their very summits. Neighboring volcanic tablelands give evidence that still other dikes and sheets of igneous material have crumbled away, leaving only isolated rem- nants. East Spanish peak is lower than its companion and also presents steeper outlines, more sharply cut slopes and ridges, but less of the characteristic dike-walls, than its neighbor. The main body of this beautiful mountain is composed of red sandstone that has been altered by heat, so as to produce a number of species of metamor- phic rocks. On ascending the western peak from the south, one passes over red sandstone, until near the tim- ber line (10.000 feet), where large masses of igneous rock are encountered. As described by Endlich : ^ " Fragments of numerous varieties of trachyte and rhyolitic trachj'te lay scattered about at the base of the mountain in great profusion. Vertical places are seen along the ridge we propose to climb, and on reaching them we find that they are caused by dikes. There are from two to sixty feet in thickness and not infrequently extend from near the 1 F. ^I. Endlich, Ninth Annual Report, U. S. Geological and Geographical Survey of the Territories (F. V. Hayden in charge), 1875, pp. 129, 133-136. }'■ i(l .i 1 VOLCANOES OF THE UNITED STATES ■2i:>i summit down into the valley for several miles. All the strata in their immediate neighborhood have been baked, and much metamorphosed. Near the top of the moun- tain the sedimentary Ijeds have totally disappeared and nothing remains but the trachyte brilliant with brown PMca, white oligoclase, and long^ shining needles of black hornblende. This cap of igneous rock rests on the sedi- mentary beds and, together with the numerous radiating dikes and the hardening of the sedimentary layers by heat and heated solutions, has preserved them from erosion." Evidently the highest summit of the Spanish peak is a remnant left by erosion. The ancient volcano has been completely removed. Only its roots remain. The west peak contains more trachyte than its neighbor, but this rock also rests on sandstone, and sends out a number of radiating dikes, which descend to the adjacent plain as conspicuous ridges. Some of the ridges radiating from the Spanish peaks show a remarkably straight course, while others follow irregular lines. Owing to the removal of the sediment- ary beds that once enclosed the dikes, the intruded rocks stand out in bold relief and can only be compared to Cyclopean walls. Two of these are specially mentioned by Endlich which are eight and ten miles in length, respectively, with vertical sides, several hundred feet high. In some instances the hardened sedimentary beds adjacent to the dikes also resist erosion, and each side of the central wall of igneous rock is flanked by a somewhat gentle slope composed of sedimentary beds. Transverse dikes also exist which cross those radiating from the central peaks at acute angles. Ramifications also occur in several instances ; the branches retaining ^^ik^MHi- . \ 2G2 VOLCANOES OF NORTH AMERICA i»i I. r I i the same size, however, as the dikes fiuiii which they diverge. Wherever creeks cross the protruding dikes, the ridges are l)roken through, but in no instance have they caused a deflection of the lines of drainage. More than lifty of the great dikes have l)een uiapi)ed, but there are many more that are not prominent topographic features and have escaped notice. Much more interesting and instructive information concerning the remarkable dikes is contained in the report cited above. In that report (page 135), 300 or 400 feet is given as an estimate of the amount of degradation over a large area, as shown by the prominence of the dikes that now form such a remarka- ble feature of the region. Students of erosion will now, I think, agree that these figures should be greatly in- creased. It seems to the present writer, from a study of the region adjacent to the Spanish peaks, as well as from the descriptions just cited, that 5000 or 6000 feet would be a small measure of the amount of surface material that has been carried away. The Spanish peaks have not only been reduced to the condition o^ volcanic necks, like those of the Mt. Taylor region. New Mexico, described on a previous page, but erosion has been continued until the necks themselves have been removed, and the ver}' roots of the volcano to which they lead laid bare. New Mexico. — The igneous rocks, which on account of their influence on erosion form marked features in the relief of southeastern Colorado, extend southward into N( w Mexico, and there become even move conspicuous. Many tablelands and isolated hills, or buttes, in New Mexico, owe their existence to summit layers of lava, which have sheltered and protected the sedimentary rocks l)eneatli. i i i W i ti r h i-V \\u iili . rr;-:r 266 VOLrANOES OF NOKTII AMERICA careful surviiy.s sliall liavi; been made. Tlic many feat- ures of inten.'st in the n.'gion studied l)y Stevenson form but a beginning of what may be expected in the future, but at present we shall have to leave this exceedingly instructive region, as accurate information concerning it is not available. Canada. — Kespecting the occurrence of recent vol- canoes in Canada, I am unable to give the student much assistance, owing to lack of recorded information. It is scarcely to be expected that the volcanic belt, lOUO miles broad in the United States, ends abruptly at the international boundary, and begins again in Alaska, but the reports of surveys that have been made in this mter- mediate country contain but meagre accounts of recent volcanic phenomena. The great source of information concerning the geography and geology of the vast region embraced in the Dominion of Canada, is the reports of the admirable Geological and Geographical Survey of Canada, issued at Ottawa. North of the region occupied by Columbia lava, de- scribed on a former page, there are vast areas drained by Frazer River, which are covered with similar sheets of basalt and in many ways repeat the conditions ob- served in the region draine ^ by the Columbia River. Future exploration may possibly show that there is a great northward extension of the Columbia lava, but so far as can be judged, the Frazer River area seems to be distinct. The lavas in this region rest on and are inter- stratified with Tertiary lake beds, and with beds of lapilli and volcanic dust ; their surfaces are glaciated and moraine-covered, thus showing that in a general way at least they are of the same age as the Columbia \ • 4» m^^:^ £aeimv^':jaM V0LCAN0K8 OF THE UMTKU HTATKS 207 I lava. Tho lava occur in .shoots which colloctivoly occupy an area of several tiiousand scjuaro niilos, but thoir boun- daries liavo n(!Vor boon surveyed. In describing the Frazor River region, DawsiMi states that no distinct traces of volcanic craters were ol).served, although important centres of extrusion are described.' No reports are known of volcanic eruptions in Canada within hist(jric times. Volcanoes of Ala.ska In Alaska, 'f ■i';W^'^"w^>.i' uMH«,7i..>|i»'i'<^u<('»''"«'? ■«i|«i»ipi>i>nM jwi|wn«r7Kii^ !: t 270 VOLCANOES OF NORTH AMERICA the height of which has never been accurately deter- mined. Mt. Wrangell is said to have been in eruption in 1819 ; and at the time of the most recent reports from that region, was still sending out a column of steam from its summit. Several lofty peaks in its vicinity are probably also of volcanic origin, but this has not been definitely determined. It is stated by Grewingk ^ that there is definite infor- mation of volcanic activity on twenty-five of the Aleu- tian islands. On these islands, forty-eiglit craters have been enumerated. In addition to these, there are at least four on the Alaskan peninsula^ two on the shore of Cook's Inlet, one on Prince William Sound, and at least one — Mt. Wrangell — on Copper River, making, together with Mt. Edgecumbe and Mt. Calder, fifty-seven active or recently extinct craters. This number will, no doubt, be increased when detailed explanations are carried out. Summaries of various reports, made largely by Russian explorers, concerning volcanic eruptions, earthquakes, hot springs, etc., in Alaska have been given by Dall,^ Gre- wingk,^ and Petroff*; the writings of these explorers, with the exception of Grewingk's travels, are easily accessible. Cook's Inlet. — The west coast of Cook's Inlet rises .lyi m I i Cited by Ivan Petroff in Report of Tenth Census, Washington, 1884, pp. 93-96. 2 W. H. Dall, " Alaska and its Resources," Boston, 1870, pp. 286-290, 466-470. 'C. Grewingk, "Beitrag zur Kenntniss der orographischen und geog- nostischen BeschafPenheit der nord-west-kiiste Amerikas, mit den anliegen- deu Inseln," Mineralogical Society of St. Petersburg, Proceedings, 1850. * Ivan Petroff, " Report on the Population, Industries, and Resources of Alaska"; in Reports of the Tenth Census, and of the Eleventh Census, Washington, 1881 and 1893. In I I'i :i^-irssapuJfWj»*wu5iKw 'I VOLCANOES OF NORTH AMERICA. ri.ATE 15. ■ »—>-W^- l".l Wf" 11 **"'^' \V« '-jpi'-V.^!'' -.--r-.,^^. .-^ fc=, •• Fio. A. Fiivloff. Alaskan Peninsula. {Phnt'i<;rapli by Lieut. \. L. Broaill)Piit.) Fia. B. Shishaldin, Alaska, from Berinjr Sea. (Photogiai)h by L'. S. Fish Conimis- siou.) w r «■■ bfwH ij f' ; i ■'. VOLCANOES OF THE UNITED STATES 271 abruptly from the sea and has two peaks of special prominence, known as Redoute and Iliamna, both of which are volcanic, and are reported to be about 11,000 and 12,000 feet high, respectively. Iliamna awakened from a period of repose in 1778, and has since kept in a state of mild activity with occasional explosive erup- tions. In describing a visit to Cook's Inlet, Dall ^ re- marks that it is only at a distance of thirty or forty miles that the majestic cone of Iliamna disengages itself from its associates and stands revealed in all its beauty. In the summer of 1895, when last seen by Dall, it was sending out five or six parallel columns of steam, and seemed peaceful enough. A few years ago, however, it was in violent eruption and discharged such a profusion of hot dust and lapilli that the timber over hundreds of square miles on the adjacent tableland was killed. As in the case of several of the recently active volcanoes of Alaska, the steam rising from Iliamna is usually so densely charged with volcanic sand and dust that it appears black. For this reason, the volcanoes are usu- ally said to "smoke," although, in reality, little, if any, smoke is present, but only dust-charged steam. The accompanying illustration of St. Augustine, for which I am indebted to the United States Geological Survey, will serve to show the leading characteristics, not only of the volcanoes of Cook's Inlet, but of several others in Alaska. The timber line on the west side of Cook's Inlet has an elevation of about 1000 feet ; above that limit is a belt of alpine flowers, which fade away into the desolate and frequently snow-covered regions about the mountain's summits. 1 W. H. Dall, " Science," Vol. 3, 1894, p. 92. •} ,'/ ..ii:<^ri,'_-^'^'-; f. ;• -»»f«rt«nw.»»««.wwmi»*»««»l» ■ 3 I ! 272 VOLCANOES OF NORTH AMERICA Redoute volcano is similar to its companion just de- scribed, but, so far as I am aware, is unexplored. St. Augustine. — In the southern portion of Cook's Inlet, near the west shore, rises the Island of St. Augus- tine, consisting principally of a single volcanic cone of striking grandeur. (Plate 3, Fig. B.) This volcano in 1880, as stated by Dall,* presented the appearance of a low dome, about 3800 feet high, without a peak. The island on which it stood was nearly circular in outline and about eight miles in diameter. To the northwest, it presented a bluff to the sea, but sloped more gently to the southeast. There are many rocks about it, which were formerly haunted by sea otter. Previous to the great eruption described below, this island was supposed to be of volcanic origin, but there is no authentic record of volcanic disturbances having occurred upon it. In August, 1883, what is described as "smoke" was seen to issue from its summit. On the morning of October 6, the inhabitants of Alexander village, sixty miles to the eastward, heard a heavy report, and saw clouds and flames issuing from the summit of the island. The sky became overcast, and a few hours later there was a shower of pumice dust. About half-past eight o'clock the same day, an earthquake wave, estimated at thirty feet in height, rolled in upon the shore, deluging the houses on the low land and washing the boats and canoes from the beach. Following the first great wave, came others of less height. The dust fell to the depth of several inches, and the darkness was so great that lamps were lighted. At night, flames were seen issuing from the summit of the island, and the snow, which 1 " Science," Vol. 3, 1884, p. 92. VOLCANOES OP THE UNITED STATES 273 previously whitened it, disappeared. After the first dis- turbances were over, it was found that the northern slope of the summit had fallen to the level of the cliffs which form the shore, and the mountain appeared as if split in two in an east and west direction. Two pre- viously quiet volcanoes on the Alaskan peninsula began simultaneously to emit smoke and dust ; and in the ten- fathom passage between Augustine Island and the main- land a new island, approximately seventy-five feet high and a mile and a half in extent, made its appearance. In August, 1895, Dall visited Cook's Inlet, and reports that an excellent harbor for small crafts, which existed on St. Augustine Island before the eruption of 1883, has been converted into a placid lagoon. A slender cloud of steam ascended from the summit of the volcano, which seems to have been built up by eruptions of lapilli and dust since the explosion that rent it asunder. The steam column serves as a barometer for the sea- otter hunters. When it ascends undisturbed by the upper-air currents and spreads out aloft like the well- known " pine tree " of Vesuvius, the natives put to sea in their frail skin boats, or kyaks, confident of two or three days of fine weather.^ Unimak Island. — This is the first or most easterly of the Aleutian islands and is separated from the Alaskan peninsula by a narrow strait, now nearly closed at its northern entrance by sand bars. The island is about sixty miles long in an easterly and westerly direction, and averages twenty miles in width. Its most prominent I ., * An account of the eruption of Mt. Augustine, accompanied by a sketch of the peak after being split in two, is given by Professor George Davidson, in "Science," Vol. 3, 1889, pp. 184-189. Mi t i^ 'I! ■^^ 4 II m 274 VOLCANOES OF NORTH AMERICA topographic features are two volcanic mountains which are among the most interesting and instructive in Alaska. The highest of these, situated near the centre of the island and known as Shishaldin, has gracefully curving sides and rivals in beauty the far-famed sacred mountain of Japan. Its summit is bare of snow, although reported to be from 8000 to 9000 feet high. Since its first dis- covery by Russian navigators, it has been nearly always in a state of mild activity, as shown by the steam ascend- ing from its summit, and occasionally has been the scene of violent explosions. To navigators it is one of the most familiar landmarks on the Alaskan coast. The second volcano, Pogrumnoi, on the western portion of Unimak Island, is said to be between 5000 and 6000 feet high. Little else is known concerning it, however, except that it has frequently been in eruption. As stated by Petroff,' Unimak Island has been and still is the theatre of the most constant volcanic activity in all Alaska. "Whole ridges of mountain peaks have been observed to split open and emit flames, torrents of lava, and clouds of ashes. These manifestations were always accompanied by the most violent earthquakes, tidal waves, and floods, the latter caused by the sudden melting of masses of ice and snow on the mountain tops. The great- est activity on record occurred in 1796, 1824, and 1825, and as late as 1827 burning lava was observed descending from the craters. Oonimak (Unimak) has also from time immemorial been the Aleutians' great storehouse, from which they obtained sulphur and obsidian, the latter being employed in the manufacture of knives, spears, and arrowheads. The Russian missionary, Veniaminof, who 1 Report on Alaska in Tenth Census, 1884, p. 91. VOLCANOES OF THE UNITED STATES •JT5 witnessed one of these eruptions, describes tlie event as follows : " On the 10th of March, 1825, after a prolonged sub- terranean noise, resembling a heavy cannonade, which was plainly heard on the islands of Unalaska, Akoon, and the southern end of the Aliaska peninsula, a low ridge on the northeast end of Unimak opened in five places with violent emissions of flames and great masse.'' of black ashes, covering the country for miles around. The ice and snow on the mountain tops melted and descended in a terrific torrent five to ten miles in width on the east side of the island. Until late in the autumn the sea on that coast was turbid after this eruption. The Shishaldin crater, which up to that time had also emitted flames, continued to smoke only, while about midway between summit and base a new crater was formed, which was still smoking in the year 1831. On the 11th of October, 1826, a small peak in the interior of the island opened under violent explosion of fire and rain of ashes, which covered not only the southern end of Aliaska peninsula, but Sannakh and Ounga and other adjoining islands. Since that time smoke comes out of many places among the loose masses of rocks on the mountain side, and all the streams and ponds in the vicinity are hot enough to emit steam in midsummer." From the graceful outlines of Mt. Shishaldin, shown in the illustration forming Plate 15, Fig. B, reproduced from a photograph taken about ten miles at sea to the north, it appears that the mountain is a lapilli cone built principally of material extruded during mild explosions. Steam was seen at the summit of the mountain in the summer of 1895. So far as known, no one has ever 1 1 1 1 ! , 'I 1! t .1 1 ■ i 1 MJ 1 .<. I ,/ II .(I /I I 1 I' 270 VOLCANOES OF NORTH AMERICA ascended Shislialdin. A study of this splendid volcano would certainly be productive of much valuable information. Bogosloff Island. — In Bering Sea, about forty miles west of the northern extremity of Unalaska Island, and in latitude 53° 58', longitude 168° W., t.iere is an island composed entirely of volcanic rock which has been formed by eruptions within historic times. The island is known to the Russians as loanna Bogoslova (St. John, the theo- logian) and to the natives of the Aleutian islands as Agashagok ; it is now commonly called " Bogosloff." Near the locality where Bogosloff now rises, an isolated rock was long ago known to the natives of the Aleutian islands, and represented on certain Russian charts bearing the date of 1768-69. This rock is mentioned by Captain Cook, who saw it in 1778, and named it Ship Rock. It is stated by DalP that in 1795 the natives on Una- laska noticed what appeared to be a fog in the neighbor- hood of the rock, which did not disappear when the rest of the atmosphere was clear. In the spring of 1796, one of the natives more courageous than his companions visited the locality and returned in terror, saying that the sea all about the rock was boiling, and that the supposed fog was the steam rising from it. The disturbance was accompanied by activity in the craters on Unimak and Unalaska islands. In May, 1796, a considerable mass of material was upheaved and the major part of the present island was formed. Accounts of the appearance of Bogosloff by natives and Russian observers, cited by Dall, Petroff, and others, do not furnish ansAvers to many of the questions that a student of volcanic phenomena would like to ask. 1" Science," Vol. 3, 1884, pp. 89-93. VOLCANOES OF THE UNITED STATES 277 Unsuccessful attempts to land on Bogosloff were made by Dall in 1872, and again in 1873. The island then had a sharp, narrow summit ridge about 850 feet high, cov- ered with inaccessible pinnacles, but there was no appear- ance of a crater. The shores were mostly precipitous, except at the southern end, where the waves and currents had formed a small spit of talus, on which a landing could be made in favorable weather, but the short swell pro- duced a heavy surf. When seen througli a glass, from a distance of four miles, the island appeared of a light purplish-gray color, devoid of vegetation or water, and covered with myriads of birds. In October, 1883, a violent eruption occurred at Bogos- loff, at tlie same time that Mt. St. Augustine, in Cook's Inlet, was active. The island was enveloped in steam and a new crater is reported to have been formed, which has since been more or less active. Great changes in the form of the island also occurred, and near at hand, where a great depth of water was formerly reported, land was elevated to a height of nearly 300 feet. At the time of the eruption just referred to, a dark cloud of dust covered the sky northward of Unalaska Island and hung near the surface of the sea for about half an hour. It excluded the lisj-ht of the sun and was accompanied by a rise of temperature. The cloud then drifted over Unalaska, and dull gray vol- canic dust of extreme lightness fell in considerable abun- dance. During the eruption, Makushin, one of the most recently active volcanoes on Unalaska Island, was quiet, although earthquake shocks were felt. After the erup- tion a new island was discovered near the former one, at a locality where ships had previously sailed in safety; and in September, 1883, was reported to be '' a mass of ■ ■I !■ 1»B*I mmt I I I :! K ( :r: li ii ii I ri r ! I: t 278 VOLCANOES OF NOllTH AMEUICA fire," pn^biibl}' rod-hot rooks, and steam. This new island, situated lialf a nule nortiiwest from "Old IJogoslotT," when first seen was conieal in shape, with an irregular outline, 500 to SCO feet high, and about three-quarters of a mile in diameter. BogoslotV Island was visited by Lieutenant J. C. Cart- well and Surgeon II. W. Yemans of the U. S. Revenue Marine steamer Cortvin, in 1884, and many instructive observations made.^ Approaching the island from the northeast, Cartwell found it to have the appearance of being divided into two parts (Plate IG, Fig. A), the northern portion (New Bog(jslott') being in a state of eruption, and the southern portion (Old Bogoslotf) a much more serrate rock rising almost perpendicularly from the sea, without signs of activity. Between the two and nearer the northern part of the New Bogosloff, a tower-like rock rises with a slight inclination toward the north to a height of eighty-six feet. At a distance, the central rock might easily be mis- taken for a sail upon the horizon, and for this reason is called Ship Rock or Sail Rock. A nearer approach dis- closes the fact that the two elevations are connected by a low, flat beach, free from rocks, which affords an excellent landing-place for small boats. The narrow isthmus connecting the two prominent por- tions of the island is composed of a mixture of fine black sand and small oolitic stones. This isthmus is evidently of tlio nature of a sand bar formed by the waves, of mate- rial washed from the higher portion of the island; pos- ' Report of the Cruise of the Revenue Marine Steamer Corwin in the Arctic Ocean in the Year 1884, by Captain M. A. Healy, U.S.R.M., Com- mander, Washington, 1889, pp. 39-44. Wk. VOLCANOES OF THE UNITED STATES 279 Hibly a sllglit elevjition is liuru rt'conled ; tlio nuwur portiun of the isljind IxMiig at first discoiinoctL'd, as was reportud by some (observers. As related byCartwell: "The sides of New IJogoslolf rise with a gentle slope to the crater. The ascent at first appears easy, but a thin layer of ashes, formed int(j a crust by the action of rain and moisture, is not strong enough to sustain a man's weight. At every step my feet cruslu'd through the outer covering and 1 sank at first ankle-deep and later on knee-decii) into a soft, almost impali)able dust which arose in clouds and nearly sutt'ocated me. As the summit was reached, the heat of the ashes became almost unbearable, and I was forced to continue the ascent by picking my way over rocks whoso surfaces, being exposed to the air, were somewhat cooled and afforded a more secure foothold. " On all sides of the cone there are openings through which steam escaped with more or less energy. I observed from some vents the steam was emitted at regu- lar intervals, while from others it issued with no per- ceptible intermission. Around each vent there was a thick deposit of sulphur, which gave off suffocating vapors." No appearance of lava streams or of cinders was noted. Small quantities of rock froth, consisting of unfused particles in a semi-fused mass, were seen, but during its extrusion the rocks do not appear to have been sufficiently heated to cause true fusion. A walk of a third of a mile along the beach mentioned above brings one to Old Bogosloff, where the beach abruptly terminates against rugged rocks, which rise almost perpendicularly to a height of 325 feet. Surgeon Yemans states that the origin of New Bogosloff was first ■4 I" ■ Iff ■_■ v'V^ 'w 4 :ii :^! i, lili hi! iili : 280 VOLCANOES OF NOUTII AMERICA made known by Captain Anderson of the .schooner Matthew Turner, who waw it on September 27, 1883, and reported that great volumes of steam and ashes were erupted from tiie summit and also from numerous fissures on the sides and base. At night bright rellections from the highly heated interior were distinctly visible. Samples of rock and dust collected by the gentlemen whose reports have just been cited were examined by G. P. Merrill of the United States National Museum, and ascertained to be hornblende andesite. The dust was found to be identical with dust that fell at Unalaska, sixty miles distant, at the time of the eruption. The rocks are considered as ejected fragments of some under- lying strata and not recent lava flows, thus confirming Cartwell's observation in reference to the absence of molten lava. An account of the ^ineralogical and chemical composition of the materia ^x'ming Bogosloff may be found in " Science," Vol. 4, 1884, p. 524. Although not personally familiar with Bogosloff, I venture to suggest from what I have seen in connection with other volcanoes, that the formation of the island was due to the outwelling of viscous lava, which hardened at the surface so as to resemble the rough, scoriaceous surface so common on lava flows. The lava, being quickly cooled, did not flow as a stream, but as in the case of some of the Mono craters previously described, rose in rugged, scoriaceous masses, without much explosive vio- lence. Nothing resembling a crater ring of lapilli and dust is reported as surrounding the elevated crags of lava. Dall remarks that other islands similar to Bogosloff in origin are known in the same general region.* Mention 1 "Science," Vol. 3, 1884, p. 92. VOLLAXOKS ol' NOKIII AMKliK' A. ri.ATK KJ. — -?fp ■*> J Fid. A. IJoju'osIofT. Beriiii; Si-ii, ISHI. ( Fli(it(>;;ia|ili hy T. S. Kisli ('(imniissioii.) Fig. U. New Bogosloff, Bering Sea, 1884. (Photograph by I'. S. Fish Commission.) ■."v-,,:"T-: .^^iiiLjwu^.j.'mww 11 1 ij 1^1 1 ■ '' 1 1 \ 1 1 VOLCANOES OF THE UNITED STATES 281 is made of Koniugi and Kasdtochi in the western Aleutian chain, and of Pinnacle Island near St. Matthew's Island, Bering Sea. The last differs from Bogosloff in having the crest deeply channelled. It is reported that light has been seen in the fissures of Pinnacle Island "within the last few years by navigators passing in the night," though there is no record of steam having been noted. Unalaska Island. — The Island of Unalaska is next to the largest and in the development of Alaska the most important of the Aleutian chain. It is about 120 miles long by 40 miles wide, and has a deeply indented shore line. Its borders are bold and its surface exceedingly rugged. Dominating the wild, treeless landscape to be seen while sailing along its shores, and as observed by the writer from a steep-pointed summit left by erosion, near its northeast extremity, stands Mt. Makushin, with an elevation of 4000 or 5000 feet. This mountain is of volcanic origin, although it has not been in active erup- tion, so far as can be learned from Russian records or from the traditions of the natives, within several genera- tions. Steam still issues at intervals from its summit, and earthquakes and subterranean noises which seem to proceed from the mountain indicate that it should be considered a dormant rather than extinct volcano. Petroff states in his report in the Tenth Census, page 92, that Russian naval officers who visited Unalaska at long intervals in the early part of this century, assert that many of the points and ridges on Makushin were observed to have changed in outline owing to vol- canic action between their several visits. North of Makushin and in plain view from the hills about Iliuliuk, the village usually visited by vessels bound f 282 VOLCANOES OF NORTH AMERICA I i for Bering Sea and the Arctic, rises another conical vol- canic mountain about 3000 feet high. Tliis volcano has long been extinct and its sides are scored with erosion channels. Central and Western Aleutian Islands. — Information concerning the volcanoes of the Aleutian islands is for the most part so meagre and of such a general nature that to attempt to compile all of it would result in little more than a catalogue of names, with a few dates at which eruptions have been seen. Such compilations have al- ready been made by Grewingk, Dall, and Petroff, as pre- viously stated. As the reports of these explorers are in many libraries, it is unnecessary to republish the cata- logue of volcanoes they contain. On many of the islands there are volcanic mountains with craters, and deposits of lava, lapilli, dust, obsidian, etc., are abundant. Hot springs occur at many localities. The general appearance of these volcanoes as seen from the sea is illustrated by the accompanying photograph of Mt. Cleveland on the Islands of the Four Mountains and of a similar cone known as Pavaloff volcano on the Alaskan peninsula. These pictures, together with the illustration of Shishaldin, will serve to give some idea of the topography of the volcanic belt of southwestern Alaska. Summary. — Meagre as is the accurate information con- cerning the large number of volcanoes in southern Alaska and on the Aleutian islands, it is sufficient to show that a wonderfully interesting region there awaits careful study. The most instructive facts now in hand relate to the dis- tribution of the volcanic vents in a well-defined belt. This, taken in connection with the topography of the :.'*iIj^^\'L^^ii:.S:ixt-ii': VOLCANOES OF THE UNITED STATES 283 region, and the records of recent upheavals as shown by elevated beach line,;, indicates that profound fractures have there occurred, accompanied by faulting and the elevation of plateaus, like that bordering Cook's Inlet on the west. The geological structure in much of southwestern Alaska, so far as can be judged, resembles that of the Great Basin ; the main geographic features being due to the upheaval and tilting of great blocks of the earth's crust. The association of numerous active volcanoes with a narrow belt of fractures is significant, and, as in Central America, suggests that forces tending to break the earth's crust when concentrated along narrow belts are able to keep open communications with the earth's highly heated in- terior, much more effectually than when the disturbances affect a broader region, as in that portion of the Cordilleras which crosses the United States. In closing this sketch of the volcanoes of North America, I feel that the impression obtained by the reader will be that a vast field of great interest to the student of volcanic phenomena has been pointed out, but that our information concerning it is meagre and unsatisfactory. If, however, what I have written serves to stimulate inquiry and en- courage fresh exploration and study, I shall feel more than repaid for the labor expended in compiling this book. 'Ill' :\ t hi li ^ } ~Ti CHAPTER VI DEPOSITS OF VOLCANO DUST Among the important contributions of volcanic origin, made to the surface of the land over large proportions of North America, are certain deposits of fine, dust-like material, which was blown out of volcanoes m widely separated regions and distributed over great areas by the wind. Several references to these highly interesting accumulations have been made in preceding chapters, but at the risk of some repetition, a brief summary of what is known concerning them it is believed will be instructive. Distribution. — Travellers in Central America and Mex- ico frequently refer to the deep, rich soils of that region, which consist largely of what are usually termed vol- canic ashes. Over extensive areas the soil is com- posed of disintegrated volcanic rock, which grades on one hand into fragments of pumice and lapilli, and on the other hand passes into fine volcanic dust. Much of this material is known to have resulted from the ex- plosive eruptions of Conseguina, Izalco, JoruUo, and other volcanoes that have been in eruption since the Spanish conquest; but the greater part of the soil-making vol- canic debris came from prehistoric eruptions. Under the influence of the moist, warm climate, preva- lent in the greater part of Central America and Mexico, 284 .....^.(r^^.-. DEPOSITS Oi^ VOLCANO DUST 285 the fine volcanic material strewn over the surface rap- idly decomposes, and becomes available as plant food. An efficient method of natural fertilization and soil- renewal is thus illustrated. In the Sierra Nevada, and over large portions of the Great Basin, deposits of volcanic dust many feet in thick- ness are frequently met with.* These occur both on the surface and especially at the mouths of gorges in the uplands, where the dust has been washed down and accumulated in alluvial cones, and interbedded with the sediments of Pleistocene lakes. Evidently the volcanic eruptions which furnished the dust occurred both in Pleistocene and Recent times. As explained in a pre- vious chapter, these deposits occur in great abundance about the Mono craters, and have been traced with con- siderable certainty to a distance of fully 200 miles north- ward from them. Near the Mono craters, these deposits are coarse and are mingled with gravel-like lapilli, but become finer and finer, and less and less abundant, with increasing distance from their source. The similarity of the volcano dust occurring at a distance — as in northern Nevada — to that found abundantly in Mono valley, is not confined to physical properties, but embraces chemical composition as well. Analysis of volcanic dust collected in Truckee canyon, near Pyramid Lake, Nevada, and of the pumiceous rhyolite forming a large part of the Mono craters, shows an almost identical composition. The proof is then almost conclusive that the widely distributed dust bi ^ I. C. Russell, " Quaternary History of Mono Valley, California," United States Geological Survey, 8th Annual Report, 1886-87, pp. 386, 387. " Lake Lahontan," United States Geological Survey, Monograph, Vol. XI, 1885, pp. 146-149. _ ...tppmrn 1 t ,'. 1 1 \ t 1 1 1 1 i : 1 , 1 » , MM ' III itli 286 VOLCANOES OF NORTH AMERICA came from the same source as the lava forming the vol- canic mountains in Mono valley. Dust-like deposits of volcanic origin are of common occurrence in Utah, especially in the vicinity of Salt Lake City, and attain a thickness in several instances of from thirty to fifty feet or more. Some of these deposits are interbedded with lacustral sediments of Tertiary age ; but others are probably much more recent, although but little definite information concerning them is available. Widely spread deposits of volcanic dust occur over great areas in Montana, South Dakota, Nebraska, and Kansas. Some of these beds are of Tertiary age, others occur beneath fine, clay-like material termed loess, of Pleistocene age, w^hile still others occupy depressions in the present surface, or fill hollows formerly occupied by lakes, and are clearly post-glacial. The deposits of volcanic dust in Nebraska, as stated by Professor E. H. Barbour,^ have been discovered in twenty counties which are so situated as to show that the entire strata were covered by the dust showers. These deposits were formed after the land had its present topography, and are coarsest and in greatest abundance, being some- times fifty feet thick, in the southwestern portion of the state, and become gradually thinner and finer when traced eastward. This arrangement indicates that the volcano from which the material was deri ed is situ- ated to the southwestward of the western part state. * Nebraska Academy of Science, Vol. 5, 1894-9.5, pp. 12-17. In this essay, illustrations showing the appearance of the dust when examined with the aid of the microscope are given, together with drawings of the flakes composing ground pumice, for comparison. DEPOSITS OF VOLCANO DUST 287 vol- of As to color and texture, some of the Nebraska deposits are as pure and fine as the best ground pumice of com- merce. From this nearly pure-white material there are all gradations to that which is discolored with iron and organic matter, and so coarse and mingled with so much silt that one cannot decide whether the dust or the matter mingled with it predominates. Thick deposits of volcanic dust similar in nearly every particular to that of California and Nevada, and in the region referred to east of the Rocky Mountains, occur at numerous localities in Oregon and Washington. Many of these deposits contain the leaves of Tertiary plants, or are associated with laciistral sediments and lava flows in such a manner as to show that they are of Tertiary age. In some instances, however, accumulations of the same kind of material are found on the surface, and in such relation to the present topography as to demonstrate their recent origin. At a late date, but not deter- minable in years, a light shower of fine, pure-white vol- canic dust fell on an area of fully 10,000 square miles in southeastern Washington and adjacent states. This deposit has been so commingled with the soil that its presence is seldom recognizable, except at the mouths of ravines and gulches in the sides of the valleys, where it has been concentrated by small streams so as to form alluvial cones. In many such localitier a depth of from ten to twenty feet or more of fine, white, highly siliceous dust may be seen. This last light shower of dust, although of slight importance in • comparison with the deposits many feet in thickness of older date, in the same region, yet in the aggregate added many thousands of tons of fertilizing material to the region over which it I! 'i H 'V3 :| ■ -"«••»»>•* !i5H i »■■' 'I : I !»' li '.I 1 1 .Will III nil I > .' I 1- 288 VOLCANOES OF NORTH AMERICA was spread. The volcanoes' from which the abundant volcanic dust deposits of the Pacific Northwest were de- rived are unknown, but were probably in the Cascade region. The more recent dust showers may reasonably be ascribed to the volcanoes of which Baker, Rainier, and Shasta are representatives. In Alaska and adjacent portions of Canada, still other extensive deposits of volcanic dust of recent date are known. The writer, while journeying up the Yukon River in 1889,^ observed above the mouth of Pelly River, a conspicuous white band from eight to twelve inches thick, in the upper portions of the river terraces, which was traced for fully 200 miles. This deposit of remark- ably pure volcanic dust had previously been noted in adja- cent regions and was more fully examined by Hayes in 1881.'^ These various observations show that it occupies an area of fully 52,280 square miles, and varies in thick- ness from a few inches on its northeast border, to between 75 and 100 feet near its southwest margin. Its volume has been computed by Hayes to be in the neighborhood of 165 cubic miles. The volcano from which this vast erup- tion of fine dust was derived is as yet unknown, but from its distribution, and its increase both in thickness and in coarseness toward the southwest, the point of eruption is judged to be some seventy-five miles northwest of Mt. St. Elias. This Alaskan deposit is pure white, except when impu- rities are present, and indisti.iguishable, at least in its *I. C. Russell, "Notes on the Surface Geology of Alaska," in Geologi- cal Society of America, Bulletin, Vol. I, 1890, pp. 145, 146. " C. W. Hayes, " An Expedition through the Yukon District," in "Natio.ial Geographic Magazine" (Washington, D.C.), Vol. 4, 1892, pp. 146-150. DEPOSITS OF VOLCANO DUST 280 physical properties, from the similar material found so abundantly in California, Oregon, and Washington. In Alaska, the dust rests in part on moraines which have been abandoned in recent times by the still retreating glaciers, and occurs in post-glacial terraces along the Yukon, and is therefore of recent origin. The great abundance of volcanic dust in the Cordilleran region, its wide distribution, and its occurrence in numer- ous instances at many horizons in the same vertical sec- tion, is evidence that vast areas in western North America have been shrouded in darkness at many separate periods, and have time and again witnessed horrors like those which overwhelmed Pompeii and Herculaneum. Disas- ters similar to those accompanying the eruptions of Con- seguina and Krakatoa occurred at intervals throughout the Tertiary and Recent history of fully one-half of North America. Events of a like tragic character are also recorded by pre-Carboniferous deposits of volcanic dust, now consolidated into hard rock, in the Appalachian Mountains, near Boston, and on the shores of Lake Superior.^ The volcanic dust of the Pacific states sometimes con- tains the bones of mammals and is frequently charged with quantities of leaves, showing that some of the tem- pests generated by volcanic agencies were disastrous to animal and plant life. These and related disturbances in environment probably had much to do with the modifi- cation and extinction especially of the higher mai "aalian species. Physical and Chemical Properties. — The leading physi- * N. H. Winchell and U. S. Grant, " Volcanic Ash from the North Shore of Lake Superior," in "The American Geologist," Vol. 17, 1896, pp. 211-213. .. > \ ILill W MW 290 VOLCANOES OF NORTH AMERICA cal characteristics of the volcanic dust, referred to above, are its whiteness, unless adulterated with other sub- stances, and the angular character of the flakes of glass of which it is composed. The individual flakes are usu- ally too small to be seen by the unaided eye, and in nearly all respects closely resemble powdered pumice. They may be almost precisely duplicated by grinding ordinary glass, or common obsidian, or pumice, in a mortar. When examined under a microscope, the dust /^ i^ T=K. i t'l ^ A ^:=^ -^ ijf <^ >^ ^s^^=:::^ N7 <^ V ^ A t^ ^^Q-" fci 1. Volcanic dust which fell in Norway, March 29 and .TO, IST.'i. 2. Volcanic dust emptied from Krakatoa, August 27, 1883. 3. Volcanic dust from the Truckee River, Nevada. Quaternary. 4. Volcanic dust from Brakleast Hill in Saugus, Massachusetts. Pre-Carboniferous. Fig. 11. Volcanic dust. (J. S. Diller.) is found to consist of angular flakes and shreds of glass, in which irregular cavities are frequently detectable. There is usually an absence of crystalline fragments, but this is not always the case. The appearance of a sample of volcanic dust from Truckee canyon near Pyramid Lake, Nevada, which is representative of a large number of similar deposits between southern California and Alaska, when examined under a microscope, is shown in the above figure, |i' above, ir sub- f gliiss re iisu- xnd in niuiice. finding i, in a le dust O*. V^ boniferous. f glass, ectable. yments, st from hich is deposits lamined figure, DEPOSITS OF VOLCANO DUST 201 together witli drawings of similar material enii)t('d by existing volcanoes, and also an ancient example of like origin but now ccmsolidated into a bard rock, from near Boston. This figure is borrowed from an article by J. S. Diller, on volcanic sand which fell at Unalaski, on October 20, 1883.' In this instructive essa}-, much addi- tional information concerning the nature and origin of the deposits under discussion may be found. One of the most striking facts in connection with tiie widely distributed deposits of volcanic dust enumerated above, is their marked similarity in both physical and chemical characteristics. At almost all of the hundreds of localities examined by the writer between Mono valley and the Yukon, the material is a fine, white, highly sili- ceous powder, which closely resembles pure infusorial earth. The only exceptions to be noted are where the deposits are impure on account usually of the presence of silt and sand ; this occurs especially when the deposits are stratified, showing that in part the material compos- ing them was washed into lakes or other water bodies, and when the dust is mingled with larger fragments of a similar origin, and grades into volcanic sand and lapilli. Additional facts concerning what geologists term jjyrodastics, that is rock material reduced to fragments through the agency of heat, may be found in many text- books of lithology. Although but few quantitative chemical analyses of volcanic dust deposits here considered are available, yet it is believed, from many qualitative examinations, that the two complete analyses given below represent very nearly their average composition. »" Science," Vol. 3, 1884, pp. 651-654. F 292 VOLCANOES OP NOttTII AMEUICA ANALYSES OF VOLCANIC DUST !l if I t CONBTITUKNTH. No.l. No. 2. Silica (SiOa) . . . . 71.15 08.01 Aliiiiiiiiii ( AI^O.,) and iron (1 •ejOs) 15.1)') 0.12 Liiiio (t'uO) 0.H5 3.44 Magnesia (Mk<>) 0.41 — jMangani'se (MnO) . trace — I'otash (K./)) . HM o.:jo Soda (Na.O) . 4.04 3.00 Organic matter — 8.75 Sulpliuric acid (SO.,) — 8.88 100.57 00.55 w: No. 1. From Truckec canyon, Nevada; analyHi.s by T. M. Cliatard; in U. S. Geological Siirvoy, MonograpJi, Vol. 11, p. 147. No. 2. From Nebraska; analysis by 11. II. Nicholson; in Nebraska Academy of Science, Vol. 5, 1804-05, p. 13. The sample from Nebraska is evidently less pure than that from Nevada, as it contains organic matter and prob- ably also sulphate of lime, which have been added to the material that fell as dust. Three analyses of volcanic dust probably of Tertiary age, from Montana and Idaho, published by G. P. Merrill/ show from 65.56 to 68.12 per cent of silica. The marked feature in the composition of the dust is the high percentage of silica. Evidently the dust owes its origin to the disintegration of acid lava. So far as my own observations extend and so far, I believe, as has been reported by others, no deposits of volcanic dust of a basic character have been discovered in North America. ■il 1 "Note on the Composition of Certain 'Pliocene Sandstones' from Montana and Idaho," in "American Journal of Science," Vol. 32, 1886, pp. 199-204. DEPOSITS OF VOLCANO DUST 208 0.30 3.09 8.75 8.88 The richness of volcanic dust in silica has hctMi noted especially by Diller,* who states that in general volcanic sand (fine lapilli) is composed chielly of crystalline frag- ments, and contains a lower percentage of silica than the lava to which it belongs ; while volcanic dust contains more silica than the lava effused from the volcano from which it was derived. In explanation of these interesting facts, the author just cited states that "The difference in chemical composition between volcanic sand or dust, and the lava to which it belongs, appears to be directly prc^por- tionate to the amount of crystallization which had taken place in the magma before its effusion. It is well known that crystals are frequently, and sometimes abundantly, developed in a magma; so that, before its extrusion, the magma may be regarded as made up of a crystalline, solid portion, and an amorphous, more or less fluid i)ortion. These are generally thoroughly intermingled, but occasion- ally they are arranged, as in obsidian, in alternating bands ; and they differ from each other in several important par- ticulars, besides those already mentioned. The earliest products of crystallization are basic minerals, such as the ores of iron, hornblende, and mica ; and as the process continues, the amorphous portion of the magma becomes more and more siliceous. On this account, the crystalline portion of the magma does not contain as high a percent- age of silica as that which is amorphous. In the process of crystallization the gases absorbed in the magma are rejected from the crystallizing substances, and accumulate, under enormous tension, in the portion which is amor- phous. In this manner the non-crystalline portion of the magma becomes stored with explosive compounds, 1 J. S. Diller, " Science," Vol. 3, 1884, pp. 053, 051. i. B^r»^s^5^5=r7!= - •■•* ti'^mtf'^tftfm ^f 294 VOLCANOES OF NORTH AMERICA 'I i 111! in -i under such stress, that when the pressure is relieved, they may blow it to line, siliceous glass-dust; while the crystalline, solid, basic portion of the magma, pulver- ized rather by external than internal forces, is ' iduced to sand." Among the illustrations of the fact that volcanic dust is frequently richer in silica than the parent lava, the com- position of the material discharged by Krakatoa, in 1883, is cited. The dust resulting from that eruption, and widely distributed over the earth, has been found to contain 65.04 per cent of silica ; v/hile the lava effused at the same time contains but 62 per cent of silica. The abundant occurrence of acid volcanic dust, and the fact that basic material of a similar physical character has not been found in the deposits under consideration, is apparently not fully explained, however, by the hypothesis just quoted. In addition to the changes produced in a magma by fractional crystallization, it may bo suggested that the chemical composition of the magmas as a whole, from which the dust was derived, plays an important part. Acid magmas, as stated in a previous chapter, are of different fusibility, and generally form viscous fluids ; while basic magmas are more easily'' fused and form more perfect fluids. The viscous magmas, when expanded by occluded steam and gases, become brittle on the loss of a small amount of heat, and are in a condition to be shattered ; wh\le the more fluid magmas allow the occluded steam and gases to escape without violent explo- sions. This suggestion is in harmony with the well-known fact that most pumice is rich in silica. While eruptions of basic magmas may form large quan- tities of lapilli, and yield dust particles by the attrition DEPOSITS OF VOLCANO DUST 295 of projected fragments, the proportion of dust due to the explosion of occluded steam would be comparatively small ; on the other hand, siliceous and usually viscous magmas would be shattered by the explosion of the steam con- tained in them, and give origin to an al)undance of dust- like particles. The presence, therefore, of vast accumula- tions of siliceous volcanic dust, and the absence of basic material of similar nature in the Cordilloran region, is rather to be accounted for by the fact that volcanoes effusing acid lava manufacture vastly more dust particles than those from which only basic lavas are extruded. The fractional crystallization that takes place in cooling magmas cited by Diller, while no doubt an important factor favoring the production of acid volcanic dust, seems too delicate an adjustment to alone account for the vast abundance of acid volcanic dust and the ab- sence of basic material of like character over a large portion of North America. In Oregon and Washington, for example, the igneous rocks that occur in greatest abundance are of the basic type, while all of the dust deposits known are rich in silica. Rather tb m expect that a basic magma like that producing basalt could, Ijy fractional crystallization, give origin to highly acid dust, it seems more rational to assume that the Ijasic lavas came from different eruptions than the volcanic dusts so abundantly associated with them. Economic Importance. — Volcanic dust is used as an abrasive principally in the form of polishing powder and as an ingredient in friction soap. It is serviceable for most if not all of the uses for which ground pumice and diatomaceous earth are employed. Experiments have shown that it may be used with satisfactory results in ■MMHMMBid»i»ii«IH«n«feli P0> Mt fj K (I 'II I 'l,i II h uil\ %\ I! ii ' ! i .:i ! ! 296 VOLCANOES OF NOliTH AMERICA connection with paint as a substitute for sand in cer- tain processes of painting, particularly when the surface coated is exposed to the weather. Other uses for this abundant and remarkably clear, white, siliceous powder will no doubt be found. CHAPTER VII THEORETICAL CONSIDERATIONS li'> All modern theories that have been advanced to ac- count for volcanic phenomena rest on still other and more general theories in reference not only to the condi- tion of the interior of the earth, but to the origin of the earth itself. The meteoric hypothesis of Lockyer, which may be con- sidered as a modification of the earlier nebular hypothesis of Laplace, more nearly satisfies the facts observed in reference to the present condition and to the origin of the earth, than any other explanation that has been advanced, but cannot be considered as entirely satisfactory. With- out attempting to discuss the profound problems referred to, we will assume, for the present, that the earth reached its present condition after a long period of cooling from a molten condition, during which a cool and solid crust was formed about a still highly heated interior. Internal Heat of the Earth. — As is well known, there are abundant observations to show that diurnal changes of temperature do not affect the earth below a depth of about three feet ; while seasonal changes of temperature do not occur below an average depth of about forty feet. Any temperatures that the earth may have below this depth, therefore, cannot be due to the radiant energy of the sun. Below the depth in the earth to which the in- fluences of seasonal changes are felt, there is, as shown by 297 II I ! 298 VOLCANOES OF NORTH AMEUICA 1 ; I ! •15 obseivation, a zone of invariable temperature, below which the temperature increases in general at the rate of one degree Fahrenlieit, for each fifty or sixty feet of descent. At this rate of increase, a temperature of 212° would be reached at a depth of about 8000 feet. At a depth of thirty miles the temperature would be such that all known substances would melt under ordinary atmospheric pressure. The measurements on which these well-known conclusions are based do not extend below a depth of approximately one mile, but are sustained, at least in a qualitative way, by the phenomena observed in volcanoes and hot springs. The accepted conclusion is tluat the interior of the earth below a depth of a very few thousand feet is intensely hot. Computations made by Tate, based on the observed rate of increase of temperature towards the centre of the earth, and the rate at which rocks conduct heat, have shown that the internal heat of the earth is being carried away and dissipated in space at the rate of 250 units of heat per annum per square foot of the earth's surface ; the unit of heat used being the amount of heat necessary to raise the temperature of one pound of water one degree Fahrenheit. The computed annual loss of heat from each square foot of the earth's surface is sufficient to warm one and one -fourth pounds of water from the freezing to the boiling point. If we accept the conclusion of Laplace, Lockyer, and others, — that the earth was formerly in a molten condition, — it fol- lows that the rate at which the earth has been losing heat was formerly greater than now, and that it will continue to decrease in the future. Another inevitable conclusion is that this loss of heat has been accompanied i'. i f 1 ■lii kV f THEOllETICxVL CONSIDKllATIONS 209 by contraction. The earth is smaller than formerly and will continue to decrease in size. Condition of the Earth's Interior. — The observed in- crease in temperature with depth in the earth naturally lead to the supposition that the interior is in a molten condition ; but when the influence of pressure on the fusing point of rocks was considered, it became ques- tionable whether any portion of the interior could exist in a liquid condition. Astronomers have shown conclusively, as it appears, that the earth behaves, in reference to the attraction of the sun and moon, like a rigid sphere ; the conclusion being that the earth is as rigid as a sphere of steel of the same dimensions. Geological observations have proven conclusively that the earth's surface is continually in motion. Portions of the surface are undergoing elevation, while other por- tions are being depressed. The proof is abundant, also, that similar movements have been in progress since the dawn of geological history. The differential mo^ eraents of adjacent areas in numerous instances are measured by tens of thousands of feet. These apparently opposite conclusions reached by as- tronomers and geologists may be harmonized on the hypothesis that the interior of the earth, although highly heated, is solid by reason of the pressure to which the rocks composing it are subjected, but that they would become plastic or even highly fluid if the pressure was sufficiently relieved. This condition of the earth's in- terior is expressed by the term potentlalhj plastic; that is, the material of which it is composed is solid by rea- son of the pressure under which it exists, but would ■l:| n - i I .iw^pp '^ • * f 1 I i I) ,^ ( ' t s i !i II. I r^\ I I I i V i i t; ! i 1' t 1 1 » 1 300 VOLCANOES OP NORTH AMEUICA become plastic, by reason of its heated condition, if the pressure were relieved. In brief, the conception of the condition of the earth that is in harmony with the con- clusions reached by both astronomers and geologists is, that it consists of a comparatively thin, rigid shell, termed the earth's crust, enclosing a highly heated and solid, but potentially plastic, sphere, — the passage from one to the other being gradual. The inner sphere sus- tains the pressure of the outer shell, or, more accurately, pressure increases Avith depth ; but if pressure is suffi- ciently relieved on a portion of the heated interior, it will at once become plastic or liquid, and in a condition to flow under moderate pressure. Changes on the earth's surface — such as the removal of material from one locality to another, through the action of rivers, etc. — lead to changes in the pressure of the crust on the potentially plastic interior, and tend to change its shape. Contraction, accompanying loss of heat, decreases the size of the inner sphere, and the rigid crust has to adjust itself to the shrinking mass within ; this it does by folding or bending, and by fractures and the overthrusting or underthrusting of the rocks on the sides of the break. Accompanying these changes are both regional and local elevations and depressions of the earth's surface. A fracture in the earth's crust, if it reached from the surface to the highly heated interior, would be equiva- lent to a relief of pressure. The highly heated and potentially plastic rocks in the vicinity of such a fract- ure would at once become plastic or even highly fluid, and be forced into the break by the pressure of adjacent rocks. When the pressure was sufficient to force the THEOUETICAL CONSIDKUATIONS 301 molten material to the surface, volcanic plicnomona would ensue. Before testing this hypothesis, other facts concerning the earth's crust should be considered. Intrusive Rocks. — Observations in many regions have shown, as stated in tlie first chapter of this book, that fractures have occurred in the earth's crust at many different geological periods, and been injected with molten rock which has been forced into the fissures from below. Fissures filled in this way are known as dikes. They vary in width from a few inclies or even a fraction of an inch to hundreds of feet, and are fre- quently scores of miles in lengtli. They may appear as vertical or variously inclined sheets cutting across the bedding of stratified or other rocks. In many instances, molten rock has been forced between stratified rocks, and, on cooling, formed sheets having the same bedded arrangement as the enclosing layer. Layers of crystal- line rock orisjinatinoj in this manner are termed intruded sheets, in distinction from surface overflows, or extruded sheets. Under certain conditions not well understood, molten rock forced into the earth's crust from below, instead of breaking through the strata or spreading out between them, causes them to rise, and cisterns of molten material are formed beneath them ; a series of uplifts are thus formed, which are known as plutonic plugs, laccolites, and subtuberant mountains.^ These various classes of igneous intrusions occur in the earth's crust, sometimes at great depths, as is shown hy the amount 1 1. C. Russell, " Igneous Intrusions in the Neighborhood of the Black Hills, Dakota," "Journal of Geology," Vol. 4, pp. 177-194. "On the Nature of Igneous Intrusions," "Journal of Geology," Vol. 4, 1896, pp. 23-43. " Igneous Intrusions and Volcanoes," " Popular Science Monthly," December, 1896. :' lil ■1 li !l I 'mmwm \ i \ \ I N'' .1, \ 1 , ]•■'■ 1 i 1 302 VOLCANOES OF NOIITH AMERICA of rock oroJcd away so as to expose them at the surface, and must have been forced m against an enormous pres- sure. The force or pressure which caused these intru- sions is so vast in many instances that one fails to compreliend its magnitude. As described in the papers just referred to, great mountain ranges in the central part of North America — like the Black Hills of Dakota, Big Horn Mountain, Wyoming, and the eastern range of the Rockies in Colorado — belong to a class of uplifts designated as subtuberant mountains, and are believed to owe their origin to great reservoirs of molten rock forced into the earth's crust. Relation between Igneous Intrusions and Volcanoes. — As we have just seen, dikes result from the filling of fis- sures with molten rock, which in m.ost instances is forced in from below ; the best explanation that has been given of the origin of intruded sheets, plutonic plugs, laccolite, and subtuberant mountains, is that intruded rock was forced upward through fissures in the deeper part of the earth's crust and expanded in various ways in its more superficial portions, and especially in regions of horizontally stratified beds. The primary conditions leading to the origin of these various forms of intrusions, are : (1) deeply seated reservoirs of plastic or potentially plastic rock in the earth's crust or below" it, and under great pressure ; (2) fissures formed in the crust and opening into the deeply seated reservoirs. Under these conditions the highly heated material below the surface, when fissures were formed in the crust, would become plastic, or perhaps highly fluid, and being under great lateral pressure, would be forced upward into the fissures. The behavior of the material injected into )i THEORETICAL CONSIDEIIATIONS 303 the earth's cnist in this manner woukl vary according to the character of tlie fissures, the deptli to which they reached; tlie structure of the rocks through which tlie magmas rose, whether stratified or massive, and if strati- fied, whetlier horizontal or inclined, and if water-charged or not ; the nature of the magmas themselves, whether easily fusible or refractory, etc. The influence of these various conditions has been considered in the essays just referred to. Volcanoes in many instances are known to be located on fissures in the earth's crust. The dissection of vol- canic mountains by erosion has shown, in many instances, that the conduits through which the lava rose were fract- ures, which, being filled with molten rock, formed dikes as the magma cooled. It is evident, then, that igneous intrusions and volca- noes are phases of the same process. Fissures originat- ing in the lower portions of the earth's crust, but failing to reach the surface, would, on being filled with molten rock, be transformed into dikes, and in regions where great thicknesses of horizontally stratified beds occur, might lead to intruded sheets, laccolites, etc. If the fis- sures extended from the highly heated interior to the sur- face, — or if less extensive fissures are formed in the lower portion of the crust, and the force of the injected magma, acting like a wedge, prolong them to the surface, — molten rock would be poured out and a surface overflow occur, that is, a volcano would be formed. A single fissure might thus lead to the origin of intrusions of various forms, and also to volcanic eruptions of various kinds, according to the modifying conditions. The primary conditions leading to surface discharges of molten rock M;^ ii I t ) in •"HP -.. -, I .1 I' V. i ii ' :i- 'H "i: I' I * ''' i IM 4 h:: , li 1 i' 1 1 r' i: : 'fi 'i( J 1 ■ ?' '\ ' '1 i il i JiJ 804 VOLCANOES OP NORTH AMEIUCA or extrusions, arc the same as those which give origin to suljterranean injections or intrusions. Source of the Steam of Volcanoes. — The most striking feature of volcanic eruptions and one, so far as now known, always present, is the abundant escape of steam. Steam frequently escapes in vast quantities and even with explo- sive violence when no molten rock is visible. The resem- l)lance of an eruption of a mild cliaracter, as when a volcano is in the Strombolian stage, to the boiling of mush in a tall vessel through the actiov. of heat applied at the bottom, illustrates the action that is witnessed in many volcanoes. In this explanation and in nio.«t others that have been suggested, steam is appealed to as the main and essential force which causes the molten lava to rise in a vo! mic conduit. That steam given off by vol- canoes is not the cause of the rise of lava in fissures, however, is indicated by the fact that rocks forming dikes are not vesicular, but, as every geologist knows, are among the most compact and solid of igneous rocks. It has been shown by Van Hise, apparently on sound principles and correct reasoning, that what may be termed appreciable cavities cannot exist in the earth's crust at a depth in excess of about 30,000 feet. This and other considerations lead to the conclusion that the portion of the earth that is water-charged is the outer layer of the crust. Beneath the sea and land alike, except perhaps in desert regions, the rocks are filled with water, prob- ably to the depth of several thousand feet. In deep mines and wells, with few exceptions, the rocks are moist and usually abundantly water-charged. Molten magmas, rising through fissures and approach- ing the earth's surface, would invade a water-charged THKOUETICAL CON'SIDEIlATIONS nor) :oacli- zone. The molten rock, on coming in contact Avith water in the rock.s, would vaporize it, or even cause a dissocia- tion of its elements. It is known that many suhstanccs, especially when heated and under i)ressure, have the power of ahsorbing gases. Molten rock would, it is be- lieved, absorb the steam and gases generated by coming in contact with water, and allow them to escape when pressure is relieved or the temperature lowered. A magma forced through the superlicial water-charged layer of the earth's crust, and reaching the surface, would, on account principally of relief of pressure, give olf its oc- cluded steam and gases. If the lava was highly liquid, this would take place by a boiling process, the steam and gases escaping quietly ; but if the lava was viscous, the expansion of the steam would be retarded until its pent- up energy was relieved by an explosion. If the molten lava came in cortact with a considerable volume of water, a ^'iolent explosion would be the inevitaljle result. The above considerations seem to indicate that steam given off by volcanoes is derived from the water-charged rocks through which the lava passes in the upper portions of their conduits, and also that it is distinct in origin from the pressure and heat manifested in connection with it. AVhat is known as dry fusion, that is, the melting of substances from which water is excluded, requires in many, if not in all, instances a much greater degree of heat than when water is present, or what is termed aqueo- igneous fusion. We may reasonably conclude, therefore, that a magma rising in a fissure and entering the water- charged portion of the earth's crust would tend to be- come more fluid. At the same time its energy derived from pressure on the reservoir from which it came would i ■ r ' 306 VOLCANOES OP KOKTir AMKIUCA M) fl'l' I i be increased l)y tliu cxpansivo energy of the steam gen- erated. Lava which would not reach tlie surface by reason of tiie pressure on its reservoir, might, for this reason, aetjuirc! sulli(;ient energy to bring on a surface discharge. Krui)ti()ns when water-charged layers are present might thcu'ofore be expected to bo more numer- ous than in arid regions. Tiiis (juestion has S(mie bearing on the marked association of volcanoes with the ocean, frequently api)ealed to as showing that sea-water gaining access to heated rocks is one of the main causes of volcanic (eruption, but this matter will be considered later.' The instance observed by Squire, cited on a previous page in connection with the description of a young vol- cano in Nicaragua, in which an explosive eruption occurred in connection with the first heavy rainfall that followed the loss of energy after an eruption, is of interest in connection with the considerations just offered. The effect of the rain seems to have been analogous to what would happen if water should be poured on a bed of highly heated furnace-slag ; that is, a steam explosion occurred. There is negative evidence also which tends to show that deeply seated magmas are not in the explosive condi- tion that frequently characterizes volcanic eruptions. We learn from physical students that the tension of water vapor increases with increase of temperature at more than a simple ratio. If the earth's interior is vapor- charged, it must be in a state of vastly greater tension ^I have attempted to correlate volcanoes with humid climates, but although a large majority of volcanoes do occur in humid regions, yet as the surface rocks are nearly everywhere water-cliarged, there does not seem sufficient reason for concluding that this is an important condition govern- ing their distribution. U' '), THEOIlKTrcAI. CONSIDKRATroNS w: than is known from phy.sH^iil cxpcrinicnts or is mani- fest 1)}' tliu most stu^iondous volcjinic (.'X[)I(jsion. Tlic L'f'fuct of Wiitcr in largo volumes on coming in mn- tact Avith liiglily li(Jutu(.l rocks is illnstratcfl hy the eruption of Krakatoa, when something lila» one culiic mile of rock was blown to dust. If the exci'ssivcl}' heated rocks of the earth's interior are steam-chargt'd, the tension under which they exist nmst be at least as many times greater than the explosive energy manifest at Krakatoa as the volume of vapor in the earth's inte- rior exceeds the volume of steam that caused the explosion in the Strait of Sunda. 1 know of no way by which to make a (piantitative measure of the tension of the steam in the earth's interior, inider this hypothesis, but seem- ingly the comparison just made is sutficicnt to show that under the supposition that the steam given off by vol- canoes is derived from the earth's interior and that the highly heated inner sphere of the earth is steam-charged, we would indeed be "living on a volcano." With such a vast volume of superheated steam within the earth, the crust would be at once blown to fragments. Besides, under the generally accepted theory that the earth was at one time much hotter than at present and has cooled from a molten condition, steam, if originally absorbed by the molten magma, must have escaped before a crust conld form. The consideration of wdiat nmst follow in case a vent for the imprisoned steam in the earth's interior, vmder the supposition that the highly heated interior is steam-charged, was once opened, as in the formation of a volcano, is again evidence that such vast tension as the hypothesis implies does not exist within the earth. I 808 VOLCANOES or NORTH AMERICA M. i'iijli I vi B(jtli positive aad negative evidence thus tend to show that volcanic m..gmas rising in fissures and nearing the earth's surface, acquire steam from the water-charged rocks traversed. As the water-charged portions of the eartl). are superficial, volcanic magmas only acquire explo- sive energy on reaching the outer portions of the crust. The influence of various volumes of water in the paths of ascending magmas, and the character of the explosions which would accompany their coining together, remain to be considered.^ Source of the Heat of Volcanoes. — If the reader agrees with me that the source of the steam given off by vol- canoes is in the superficial portions of the earth's crust, it will be easy to understand that the source of volcanic heat and the source of the force that causes molten lava to rise through fissures are distinct and should be sepa- rately considered. From what is now known concerning the progressive increase in temperature with depth below the earth's sur- face, it follows, as has already been assumed, that the source of the heat manifested in volcanic eruptions is the general internal heat of the earth. That is, it is mainly and essentially under the best hypotheses we have con- cernimi; the oriu;in of the earth, the residual heat of a once molten globe. Source of the Pressure which causes Molteu Lava to rise in Fissures. — The pressure to which the rocks composing the earth are subjected increases with depth. Even in the lower portion of what is designated as the earth's ^ A concise disoussion of the causes of volcanic action, accompanied by many references to original treatises, may be found, Prestwich's "Geology," Vol.'l, ISSG, pp. 210-210. { i \ ^ I ( \ THEORETICAL CONSIDEKATIOXS 309 crust, the pressure is so enormous that we might easily ho led to the conclusion that open fissures could nut hv formed. The fact, ho\v3ver, that dikes occur in many regions and frequently in large numbers, sho'vs that the crust has been broken in thousands of localitic^s, and the fissures formed filled by molten rock injected from below. That the fissures thus filled were formed ijolow thousands of feet and even tens of thousands of feet of rock is proven by their occurrence in regions that have siitfercd that amount of erosion. In spite of the natural conclusion that fissures could not be formed in rocks under a vast v»'eight of super- imposed strata, we have the well-known fact that they have been formed in practically countless numljers in such situations. An explanation of this apparent anomal}' is furnished by the hypothesis that the deeply seated rocks, on account of their high temperature, are in what has been termed above a potentially plastic condition. As soon as a break is formed, pressure is relieved ; the rocks to which the break penetrates at once l)ec()me plastic and probably in many instances highly fiuid, and on account of pressure on all sides, except that in wliieh movement is rendered possible by the presence of the fracture, are forced into the opening and rise toward the surface. Although deeply seated rocks are under such enormous pressure that fracture seems impossible, yet the potentially plastic rocks to which the deeper fractures penetrate Jire luider a pressure of an equal order of magnitude. As pressure increases witli depth, the pressure on the deeply seated and potentially plastic rocks are sul)jected to greater lateral pressure than that which tends to close the ;( • ! I X ■'(11 iHnwyigi \ ") 1 i 'li I ) 1(1 1 . 1" ,t 'if 'l, \m 'f 1 , 1 • fl H !) i 4 1 I il f Hi I Li- J! 310 VOLCANOES OF NORTH AMERICA breaks fonned in tho rocks above them. If these prem- ises are correct. — and there seems to be no way of escaping the cunchisions reached, — the result would be that the highly boated rocks reached by a fissure would at once become plastic and would be forced into the break, and would tend to press its walls wider apart. Tl;e ex- tent to whicli a magma would rise in a fissure n-ould depend on several considerations ; chief among whicli would be the pressure on the reservoir from whicli it came, and the resistance it encountered as it rose. The pressure would be determined by the depth of the reser- voir. The resistance met with as the magma was forced upward would be regulated by the size of the break, its regularity, temperature of the magna, lateral pressure tending to close the break, etc. All of the retarding in- fluences, excejjt perhaps the last, may be designated by the term friction. There would be friction against the sides of the fissure, and internal friction in the magma itself, each of which would depend largely on temperature. As the temperature decreased by conduction, etc., the magma would 1)ecome less and less plastic, the friction of flow would increase, and, finally, when solidification en- sued, the motion would cease. For these reasons, a mao-ma entering a larare fissure would tend to rise higher than in a narrow fissure. Dikes deep wnthin the earth's crust should, therefore, be more numerous than in its surface portion. The study of fractures and faults in the earth's crust has shown that such breaks are seldom due to continuous smooth-sided fractures, but are rather splintering breaks, which overlap and cross one another, with many off- shoots. They are more often belts of intersecting fractures r \ .'.»..JWLV .''. ^wiiii'~« H»jrT3.i THEORETICAL CONSIDERATIONS 811 \ ( I \-u than single clean-cut gashes. A magma rising in such a belt of fracture would h?ve to force its way from one break to another, and would send oft' many branches. I think that all geologists will admit tiiat these considera- tions agree with what is found when dikes are studied. From what has just been stated, it follows that the resistance to be overcome as a magma rises toward the surface becomes greater and greater ; as will be shown later, compensation for this progressive increase in resist- ance is found when the water-charged portion of the earth's crust is reached and steam is generated. The considerations just offered, I trust, will make it clear that the siource of the heat manifested in volcanoes, and the source of the pressure which causes a magma to rise in a fissure, are distinct ; and that the force tending to inject a magma into a fissure is the pressure of the earth's crust on the potentially plastic reservoir from which it flows. Differences in Volcanic Lavas. — Objections have been made to the hypothesis that volcanoes derive their lava from the highly heated interior of the earth, on the ground that different volcanoes erupt lava of different composition, and that changes occur in the composition of the lava extruded at different times from the same vent. These oljjections were valid so long as the interior of the earth was thought to be in a molten condition. If, liow- ever, we consider tliat the earth beneath the cold, outer shell is solid by reason of pressure, but becomes plastic as so(jn as pressure is relieved, the ditticulty disappears. The highly heated interior is evidently not homogeneous, as is shown by the products of volcanoes, and as is known also from pendulum observations. M 1*;. : 1 H' 7 1 1 i«M II ( .,) :ii (. 1 i Ml I nr ■J i i ■ * 1 f !i<' 1, H 1 ' 1 j 1 ik ■• J tiki. ■-1 312 VOLCANOES OF NORTH AMERICA Under the hypothesis here advanced, a local relief of pressure, due to the opening of a fissure in the cooled crust, would be followed at once by a local change of the highly heated rocks penetrated, to a plastic or fluid con- dition. The nature of the magma rising in such a break would depend on the composition of the heated rocks reached, and from what we know of the com})osition of both plutonic and volcanic rocks, evidently differs with both lateral and vertical distribution. The reason for variations in the composition of the earth's interior is beyond our present knowledge, unless perhaps, as may be suggested under the meteoric hypothe- sis, the earth has been formed by the coming together of meteoric bodies of various composition. It is known that portions of the earth's crust have been weighted by sedi- mentation and depressed, so that matter formerly at the surface has passed to the highly heated interior. Such transfers of portions of the crust to the interior would produce heterogeneity in the subcrustal portion, and in the very regicju, as will be shown later, where volcanoes most frequently occur, that is, on the borders of con- tinental areas. Independence of Neighboring Volcanoes. — Another objec- tion urged with consistency against the supposition that the earth's interior is in a liquid condition, is that neighbor- ing volcanoes frequently erupt independently and without sympathy one with another. A lofty volcano is sometimes in activity, while a much lower but still active neighboring crater is quiescent. Under the hypothesis here advanced, this objection disappears. If the earth's interior is solid, but in a potentially plastic condition, and branching and irregular fractures are opened from time to time in the THEOUETICAL CONSIDERATIONS 313 crust through which magmas are forced out, it is evident that neighboring fractures may be independent of each other, and also that branches of a main fracture may become closed and opened independently. Origin of Fractures in the Earth's Crust. — In reference to the general cause which produces fractures in the earth's crust, an appeal is commonly made to the effect of the shrinking of the earth on cooling, and the folding and breaking of the rigid crust in order to conform with the shrinking interior. Beyond this general explanation it is not practicable to go in this elementary treatise. Under the hypothesis of a cooling globe it may be sur- mised that while the crust was thin, folding would go on more easily than when a greater thickness was reached ; and that as greater rigidity was attained, fractures would become more common. As the crust thickened, also, its weight would Ijccome greater, and hence the pressure on the still highly heated interior augmented. The conditions leading to the formation of volcanoes should, therefore, increase, at least for a time, as the earth cooled, but as the crust became thicker and more and more rigid, the conditif»ns favoring; the extrusion of lava at the surface would be ex- pected to decrease and finallj^ cease. With a thin crust and comparatively small pressure on the highly heated in- terior, an adjustment of the crust to the shrinking interior would be secured by a moderate extrusion of lava from many breaks; but as the crust increased in thickness, greater eruptions from a decreased number of fractures might be expected. The geological history of the earth seems to be in harmony with these general considerations, since, in North America at least, there is comparatively little evidence of :(';' o If '■■}' M ,1 1 I ' r ij, ,i' 1 1;: 1 : 1 I — ., — *.«■ ' i\ 'i m-i' ■I 814 VOLCANOES OF NOIITH AMERICA volcanic action previous to the Jura-Trias. The great volcanoes, not only of this continent but of the world, belong to Tertiary and more modern times. This is not because ero.sion has removed the more ancient volcanoes, as is shown by the fact that " basal wrecks " of vol- canoes of older date than the Mesozoic are rare. This is perhaps unsound reasoning, since many " basal wrecks " must be buried beneath later sediments. Geological evi- dence seems to show, however, that volcanic activity in- creased with geological ages, and reached its maximum in Tertiary times. This same line of reasoning leads us to expect fewer volcanoes in the future, owing to the con- stantly increasing resistance to the passage of magmas from the interior to the surface through the thickening crust, but fissures once opened should give origin to vol- canic phenomena on a grand scale. A decrease in the number of volcanoes should be accompanied for a time by an increase in size, but when the crust attained a great thickness all surface manifestations of the internal heat should cease even Ijefore the condition of a completely cooled globe is reached. Association of Volcanoes with the Sea. — As has fre- quently been pointed out, volcanoes, with but few excep- tions, are situated on the sea floor or on islands and along the borders of continents. This has been assumed as evi- dence that the presence of sea-water, or perhaps more properly of a body of surface water whether connected with the sea or not, is one of the conditions controlling the origin of volcanoes ; the hypothesis, still current to some extent, being that sea-water gains access to the highly heated rocks of the earth's interior either through fractures or by percolation, and leads to the generation of m m mmsm p^ "Wt TIIEOUETICAL CONSIDERATIONS 315 of steam, which is followed by eruptions at the surface. The idea of a deeply seated origin for volcanic rocks, and the independence of the sources of the heat and pressure, do not enter into this hypothesis. In support of the hypothesis that volcanoes are initiated by the access of sea-water to the highly heated rocks 1)0- neath the crust, it has been pointed out by various geolo- gists, that the gases evolved from volcanoes are frequently such as might l^e produced by the decomposition of sea- water. It has been shown, notably in the case of Vesu- vius, that the country about a volcano after an eruption is sometimes whitened over large areas with common salt. The force of this argument, however, is weakened when we remember that volcanic conduits frequently pass through great thicknesses of stratified rocks, which are sea sedi- ments and were changed at the time of their deposition with saline water. Many portions of the outer layers of the earth are known to be saturated with sea-water ; and m several regions, some of them of broad extent, there are beds of rock salt. Evidently, then, volcanoes might erupt substances like those contained in sea-water, or gases formed by their decomposition, without any direct connection with the sea. The origin of the steam of volcanoes, as has been shown, can be accounted for by the passage of molten lava through water-charged rocks. It has been pointed out that the rocks beneath land areas are generally water-charged from surface precipitation. These considerations, it seems to me, remove all support from the hypothesis that volcanoes have a necessary conne>,tion with surface water-bodies. The fact still remains, however, that volcanoes occur prin- cipally on the borders of continents. I " r ii I 'M r 1 It U% I M II ■ .\ mim If ii 816 VOLCANOES OF NORTH AMERICA Several geologists htavo stiuliefl the distribution of oceans and continents and sought to explain their ori- gin. It is known that these greater features of the earth's surface have been somewhat well defined for geological ages. In fact, the continents and oceans were outlived l)efore the appearance of the first known fauna on tlie earth. Dana has sought to explain the origin of continents by saying that their borders were " original lines of weakness " in the earth's crust, and that movements along these lines, or more properly, belts, have been continued to the present day. What determined the original lines of weakness remains un- explained. The questions that here present themselves are too wide-reaching to be discussed at this time, even if I had the ability to do them justice ; but enough seems clear to explain the distribution of volcanoes, and to show that they have no direct and causal relation to existing water-bodies. The borders of continents, as is well known and, I think, universally conceded by geolo- gists, are belts along which repeated movements have taken place. They are belts along which the folding and fracturing of the earth's crust have been most fre- quent. Being belts in which fractures have occurred, they are the regions where molten rock forced through the fractures has given origin to volcanoes. The pres- ence of volcanoes on the borders of continents is, then, the result of some antecedent condition, which estab- lished belts of weakness in the earth's crust. Along these belts, movements have taken place on account of the earth's shrinking on cooling, and also by reason of the shifting of material on the earth's surface, and possibly other causes. i H ■r I"' THEORETICAL CONSIDERATIONS 817 There are lines of fracture remote from the sea, — as in the Great Basin region, to the east of tlie Sierra Nevada, — and in sucli regions volcanoes occur hundreds of miles inland. The only logical conclusion in refurence U) the distribution of volcanoes, which seems at all ten- able, is that they occur where fractures have been made in the earth's crust, and that they are not necessarily dependent on the distrilnition of land and water on the earth's surface The association of volcanoes with tlie Ijorders of continents nuist, tliurefore, be considered as of the nature of a coincidence, the boundaries of continents and the distribution of volcanoes having been determined ])}• a common cause. Influence of Water on Volcanic Eruptions. — Although there does not seem to be a genetic relationship between volcanoes and surface waters, yet water dues play an important part in determining the nature of volcanic eruptions and even in producing discharges of molten rock. If we imagine a fissure formed in dry rocks, and a molten magma forced through it to the surface, the result would be an overflow of lava. If the lava is in a condition of "dry fusion," — that is, fusion without water above that chemically combined, — the outflow at the surface would be similar to what occurs when molten slag is drawn off from a furnace. The eruptions would be of the quiet type, and not accompanied Ijy explosions. Under these conditions, the lava nmst lose more and more heat the higher it rises in the earth's crust, and consequently becomes less and less plastic. In many instances, it may be imagined the lava would rise near to the surface, but be checked in its ascent by \ ' ;l |l 818 VOLCANOES OK NOltTH AMKUIf'A :#f ■ I ti :il l)econiing too rigid to be forcuil out. The friction of flow would increase in an inverse ratio to the plasticity of the magma. If, however, this stage is reached in water-chai'ged rocks, steam will be generated and ab- sorbed, the highly heated lava will become more fusible on account of the pressure of occluded steam, and there- fore capable of being forced out by a pressure that it would successfully resist if it had not come in contact with water. Viscous lava, also, on coming in contact with large bodies of water in the earth's crust, might generate sufficient steam to blow out a passageway to the surface. Even from this brief statement, it will be seen that water in the superficial portion of the earth's crust has an important influence not only in varying the character of volcanic eruptions, but of inducing surface discharges in cases where the pressure from beneath fails to force a magma to the surface. Force is added to the upper portion of a lava column which is not present before it enters the water-charged rocks. This force — the tension of steam — is added to the force derived from pressure deep below the surface, and is accountable for many (jf the phenomena attending eruptions. The importance of this added force is so great that it has been mistaken for the primal cause of volcanic extrusions. In brief : during volcanic eruptions, there is a rise of molten or plastic rock through fissures, and a descent of surface water through fissures and by percolation ; the meeting-place of these two important elements is in the superficial portion of the earth's crust. The maximum depth to which surface water penetrates is probably not over 30,000 feet, and, in general, the quantity of water f^mt m^ TII K( )UETI(' A L C( >NSI I )EU ATKINS nv.) I J present in a given volume oi rock increases from near that (le})tli to tlie snrfaee. In addition to water [M-rcolat- ing downwaril, there is water in the case of si'dlmentary layers wliich Avas retained by them at tiie time of their deposition . Other Hypotheses The exphmaticms offered in tlie preceding [)ortions of this oliapter, in reference to tiie nature and origin of volcanic eruption, differ from most of tiie previously entertained hypotheses that have heen advanced to ac- count for volcanic phenomena; and, in justice to the stndent who obtains his first introduction to volcanoes from these pages, it is proper that at least sonu; account of explanations previously offered should be given. Space will not permit more than a glance into this branch of the subject, but, from the references given, the reader will be enabled to compare hy[)otheses for hliiiself and be led to independent conclusions.* Chemical Hypothesis. — In an early stage in the study of volcanoes it was suggested that the interior of the earth consists of unoxidized alkaline metals, and that the penetration of water caused oxidation to take place with the production of great heat. This hypothesis, although advocated by Davy and Danbeny, was linally abandoned by the former, and now is of historic interest simply. The products of volcanoes show that conditic^ns even ^ Discussions of various lij'potlieses advanced to account for volcanic phenomena may he found in the following books: G. I*. Scrope, "Con- siderations of Volcanoes," London, ISJ"). J. W. Judd, " Volcanoes," New York, 1881, pp. 3;n-3G!). Joseph Piestwich, "Ceoloov," Vol. I, ISSH, j>p. 210-216. Joseph Prestwich, "On the Agency of Water in Volcanic Eruptions," in Royal Society of London, Proceedings, Vol. 41, 1880, pp. 117-173. ■ m i. i! ii|i I m>^ ■ I ■n ^, ^y^^- SU. *^^ W^^ IMAGE EVALUATION TEST TARGET (MT-3) i6 1.0 I.I 11.25 1^ lli^|Z8 ■^ Uii |2.2 US lU 12^ ■ 40 ■ 20 -► ^ V2 /-^ W # v^^.;^ z;^ '/ Sciences Corporation 23 WiST MAIN STRSET WEBSTER, N.Y. UStO (716) S72-4503 ■^ ^ A ■^W^Tlpi i» . i| U I ■wri^iiw »« M W 320 VOLCANOES OF NOllTH AMERICA I,. ' remotely similar to those postulated do not exist in the regions from which volcanic rocks are derived. Mechanical Hypothesis. — It has been suggested by Mallet ^ that when movements in the earth's crust occur, as when rocks are folded or faulted, the fricl.ion is such that sufficient heat is produced to fuse rocks and bring on volcanic conditions. The movements of rocks referred to unquestionably result in the conversion of some of the energy expended into heat. Such earth movements, however, are believed in most instances to progress slowly, so that the heat pro- duced is diffused by conduction, etc., and a temperature necessary to fuse rocks would not be expected to be reached in most instances. Besides, in many regions, as for example in the Appalachians, there has been intense folding and much faulting, but volcanoes are absent. The walls of great faults and the surfaces brought in contact by overthrusts do not, so far as observed, exhibit evidence of fusion having occurred. Recent theories concerning the metamorphism of rocks ascribe profound changes in mineralogical and chemical composition to the effects of dynamical changes, which certainly favors the views ex- pressed hy Mallet. On the whole, however, the mechanical hypothesis has not been generally accepted by geologists, and does not seem to adequately explain many of the phe- nomena associated especially with intruded rocks, which, so far as their genesis is concerned, must be studied in connection with surface extrusions. Steam Hypotheses. — The consideration that steam is the main propelling force which causes lavas to rise 1 " On Volcjiuic Energy," Philosophical Transactions of the Royal Society, 1873, p. M7. ^mm^mm i^ THEOKETICAL CONSIDEUATIONS 321 through fissures in tlie oartli's crust, lias ah'eiidy been re- ferred to, and several objections to it suggested. Hypothe- ses based on the idea that steam, which plays sucli an important part in many eruptions, is in reality the main cause of the rise of lava from deep within the earth, have been advanced with various modilications by Scrope,' Lyell,^ Judd,""^ Reade,'* and others. Objections to the hypothesis thai steam is the main source of the energy which brings about volciinic erup- tions, have been formulated by Prestwich, and still remain mianswered. In addition to the considerations referred to, others might be enumerated in reference to the nature and origin of intruded igneous rocks, for the reason, as already urged, that intruded and extruded rocks result from variations in a single process. The criticisms on what I have termed the " steam hypotheses " by Prest- wich ^ are as follows : "(1) If the molten mass were so permeated by gases and vapors, the eruption of lava and the discharge of vapors would always be concurrent, and there could be no discharge of the one without the accompaniment of the other ; whereas there are many eruptions which are al- together explosive, while in other eruptions — many of them very large — the flow of lava is effected quietly and without the detonations and ejections caused by the explo- sion of vapors. (2) Another objection is that all lavas would be more uniformly scoriaceous, and that vapor 1 " Considerations on Volcanoes," London, 1825, pp. 17, 66. 2 « Principles of Geology," tenth edition. Vol. II, p. 221. 8 " Volcanoes : what they are and what they teach," New York, 1881, pp. 33, 30, 331-369. * " The Origin of Mountain Ranges," London, 1880, pp. 253-265. 6 Joseph Prestwich, -'Geology," Vol. T, 1886, pp. 212, 213. ■ . i 1:1 f i 1 i u f , I I; 322 VOLCANOES OF NOKTH AMEUICA ■':! i j I MS Ul .:i, bubbles would show themselves more generally ; but there are lavas which are perfectly compact, although they have outflowed under the usual atmospheric pressure, (o) Again, it is difficult to conceive how these vapors and g'lses could have become incorporated with the molten magma, unless we admit, with Dr. Sterry Hunt, that be- tween the solid crust and the solid nucleus of the earth, there is a layer consisting of the outer part of the 'origi- nally congealed mass, disintegrated and modified by chemical and primitive mechanical agencies and impreg- nated with water, now in a state of igneo-aqueous fusion ; or with Mr. Osmond Fisher, who connects volcanic erup- tions with the extravasation of a primogenial water-sub- stance in the molten magma. Otherwise, that water could find its way down to the volcanic foci through the crust of the earth is highly improljable, as a point must be reached where there is reason to suppose the tension of the vapor will equal the hydrostatic pressure of the descending water and stay its course. Further, if such were not the case, not only the volcanic, but likewise the plutonic, rocks would have been subjected to ejection under the same conditions and with similar subaerial results. " Another hypothesis, which also assumes water to be the prime motor of eruption, but considers its introduction to the volcanic foci to be coincident with the eruption itself, supposes fissures to be formed in the bed of the sea, by which a direct passage is opened for the sea-water. The objections to this hypothesis are, that it is not possible to suppose a fissure down which water could have passed without its forming a passage for the escape of the lava itself; nor can we conceive the steam, if so THEOKETICAL CONSIUEllATIOXS 328 •^y be produced, could have had the force to eject a column of Liva of the height required to reach froui the volcanic foci to the summit of the volcano, or that it would take the longer, more resisting, and more indirect channel in presence ol the open and unobstructed fissure." An exhaustive discussion of all the various hypotheses that have been advanced to account for volcanic phe- nomena, is impracticable at this time, but this chapter would be markedly incomplete without a reference to a modification of the steam hypothesis recently proposed by Shaler.' The essential features of the hypothesis re- ferred to are that oceanic sediments of which most strati- fied rocks are composed, are charged at the time of their deposition with sea- water, and may attain great thick- ness. As layer on layer of strata are laid down, the base- ment portion of the pile becomes heated by conduction from the earth's interior; the successive layers acting like blankets in retarding the escape of the heat of the earth. As stated by Shaler : " We thus see that in the water imprisoned in the deposits of the early geological ages and brought to a high temperature by the blanketing action of the more recently deposited beds, we have a sufficient cause for the great generation of steam at high temperatures, and this is the sole essential phenomenon of volcanic eruptions. "We see also by this hypothesis why volcanoes do not occur at points remote from the sea, and why they cease to be active soon after the sea leaves their neig;hborhood. . . . " The foregoing considerations make it tolerably clear that volcanoes are fed from deposits of water contained 1 X. S. Shaler "Aspects of the Earth," Xew York, 1889, pp. 46-97. Also, "Scribner's Magazine," February, 1888. f TlfilW^PI 3-24 VOLCANOES OF NOKTH AMKItICA i 'i in iincioiit rock.s whi(.^li liavu bocoino greatly heated tlirouuli tlie blanket iiiL!; ei'fects of the strata which have been laid down upon them. The gas which is the only hi variable element of volcanic eruptions is steam ; more- over, it is the steam of sea-water, as is proven by analysis of the ejections. It l)reaks its way to the surface only on those parts of the earth whicih are near to where the deposition of strata is lifting the tem[)erature of water contained in rocks by preventing, in fact, the escape of the earth's heat." In answering probable objections to this hypothesis, its author states that the only seriou?: question arises in ref- erence to the thickness of the rocks which have been laid down on the sea floor. In this connection it is remarked: " Hardly any geologist will doubt that it is entirely within bounds to assume that thickness to exceed twenty miles. It may well have attained twice or thrice that depth since the geological ages began." In reference to the statements made in the last quota- tion, it must be acknowledged that the thicknesses of stratified rocks assumed are purely a matter of opinion; no such thickness of stratified beds in one pile has ever been observed. Instead of subscribing to the state- ment that geologists are practically agreed as to the vast thickness of stratified beds, I, for one, must dissent from such a conclusion until proof is advanced to sustain it. Whatever the aggregate thickness of sedimentary beds deposited during various geological ages may be, the essential part of the hypothesis is that the sedimentary beds should be immensely thick in a given locality. Marine sedimentation usually continues only so long as subsidence carries the added material below sea level. m pi THEOKKTICAL CONSIDEnATrOXS 325 An increase in the thickness of sedinientary hcds will cause a rise of temperature in tlieir l)asal portions espe- cially, as claimed hy Shaler, hut this means an increase in volume, and, as [)ointed out hy Ueade and others, an elevaticm of the surface. It appears, therefore, in locali- ties where thick sediments accunudate, that an excessive thickening should he checked, if for no other reason, by elevation due to rock expansion, which -would carrv the surface ahove sea Ic'vid, and such excessive.' thicknesses of stratified beds, as is essential to the liypothesis referred to, C(juld not he expected to occur. One of the deepest sections of stratified rocks, consist- ing largely of Paleozoic sediments, yet measured in America, occurs in the middle Ap})alachiau region, but volcanoes and volcanic rocks of post-Paleozoic date are absent. The thickness found is not enough, to be sure, to meet the requirements of this hypothesis, but it apjjcars to be one of the best test cases that can be sun-wsted. The claim made in the liypothesis under considera- tion — that steam is the sole essential phenomenon of volcanic eruptions — has been considered on previous pages, where the evidence of the independent origin of the pressure, heat, and steam manifest in volcanoes has been presented. If the reasons for considering the essential independence of these chief causes for volcanic phenomena are valid, it is evident that to account for tlie escape of steam during a volcanic eruption will not furnish a com- plete theory of the origin of volcanoes. The student will find on reading Shaler's very interest- ing and suggestive paper, that the essential connection between volcanoes and subterranean intrusions of molten rock is not fully recognized. When the fact that dikes. HP Hi' t'n h It !< 1 I i '\t '■ 'i n u i 826 VOLCANOKH OF NOUTIl AMKIMCA i'! n M intruded sheets, plutonic plugs, Inccolitcs, subtuberant in(juntain.s, and volcanoeH result from variations in one general process, is admitted, and it seems to me the con- clusion is well founded, this general view at once does away with the assumption that steam is the sole cause of volcanic phenomenon. These same considerations must lead us to put aside the long-cherished hypothesis that there is an essential and, to volcanoes, a vital connection between extrusions of molten rock and the distribution of surface water-bodies. In all of the hypotheses that have been advanced in which steam is considered as the prime motor, the point of view is that obtained by an observer looking down into craters like those of Vesuvius or Stromboli, when in mild activity. The phenomena of the boiling of the liquid lava and the escape of great bubbles of steam are then the prominent facts. To account for the steam observed in such cases, seems to be the chief feature of the problem ; the rise of the molten lava from miles below the surface, the conditions under which it exists in the reservoir from which it flows, and the changes it undergoes as it nears the place of discharge, are lost sight of in the presence of the striking activity in progress at the summit of the lava column. If in imagination we change the point of view, and see the reservoir miles below the surface, the conduit, perhaps with many branches leading upward, the upward flow of the molten rock through the conduit, the descent of sur- face water, — and also the presence of water in stratified beds, — to meet the rising magma, etc., it must appear that the " sole essential phenomena "to be accounted for are not the presence of steam. *■!!; CHAPTER YIII ''1 H THE LIFE HISTORY OF A VOLCANIC MOUNTAIN One of tlie pliases oi modern geograpliical .study is the tracing of the successive changes that the various feat- ures of the hind pass through from their initiation to their disappearance. As is well known, even the most magnificent mountjiins that give diversity to the earth's surface at the present day, have had their time of jjirth and growth, and have perhaps reached full maturity, ))ut are one and all crumbliui^ before the attacks of the de- structive agencies of the atmcjsphere and will ultimately be removed. The record of such a series of changes in topographic forms from youth to maturity, old age and final disappearance, may with propriety be termed a life history. The life history of a volcanic mountain should evidently begin with the changes deep within the earth that lead to its birth. These prenatal causes, however, are such an intimate part of a still greater history — the development of the earth itself — that it would lead too far from our immediate theme to begin a review of the history of a volcanic mountain with a discussion of the conditions which antecede its appearance as a topographic feature. When a fissure is formed in the earth's crust through which molten rock is forced upward to the surface, there may be an overflow throughout a considerable extent of the break and a fissure eruption ensue ; but more commonly 327 I '\ ■ J n 328 VOLCANOKS or NOKTH AMERICA the escape of lava is restricted to certain circumscribed localities about whicli volcanic; inonntains are built up. Whether a volcano shall belong to the (juiet or the explo- sive type depends on various conditions, some of which have been discussed in the preceding cluqjters. Volcanic erujjtions thus i)resent great diversity and lead to topo- graphic changes with widely varying characteristics. A complete di.scussion of the lifj histories of the many topo- graphic types due to igneous extensions would embrace the origin, dissection, and disappearance of vast lava i)lains like those dramed by the Columbia ; the birth, growth, decline, and death of mighty domes with plateau-like summits of the Hawaiian type, and of the conical piles of lapilli and scoria represented by the sacred mountain of Japan. It is difficult to group such varied phenomena in a single picture. Let us, instead, select a single individual from the most numerous class of volcanic mountains, — the composite cones formed largely of projectiles, but bound together by lava streams and dikes, — and endeavor to review the principal changes it experiences during its life span. It is possible that the aborigines of the Pacific coast witnessed the advent of some of the giant volcanic peaks which now give dignity and grandeur to the scenery of that promising land. Could we have stood with some primitive hunter, armed with flint-pointed arrows and stone axe, on the granite hills commanding a view of the fair Tertiary plains of Oregon and Washington, we would have beheld a sylvan scene as beautiful in its varied charms as any landscape our broad continent presents to-day. Let us take such a backward journey. To the flight of fancy a million years are but as a day. wmmm nil: Line iiistouv of a volcanic mointain :{:2i> From our coiiiiimiiding station on the Tortiarv uplands, furest-covurc'd liills and hroad verdant valleys are spread before us. A gleam as of burnished silver here and there amid the dense forest of the plain marks the course of a noble river. I^akes eiudosed by walls of verdure add an indescribable charm to the scene. Between the banks of purple formed by the distant hills, we catch glimi)ses of the shiinuiering sea. The general features of the broad hmdscape, the shadows of passing clouds on the summer foliage, and the ever-varying tints of sea and sky are the same as the dwellers A the earth see to-day, — and yet do not .see, so familiar are they. liut little in the viiried details of the scenes about us is familiar, except the crys- tals in the granite beneath our feet. Should we descend from our chosen station, we would find that the trees and flowers in the forest are strange to us. The birds and insects that fill the air with music are all unfamiliar. The mammals that roam the forest and haunt the river banks and lake shores are still more novel. We have gone so far back in the history of the earth that the i)lants and animals are the ancestors of the present flora and fauna ; yet the Tertiary is only the day-before-yesterday of geology. We are in the sunny summer-tide of the earth wliicli preceded the Glacial winter. Our reveries are broken by an earthquake shock. A fissure has opened in the broad, forested plain, and a vast column of vapor is rolling heavenward. Explosions hurl great rocks high in the air, some of which fall in the adjacent forest. The vapor column is darkened by dust, which drifts away before the wind, and for miles to lee- ward the vegetation is whitened as if by snow. The trees are denuded of their branches and in places buried v. I i I'll i ( Kn i :' 330 VOLCANOES OK NOIITII AMKKKA from si^ht. A roar mm if of iiiinjL;;l('(l tliiiiKlur craslies makes the air vibrate. With uacli explosion the earth trembles. The cloud of dust-laden va^jor expands and soon the entire land is in shadow. As the air ^rows dense about us, the sun assumes strange hues. Lightning (lashes seem to tear the dense veil asunder, but the aocom[)anying thundei' is lost in the deafening roar of escai)ing steam and the crash of coimtless ex[)Iosions. Altliough it is midday, the blackness of a starless mid- night .soon conceals the dreadful scene. Strange cries of terror-stricken beasts come; from the neighboring forest. Birds of unfamiliar i)lumage, regardless of our presence, perch on the rocks about us. Our Indian companion prostrates himself in woiship. Days pass before the sun again ai)pears and reveals a scene of death and desolation where before all Avas life and beauty. Where the vapor was first seen to rise, there is a conical hill of black iind still steaming rocks, — an infant volcanic mountain. In its summit we can discern an opening or crater, from which a great volume of steam is rolling out. Occasionally the vapor column is darkened by dust and scoria shot upward by explosions within the crater. During periods of decreased activity we might walk over the desolate plain of lapilli and dust, and if a strong wind should be blowing, climb the wall of the crater and look down upon the red-hot, liquid rock that surges in its depths. At night the light from tiie molten lava is reflected by the cloud above it. The under surface of the expanded summit of the vapor colunm is all aglow with lurid light, while the undulat- ing upper surface is dark or perhaps has ; silvery white- ness in the moonlight. THK LIFE HI.STOIIV OF A VOLCANIC MOI'NTAIN Ml At Viiryinu the hill is huilt higher, and at length attains the dignity of a mountain. The volcaniit mountain is a])j)roaching maturity. It rises with, all the symmetry and freshness of youth, as a cone with long, smooth, gently concave slopes, which merge imperceptihly with the surrounding ])lain. Ahove its sharp summit a cloud is usually visihle which the winds dist I "h m. > 338 VOLCANOES OF NOUTH AMERICA be Hiifficieiitly elevated above tlie sea, or if earth move- ments during the long history we have briefly reviewed liave upraised it, erosion will cut away the rocks to :u\ horizon below that of the valley in which the volcano had its birth, and reduce the entire region to the level of the sea. In other words, the land, with whatever topographic forms it may have possessed, will be eroded to base level. A geographical cycle will then have come to an end. Some thoughtful man in the far distant future will walk over the plain beautiful with a new flora, and find the dikes of plutonic rock that occupy the Assures in the earth's crust from which came the material used in build- ing the vanished mountain. •'*■ m INDEX Aa surfaces of lava streans, 59-02. Ahif'S rdigiiisa, mention of, 170. Acid lavas, fusibility of, 'u, 58. Acid rocks, term explaim-d, li:). Adams, .Mt., \Va.sh., brief account of, 2.'J9, 240 ; hei.ijht of, 2:!4. Agates, origin of, 04. Agua, Volcan de, description of, 108- 171. Aguilera, J. S., cited on volcanoes of Mexico, 170, 181. Ahuacatlan, description of, 189. Akutan, Alaska, eruptions of dust from, 79. Alaska, deposits of volcanic dust in, 288, 289 ; volcanoes of, 2(')7-28;i. Alece Springs, Australia, sound of eruption of Krakatoa heard at, 27. Aleutian Islands, central and western, volcanoes of, 282. Aleutian volcanic belt, description of, ■ 268-270. Amygdaloid, nature and origin of, 64. Analysis of the gases of volcanoes, 62. Analyses of volcanic dust, 292. Anderson, Capt. , cited on Bogosloff , 280. Andesite, brief account of, 124, 126. Arizona, volcanic mountains of, 192, 193. "Ashes," volcanic, a misnomer, 75. Baker, Mt., Wash., brief account of, 245, 240 ; height of, 2'^1. Bangkok, Siani, sound of eruption of Krakatoa heard at, 27. Barbour, E. II., cited on volcanic dust, 280. Basalt, brief account of, 121, 122. Basaltic structures, in dikes, illus- trated, 97, 98. Basic lavas, fusibility of, 57, 58. Basic rocks, term explained, 113. Becker, G. F., cited on the profiles of volcanic mountains, 82. Biihveli, Lake, Cal., reference to, 2.'1]. Ilig Horn Mountains, cited as an ex- ample of subtuberant mountains, l(i4. lUackfoot basin, Idaho, basaltic craters in, 258. Black Hills, Dakota, cited as an exam- ple of subtuberant mountains, 104 ; plutonic jilugs near, 102. Blomidon, Nova Scotia, reference to rocks of, 121. Bogosloff Island, Alaska, description of, 270-281. Bombs, volcanic, nature and origin of, T.i, 74. Bonneville, Lake, mention of, 198, 202, 205. Bonney, E. \V., cited on volcanic dust from Cotopaxi, 79. Boulders of disintegration, reference to, 98. Brakleast Hill, Mass., volcanic dust from, 290. Breccia, definition of, 00. Brigham, W. 'P., cited on volcanoes :!-1W); cited on palioehoe surfaces of lava streams, 02, 0;j ; cited on I'ele's liair, 72, 7;^ ; citt on tiie volcanoes of tlie Hawaiian Islands, ;]0-o3. Eartlniualtes, rents formed by, 00. Edgecumbe, Mt., Alaska, mention of, 208. Ellensburg, Wash,, dikes near, 2.")2, Emmons, S. F., ascent of Mt. Kainier, Wash., by, 242-245; cited on Mt. St. Helen's, Wash., 240; cited on Mt. Pitt, Ore., 2:!0 ; and A. Hague, cited on Ragtown ponds, Nev., 200. Endlich, F. M., cited on the Spanish peaks, Col., 200, 201 ; cited on vol- canic cones in Colorado, 2u8, 259. Erosion of volcanic mountain?, 90-04. Etna, Mt., mention of, 1 ; reference to fissures in the sides of, 37; extruded and intruded igneous rocks, 00. Felsite, term explained, 112. Ferrer, cited on height of Orizaba, 173. Fissure eruptions, Columbia lava from, 252 ; description of, 30-43. Flagstaff, Arizona, volcanic mountains near, 102, 193. Flames accompanying volcanic erup- tions, 51. Fouqu6, cited on gaseous products of volcanoes, 49. Fragmental products of volcanoes, 69- 80. Fuego, Volcan del, Guatemala, de- scription of, 104-108. Fumarole stage in volcanoes, brief ac- count of, 46. Fumaroles, on Izalco, San Salvador, 140. Fusibility of lava, causes of variation in the, 50. Fusiyama, Japan, reference to, 81. Gabb, W. M., cited on volcanoes of Central America, 130. Galindo, Juan, cited on eruption of Conseguina, 102. (laseous products of volcanoes, 49-53. (iases of volcanoes, analysis of, 52. Geological survey of ("anada, reference to, 200. Geikie, Archibald, cited on Columbia lava, 255 ; cited on gaseous products of volcanoes, 51 ; cited on lava Helds of Eurojie, 43. Giant's Causeway, Ireland, reference to, 121, 251. Giblis, George, cited on Mt. Hood, 230, 240. Gilbert, G. K., cited on the Ice Spring craters, Utah, 198-202 ; cited on lac- colitfs, 10.'» ; cited on volcanic moun- tains of Arizona, 102. Glacial deposits in Central Washing- ton, 2'i0. Glaciers of North America, reference to, 225. Golden, Col., volcanic cones wear, 250. Gorman, M. W., cited on Mt. Hood, 238 ; cited on Mt. St. Helen's, 241. Grand Coulee, Wash., brief account of, 250. Granite, brief account of, 118-121. Grant, U. S., cited on volcanic dust, 289. Great Plains of the Columbia, 255. Grewingk, C, cited on Alaskan vol- canoes. 270. Guatemala, list of volcanoes in, 130. Hague, Arnold, cited on Mt. Hood, Ore., 230 ; and S. F. Emmons, cited on Ragtown ponds, Nev., 200. IIa»vaiian Islands, aa surfaces of lava streams on, 50-62 ; brief description of volcanoes of, 29-36 ; reference to rocks of, 121. Hawaiian volcanoes, eruptions of lava from, 55 ; rate of flow of lava from, 57. Hayes, C. W., cited on volcanic dust in Alaska, 288. ^■H I >l >v ■ i \t.. '< ) 'i I' 1 1 * .1:.' I J i!t 842 1NI>KX Ilealy, M. A., cilcil (m IJdnosloff, 278. Hfiif of till' iiitt'iior of tlic cartli, 2'.I7. ll(il|ii-iii, Aiii{ulo, cited on uNciiit of Orizaba, Mex., 17u, 170 ; cited on h('if,'l»t of Orizaba, Mex., 174; cited on volcanoes of Mexico, 170, 180, Henry Monntains, I'tali, cited as type of laccolitts, lo;i. Herculaneuni, Italy, reference to de- strnction of, 10. Hdlyoke, Mt., Ma.ss., reference to rocks of, 121. Honduras, li.st of volcanoes in, 1.'18. Hood, Mt., Ore., brief account of, 237, 238 ; liei-ht of, 234. Hook Mountains, N. Y., reference to, 101. Hot springs, origin of tlie heat of, 48. Humboldt, A. von, cited on height of Orizaba, Mex., 173 ; cited on Izalco, 141 ; cited on .lorullo, Mex., ir)2, 163, 155 ; cited on volcanoes of Mex- ico, 172, 179, 187, 188. Hungary, reference to phonolite hills of, 83. Ice Spring craters, Utah, description of, 198-202. Iddings, J. P., cited on rock from Mono Valley, 210 ; reference to book trans- lated by, 115. Igneous intrusions, nature of, 94-106. Igneous rocks, characteristics of, 100- 120; classification of, 111-118. Iliamna Volcano, Alaska, description of, 271. Ilojiango Lake, San Salvador, volcanic eruptions in, 147, 148. Imbricated mountains, structure of, 84. Intermediate rocks, term "explained, 114. Intruded sheets, nature and origin of, 90-101. Intruded and extruded igneous rocks, 09. Intrusions of igneous rock, 99-106. Intrusive rocks, relation of, to volca- noes, 301-304. loanna Bogosluva, see Bogosloff. Isle of Staffa, Scotland, reference to, 251. Fxtacciluiatl, Mex., description of, 183, 1H4 ; height of, 17». Izalco, San Salvador, dt-scriptlon and Idslory of, 141-140; mention of, 140. .Jamaica, fall of volcanic dust in, 100. •Jan.ssen, cited in the gase.s of volcanoes, 52. Jefferson, Mt., Ore., brief account of, 230, 237 ; height of, 234. John Day system, reference to, 253. Johnson, VV. 1)., map by, 213. JoruUo, Mex., history of, 152-150; mention of, 140 ; San I'edro de, mention of, 153. Judd, J. \V., cited on eruption of vol- canic dust in Iceland, 70, 77 ; cited on the composition of volcanic va- pors, 53 ; cited on commercial prod- ucts of volcanoes, 4(i ; cited on the nature of volcanic eruptions, 36 ; cited on the profiles of volcanic mountains, 82 ; cited on Stromboli, Italy, 3-0 ; cited on tiic .structure of lapilli cones, 85 ; reference to book by, 115,310,321. June Lake, Cal., glacial and volcanic records near, 224. Kemp, J. F., cited on composition of rhyolite, 124 ; reference to book by, 115. Kilauea Volcano, Hawaiian I.-slands, brief account of, 32-34 ; profile of, 81. King, C, cited on Ragtown ponds, Nev. , 200. Krakatoa. description of, 22-29 ; dust erupted from, 70, 77, 290, 294 ; ref- erence to eruption of, 104. Krukenborg, C. Fr. W., cited on Pele's hair, 72. Labradnrite in basalt, 121. Labuan, Borneo, sound of eruption of Krakatoa heard at, 27. Laccolites, brief account of, 102, 103. Lahontan, Lake, mention of, 205. Landivar, Raphael, mention of, 153. Lapilli, character of, 75. Lapilli cones, structure of, illustrated, 85. INDKX ;n:j dust ref- 'ele's J3. Ued, Lnsspii's Peak, Tal., description of cinder cone mar, li^H-^ol. Lava Walla, rcaumliiing voleaiiie bunilis, 74. Luva Park, Cal,, notice of, li-'tl ; HtreaniM. eliaracteristics of, 54-71. Le Oonle, Joseph, cited on eartli(|uako ti.ssures, \M ; cited on thiclcnes.s of ('(ilunil)ia lava, 251. Lite history of a volcanic mountain, ■.',27, :5:{H. Lipari LslandH, Italy, mention of, L Liparite (Uliyolite), brief account of, 1211-124. Livin,i;ston,.I. W., olwervations by, 150. Loa, Mauua. See Manna Loa. Lobley, J. L., cited on structure of Vesuvius, 87 ; cited on Ve.suviu.s. 17. LoesH, volcanic du.st associated witli, 280. Lou'iin, Mt., reference to lieii;htof, 173. Lower California, volcanoes of, IIK). Lyell, Charles, cited on Monte Nuovo, 14(1 ; reference to works of, 321. Lyell, Mt., Cal., mention of, 210. Macrocry.stalline, term explained, 113. Magma, term defined. 111. Makushin, Mt., Alaska, mention of, 281. "Mamclons" of the Lsland of Bour- bon, reference to, 83-85. Marvine, Archibald, cited cm volcanic cover in Colorado, 250. Mauna Loa, Hawaii, accotnit of, 29- 32 ; illustrating a type of mountains, 80j profile of, 81. Mazama, Mt., Ore., Crater Lake on, 235, 236 ; height of, 234. Mechanical hypotliesis of the origin of volcanoes, 320. Merrill, G. P., analysis of volcanic dust by, 292 ; cited on rocks from BogoslofI, 280. Metamorphism, contact, reference to, 97. Meteoric hypothesis, reference to, 297. Mexico, height of mountains in, 174 ; volcanoes of, 172-190. Mono Craters, Cal., description of, 217, 225. Mono Lake, Cal., elevation of, 210; reference to volcanoes near, 37. Mono Valley. Cal., vohanic rratcr.s in, 208 ; deposits of volcanic dust in, 285. Mora Creek, N. M., lava flow in, 2tl4. .MciuntainH formed of lava sheets, .s|, 85. Muir's butte, Cal., reference to, 257. Nebular hyixithesis, reference to, 297. Necks, volcanic, in New .Mexico, 193, 108 ; mention of, 93 ; nature and origin of, 80, 90. Negit Island, .Mono Lake, Cal., tlescrip- tion of, 210,217. Neva(h) de Toluca, Mex., height of, 174. Newark system, reference to igneous rocks in, 101, 120; reference to re- port on, 44 ; trap rooks, 4.'!-45. New Hogosloff. See Uogoslofl. New Mexico, brief accmmt of the vol- canoes of, 202-200 ; volcanic moun- tains of. lO.J-198. Nicaragua, li.st of volcanoes in, 138. Nicholson, M. 11., analysis of volcanic dust by, 292. North Mountain, Nova Scotia, refer- ence to rocks of, ;21. North Table Mountain, Col., reference to, 259. Norwa.\', volcanic dust from, 290. Nuovo, Monte, Italy, mention of, 140. OcatC crater, N. M., brief account of, 204. Oldham, R. D., cited n the Deccan trap of India, 39-41. Ordofiez, E., cited on volcanoes of Mexico, 177, 181. Oregon, deposits of volcanic dust in, 287. Oregon and Washington, great vol- canic mountains of, 233-246. Orizaba, Mex., description of, 173; height of, 174. Owen, D. D., cited on columnar dike, 98. Pahoehoe surfaces of lava streams, 62, 63. Palisade trap sheet, N. J. and N. Y., description of, 101; reference to, 121, 251. 1 .344 INDLX 11 ! ( /' \')' :i: I'liliiileri L., cili'il lit) V'psuvius, 17-22. I'aota IhIuikI, Mmiii liUkc, t'al.. (If- Mcrii)ti(m of, 211-210. raviildff volcano, AlaHkn, iiici>iini\ of, realf, A. C, cited on cruUTH in Hlack- foot basin, Idaho, '2M. rtlt''(j iinir, cliaractcr and orifjin of, 71, 72. I'ltidff, Ivan, cited on Alaskan volca- noi'H, li70, 274. rctrniofjy, brief accrxint of, 111-llH. I'liilippinu InlandH, Noiind of eruption of Krakatoa heard at, 27. " I'ine tree of Vesuvius," brief account of, H, IK. I'hiUH M(intczum((, n San Kraiicisco Mountain, Ariz., df- Staffa, Isle of, Scotland, refiicnct to Hciiplioii of, 102, !(•:{. ' roi'knof, I'il. San Salvador, list of volcanoes In, \'.iH. Stau'i f in tlu! liven of vulcaniitH, J.')-lt*. Sand, volcanic, naturt> and niodu of | Stalaftltfii In lava tuniu Is, iiu>nti, 7, nicntiun of, gatti-H Kiven lift' l»y, .'il. Saiu-UH, Mass,, volcanic tlust from near, •JIM). Scorlaceous lava ni tlic liasal portions of lava Htrcains, (itt-()M ; surfaces of lava streams, (5.'{-(l(l. Scott, .Mt., Ort'., liriulit of, 2:)4. ScroiM', (1. 1'., cited on vnlcanoeH of Fraiicf, 1!);5. Sections of rocks, liow made, 116, Slialer, X. S., cited on eruption of Vesnviu.s, 11, 12 ; cited on orif,'in of volcanoes, ;)2.'!-;J2(l. Steam liypotlieHes of the orlniu ot vol- canouH, '.i'2i), '.I'M. Sieplii ns, .). L., cited on eruption if I/.alco, San Salvador, 111-11.'}. Steveiis, Hazard, ascent of .\!t. Uainier i.y. •-•12. Steveii.son, J, J., clcd on volcanoes in New .Mexico, 2ii;!-2t!."j. Stromltiili, Italy, de.seriptiou cif, 2-7. Stroml)olian sla^je of volcanoes brietiy detlned, 11. Structure of volcanic mountains, bil- HM. Sulilinied products of volcanoes, J'i-.-,;{. Sulitulierant nmuntaius, natuie and oriKin of, KHi-lo,'). Sunset Hills, Nev., reference to rocks of, 12.!. Shasta, .Mt., C'al., andesitic rocks of, i Superior Lalxc, reference to iuneou.1 125 ; description of, 225-228 ; refer- ence to, 252. Shastina, Cal., reference to, 227. Sheets, intruded, nature and origin of, 90-101. Shislialdin volcano, Alaska, descrip- tion of, 274, 275 ; prolile of, 81. Siemens, cited on gaseous products of volcanoes, 61. Sierra Nevada Mountains, reference to structure of, 247. Sinj,'apore, sound of eruption of Kra- katoa heard at, 27. Slag of furnjice, resemblances of, to volcanic rocks, 108. Snake Uiver, Wash., depth of canyon of, 251, 254, 250. Soda lakes, Nev., description of, 205- 208. Solfatara .stage in volcanoes, brief ac- count of, 40. Somma, Mt., Italy, mention of, 8, 13. Spanish peaks. Col., de.scription of, 259-262 ; mention of, 265. Squier, E. G., cited on eruption of Con- seguina, Nicaragua, 159-161 ; cited on Izalco, San Salvador, 141 ; cited on young volcano in Nicaragua, 140, 148. rocks of, i;JO. Symons, T. W., cited on thickness of Ct)lumbian lava, 251. Tabernacle crater, Utah, description of, 2l»2-205. Taylor, .Mt., N. M., description of, 103- 108. Tertiary age of Columbia lava, 253. Three Sisters, Ore., brief account of, 2.">