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THE P0R0ROCA,

OR BORE, OF THE AMAZON.

JOHN 0. BliANNEB, B.S.,
FORMERLY MEMBER OF THE IMPERIAL GEOLOGICAL COMMISSION OF BRAZIL,
CORRESPONDING MEMBER OF THE NEW-YORK ACADEMY
OF SCIENCES, ETC. .

From "SCIENCE," November 28, 1884,
WITH ADDITIONAL NOTES.

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FEINTED BY RAND, AVERY, & COMPANY
18S5.

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THE POROROCA,

OR BORE, OF THE AMAZON.

JOHN C. BRANNER, B.S.,
FORMERLY MEMBER OF THE IMPERIAL GEOLOGICAL COMMISSION OF BRAZIL,
CORRESPONDING MEMBER OF THE NEW-YORK ACADEMY
/ OF SCIENCES, ETC.

From "SCIENCE," November 28, 1884,
WITH ADDITIONAL NOTES.

BOSTON:
PRINTED BY RAND, AVERY, & COMPANY.
1885.

THE 'POROROCA,' OR BORE, OF THE AMAZON.

While travelling upon the Amazon in 1881, 1 was fortunate in hav
ing an opportunity to observe some of the effects of a remarkable
phenomenon which occurs at the northern embouchure of that river,
in connection with the spring- tides. It is known to the Indians and
Brazilians as the porordca,1 and is, I believe, generally supposed to
be identical with the ' bore ' of the Hugli branch of the Ganges, of the
Brahmapootra, and of the Indus.2 I regret very much, that like Con-
damine,3 who passed through this part of the country about 1740, I
could not observe this phenomenon in actual operation ; but the gen
tleman whose guest I was at the time, and upon whose boat I was a
passenger, was fairly horrified at my suggesting such a thing, while
his boatmen united in a fervent ' God forbid that we should ever see
the porordca ! ' and ever afterwards doubted my sanity. I venture,
however, to give some of the results of my own observations, in order
that those who in the future visit this region, concerning which so lit
tle is known, may be able to see, and establish as far as possible, the
rate of destruction and building-up here being carried on.
I was upon a trip from Macapa, — a small town on the northern
bank of the Amazon, and about a hundred miles from its mouth, —
down the river to the ocean, and thence up the Rio Araguary as far
as the last might be found navigable. The one inhabited place on
the Araguary1 is a verjT small military colony, called the Colonia Mili-
1 Pronounce paw-raw-raw'-ca. This word, which is of Tupy or native Brazilian origin, is
the one invariably used hy the Brazilians. Father Joao Tavares says it is probably a frequen
tative form derived from the Tupy word opoe, which means ' to break with a noise.'
2 Similar phenomena, though on a much smaller scale, occur on the G-aronne in France, on the
Wye, Severn, and Trent, in England, and on the following streams in Brazil : Rio G-uama,
Capim, and Mojii in the province of Para, on the Rio Puriis in the province of the Amazonas,
and on the Mearim in the province of MaranbacT.
3 Oondamiue was sent by the Royal academy of sciences, of France, to make astronomical ob
servations in South America in 1735. His brief description of the porordca is the one from
which all references to it appear to have been taken until now.

tar Pedro Segundo. At Macapa I became acquainted with the then
director, Lieut. Pedro Alexandrino Tavares, and was invited by him
to visit the Araguary.
The trip from Macapa was by a small sailboat down the Amazon
to the ocean, and thence up the Araguary. Our departure was so ar
ranged that we could reach that part of the region disturbed by the

EOMTO"

MOUTH OF THE AMAZON. SKETCH-MAP OP THE PART PRINCIPALLY AFFECTED
BY THE PORORdCA, BY J. C. BRANNER.

porordca exactly at the time when there would be the least probability
of its being met with; that is, at the time of the neap-tides. The
voyage down the river was in the face of the wind, and it was only
five days after leaving Macapa that we put into an igarape" on the
Island of Porquinhos to wait for the turning of the tide. I had already
seen islands said to have been half washed away, and others built up,
by. the porordca; and I had seen upon the shores the evidences of its
destructive power in carrying away forests, and cutting away banks :
but it was on this island that I was first able to see some of its effects

near at hand, and at my leisure. After having seen so much, I was
only the more anxious to see the porordca itself ; but my suggestions
in regard to it were answered by an ominous silence on the part of
the director, and my requests by additional expressions of horror.
As I shortly afterwards met and conversed with a man who had
seen the porordca, I shall first give his description of it, and then
speak of its effects as observed by myself. This man was a soldier
iu the Brazilian arm}', and, on the occasion referred to, was going
with a few other soldiers from the colony to Macapa in a small open
boat. Arriving at the mouth of the Araguary, they went down with
the tide, and anchored just inside the bar which crosses the mouth of
this stream, to await the turning of the tide, which would enable them
to pass the shallows, and then carry them up the Amazon. Shortly
after the tide had stopped running out, they saw something coming
toward them from the ocean in a long white line, which grew bigger
and whiter as it approached. Then there was a sound like the rum
bling of distant thunder, which grew louder and louder as the white
line came nearer, until it seemed as if the whole oceau had risen up,
and was coming, charging and thundering, down on them, boiling
over the edge of this pile of water like an endless cataract, from four
to seven metres high, that spread out across the whole eastern hori
zon. This was the porordca 1 When they saw it coming, the crew
became utterly demoralized, and fell to crying and praying in the
bottom of the boat, expecting that it would certainly be dashed to
pieces, and they themselves drowned. The pilot, however, had the
presence of mind to heave anchor before the wall of waters struck
them ; and, when it did strike, they were first pitched violently for
ward, and then lifted, and left rolling and tossing like a cork on the
foaming sea it left behind, the boat nearly filled with water. But
their trouble was not yet ended ; for, before they had emptied the
boat, two other such seas came down on them at short intervals,
tossing them in the same manner, and finally leaving them within a
stone's throw of the river-bank, where another such wave would have
dashed them upon the shore. They had been anchored near the mid
dle of the stream before the waves struck them, and the stream at
this place is several miles wide.
But no description of this disturbance of the water can impress one
so vividly as the signs of devastation seen upon the land. The silent
story of the uprooted tree's that lie matted and tangled and twisted
together upon the shore, sometimes half buried in the sand, as if they

had been nothing more than so many strings or bits of paper, is deep
ly impressive. Forests so dense that I do not know how to convey
an adequate idea of their density and gloom, are uprooted, torn, and

SKETCH ON THE ILHA DOS PORQUINHOS SHOWING THE UPROOTED TREES.

swept away like chaff; and, after the full force of the waves is
broken, they sweep on inland, leaving the debris with which they are
loaded, heaped and strewn through the forests, or lodged in the very
tree-tops. The most powerful roots of the largest trees cannot with
stand the porordca, for the ground itself is torn up to great depths in
many places, and carried away by the flood to make bars, add to old
islands, or build up new ones. Before seeing these evidences of its
devastation, I had heard what I considered very extravagant stories
of the destructive power of the porordca; but, after seeing them,
doubt was no longer possible. The lower or northern ends of the
islands of Bailique and Porquinhos seemed to feel the force of the
waves at the time of my visit more than any of the other islands on
the south-east side of the river, while on the northern side the forest
was wrecked, and the banks washed out far above Ilha Nova.
The explanation of this phenomenon, as given by Condamine, ap
pears to be the correct one ; that is, that it is due to the incoming
tides meeting resistance, in the form of immense sand-bars in some
places, and narrow channels in others.1
1 Professor Hartt attributes the porordca of the Rio Mearim in Maranhao to the form of the
channel. It cannot be questioned that the form of the channel may modify, and does modify,
the force with which the surf strikes ihe shore ; but the single fact of its great violence along the
shores between the Araguary and Cape North, where the whole coast is exposed to the open
sea save for the protection offered by shallows, is sumcient to show that form of channel alone is
not its sole cause. The form of tho channel doubtless causes what Bernardino de Souza calls
the ' diving ' of the porordca on the Rio Guama.

Most persons who mention the porordca, say that it breaks as far
up the Amazon as Macapa ; and, indeed, the people of Macapa them
selves often refer to the rapid cutting-away of the river-banks near
their city as the work of the porordca. It is true that these banks are
being rapidly cut down ; and it is even a common thing to see, in this
part of the country, the stilted houses, — the floors being nearly two
metres from the ground, — that were originally built one, two, or
three hundred feet from the water, gradually encroached upon until
they fall into the stream. A portion of the old fort at Macapa was,
at the time of my visit, about to fall, on account of the land upon
which it was built being washed away ; but all this is the work of a
rapid current, for the surf of the porordca does not reach Macapa,
though it may reach a little farther
west than I have represented on
the map. Moreover, there is a
marked difference in character be
tween the washing done by the
porordca and that done by the or
dinary river or tide current. The
latter works from below, and, by
undermining and softening the section of a falling bank on the
0 AMAZON.
bank, causes what is known through
the Amazon valley as terras cahidas, or fallen banks. The land falls
into the stream in sections of various widths, and not infrequently
these form temporary terraces miles in length. These terras^ cahidas
are most common and most extensive on the upper Amazon during
high water ; but they may be seen on a small scale at various places
through the valley.1 The accompanying diagram and sketch were
made near Mazagao, on the lower Amazon. From this it is clear
that the work of destruction goes on entirely below the surface.
With the porordca, on the contrary, the water is dashed fairly
against the banks, and the earth is washed away from above as well
as from below, and the shore is left perfectly clean. The depth to
which the banks are cut shows that this disturbance is also a pro
found one ; so much so, indeed, that on the north-west side of Por-
quinhos the deepest place in the channel of the river was, in 1881,
close to this island, where the action of the porordca was most
violent. » For a good description of the terras cahidas see The Naturalist on the Amazon, by Bates,
5th ed.,p,249.

All through this region the porordca is largely instrumental in the
rapid and marked changes that are constantly going on. The water
of the Amazon is notoriously muddy, and, as would naturally be
expected, these disturbances in comparatively shallow places make it
much more so, and fill
it with all the sedi
ment it can possibly
carry. Even when I
-^""" entered the Araguary,
SHORE 2 M. HIGH, WASHED BY THE POROROCA, FORMERLY & timP wlldl there
COVEliED WITH FOREST. was the least possible
tidal disturbance, the water near the mouth of this stream was
so muddy, that a thick sediment would settle in the bottom of a
vessel of it left standing a single minute ; though the water of the
Araguary proper, as far down as the Veados, is of a clear dark color.
But the work of tearing down and that of building up is equally rapid,
and the vegetable world takes quick possession of what the sea offers
it; and, while some islands are being torn away, others are being
built up, old channels being filled, islands joined to the mainland, and
promontories built out. To the north-west of Faustinho is an island
known as the Ilha Nova ('new island'), about ten miles long by
about three wide, when I saw it, and which, I was assured by several
trustworthjr persons, did, not exist six years before. In 1881 it was
covered by a dense forest. The young plants were sprouting at the
water's edge, those behind a little taller, and so on ; so that the vege
tation sloped upward and back to a forest from twenty to thirty metres
high in the middle of the island.1 Again : on the southern side of the
mouth of the Araguarj' was a point of land nearly or quite six miles
in length, and covered with vegetation, from young shoots to bushes
six metres high. I was told, that, one year before, this was nothing
more than a sand-bar, without a sign of vegetation on it. The west
ern end of the Island of Porquinhos was once known as Ilha Franco ;
but the channel that separated it from the Porquinhos has been filled
up gradually, and the two islands are now one, though the upper end
of it is still known as Franco. The point in the mouth of the
Araguary known as the Ilha dos Veados (' deer island '), was, at the
time of my visit, fast being joined to the mainland. A couple of years
before, boats navigating the Araguary passed through the channel on
1 The plants growing upon this newly formed land are all of one kind. They are called
Ciriuba, or A7n?t6a,by the inhabitants, and belong to the family Verbenaccae, genus Avicennia.

9
the south side of the island. In 1881 it was no longer navigable, and
the Veados was rapidly being made part of the right bank of the
river. Owing to this shifting of material, the pilots never know where to
find the entrance to the Araguary River. One week the channel may
be two fathoms deep on the north side, and the next it maj' be in the
middle ; or it may have disappeared altogether, leaving the river-bed
perfectly flat, with only one fathom of water across the whole mouth.
The bar was in this last-mentioned condition when I passed over it in
1881. At this time another bar extended eastward from the eastern
end of Bailique, while a little farther out was another just south of
the same line, as I have indicated on the map. The shifting nature
of the sand-bars about the mouth of the Araguary renders it unsafe
for vessels drawing more than one fathom to enter this river, except
at high tides. But, as high tides arid the porordca come at the same
time, only light-draught steamers can enter by waiting well outside
the bar until the force of the porordca is spent.1
With the few canoes or small sailing-vessels that enter this stream
(probably less than half a dozen a year) , it is the custom to come
down past Bailique with the outgoing tide, and to anchor north of the
bar that projects from the southern side of the Araguary, and there to
await the turn of the tide to ascend the latter river. Care is always
taken to pass this point when the tides are least perceptible.
Although the porordca breaks as far up the Araguary as midway
between the Veados and the entrance to the Apureminho, its violence
seems to be checked by the narrowing of the stream below the Vea
dos, by the turns in the river, and by the vegetation along the banks.
This vegetation is of the kind against which it seems to be least
effective, namely, bamboos. They grow next the stream from near
the mouth to the foot of the falls above the colony, and for much of
the distance form a fringe to the heavy, majestic forest behind them,
than which nothing could be more strikingly beautiful. The clusters
next the stream droop over till their graceful plumes touch the sur
face of the water, and, as the plants grow older, they droop lower,
» Probably the only steamers that have entered the Araguary have been Brazilian men-of-
war of light draught. But in 1881 there was nothing to take a steamer, however small, into this
region; for although the forests below the falls contain an abundance of rubber trees, and
although cacao-trees form extensive forests, there was at that time next to no population on the
stream, while the malaria and the mosquitoes made it almost impossible to live there. Indeed,
this region, is noted for being the moBt unhealthful on the lower Amazonas. Some rubber is
gathered above the falls, but it is carried overland from Porto Grande to the Rio Matap^, and
thence by canoes to Macapa.

10
until the stream is filled with a yielding mesh of canes. I measured
a number of these bamboos ; and the longer ones, taken at random,
were from twenty to twenty-five metres in length, and from seven to
ten centimetres in diameter. A more effectual protection against the
porordca could hardly be devised.
On Bailique and Brigue I found the forests very different from any
I had hitherto seen in the tropics. These islands, like all the others
in this part of the country, are flooded at high tide during part of the
year, and as a consequence they are very like great banks of mud
covered with the rankest kind of vegetation. This vegetation varies
with the locality. All around the borders, Brigue is fringed with tall-
assai palms, bamboos, and various kinds of tall trees, all of which are
hung with a dense drapery of sipos (lianes) and vines, which form an
almost impenetrable covering. Inside of this are several palms, the
most common being the ubussu (Matricaria saccifera) . The next in
order are the murumuru (Astrocaryum miirumurii), urucury (Attelea
excelsa, the nut of which is used for smoking rubber), and ubim
(Geonoma) . But, unlike most tropical forests, this one has very little
or no undergrowth, except upon the borders. Most of the ground
was under from one to six inches of water, while the exposed places
were covered with fine sediment deposited bj- the standing muddy
waters of the Amazon. I walked several miles through this forest
without finding any palms except the ones mentioned. The little
ground above water was covered with the tracks of deer, pacas,
cutias, and of many kinds of birds, mostly waders ; but the death
like stillness was unbroken, save for the little crabs that climbed
vacantly about the fallen palm-leaves, or fished idly in the mud for a
living. This half-land and half-water condition of the country is common
not only in the immediate vicinity of the mouth of the river, but
through a verj' large part of the valley of the Amazon, and is one of
the most impressive features of this wonderful region. But, instead
of adding to what has already been written upon this subject, I will
quote a few words from two writers whose descriptions are entirely
trustworthy : ' All that we hear or read of the extent of the Ama
zons and its tributaries fails to give an idea of its immensity as a
whole. One must float for months upon its surface in order to under
stand how fully water has the mastery over land along its borders.
Its watery labyrinth is rather a fresh-water ocean, cut up and divided

11
by land, than a network of rivers. Indeed, this whole valley is an
aquatic, not a terrestrial basin.' 1
' This belt . . . cannot be called either land or sea, island or archi
pelago. It is a veritable labyrinth of streams, canals, gulfs, islands,
and lakes, combined in such a fashion as to impress one as the caprice
of man rather than as the work of nature.' 2
This vast expanse of muddy water, bearing out into the ocean im
mense quantities of sediment ; the porordca, breaking so violently on
the shores, and carrying away the coarser material to the open sea,
and burying uprooted forests beneath newly formed land ; the rank
vegetation of islands and varzea rapidly growing and as rapidly decay
ing in this most humid of climates ; the whole country, submerged for
a considerable part of the year by the" floods of the Amazon, — im
press one with the probability of such phenomena having been in past
ages, and still being, geological agents ^worthy of study and consider
ation. Across the mouth of the Amazon, a distance of two hundred
miles, and for four hundred miles out at sea, and swept northward by
ocean-currents, beds of sandstone and shale are being rapidly deposited'
from material, some of which is transported all the way from the
Andes, while in many places dense tropical forests are being slowly
buried beneath the fine sediment thrown down by the muddy waters
of the great river. NOTE.
So many random and erroneous statements concerning the porordca
have been made by writers upon Brazil, that I take this occasion to
refer to and correct some of the most glaring of them.
One authority who visited the Amazon region in 1846 s has made
waj- with it altogether, and says that ' no one knows of such terrible
phenomena nowadays,' although he ' inquired of several persons ac
customed to piloting in the main channel, and of others long resident
in the city ' of Para. But, with the exception of a very few who have
business-relations in that direction, the people of the city of Para, as
a rule, know as little of the northern mouth of the Amazon as they do
of the mouth of the Nile. And no wonder ; for the Araguary region
cannot be considered an attractive one in any respect, while the rela-
i A journey in Brazil, by Professor and Mrs. Louis Agassiz, p. 256.
2 Major Joao Martins da Silva Coutinho in the Bulletin de la societe de geographie (October
1867), p. 330.
a A voyage up the Amazon, by William H. Edwards, p. 240.

12
tions of the Paraenses with the outside world are all through the Para
River, which is the main channel, and the only one used nowadays by
vessels visiting the Amazon, whether stopping at Para, or going far
ther up the valley.
One writer tells how ships coming up the Amazon to Para avoid the
porordca;1 another says it rises suddenly along the whole width of
the Amazon ; 2 while a third says it is washing away the shore at the
Salinas lighthouse, south-east of the mouth of the Para, River.8 In reply
to all this, I have only to repeat that the porordca proper is confined
to the northern mouth of the Amazon in the vicinity of the Rio Ara-
guarj-. It is well known that the tide is felt as far up the Amazon as Obi-
dos. Mr. Belmar has erroneously attributed this to the porordca.
One authority, in describing this phenomenon, represents the waves
as breaking upon the rocks.4 I can say from personal observation,
that there is not a rock to be seen from a short distance below Macapa,
to near the colony on the Araguary. I cannot speak positively of
what may be found in the vicinity of Cape North, but I very much
doubt there being many rocks exposed there, if any at all.
All that has been written upon this subject b}^ persons having seen
the phenomenon, or visited the theatre of its action in Brazil, is limited
to the notes of Condamine on the great porordca of the Amazon and
Araguaiy,6 to those of Bernardino de Souza6 and Mr. Wallace7 on
the small one of the Rio Guama. Dr. Marques also gives something
regarding its occurrence on the Rio Mearim, in the province of
Maranhao.5 1 Voyage aux Provinces Bresiliennes de l'Amazonie, par A. de Belmar, pp. 69-71.
2 The Andes and the Amazon, by James Orton, p. 725.
8 Bulletin de la socicte de geographie, November, 1871, p. 315.
* " . . Elle Baute sur les hauts fonds, secoue sa longue et blanche criniere que la brise em-
porte comme un nuage de neige, s'abat et se releve avec plus de fareur sur lea rockers qu'elle
senible pulveriser, sur les lies qu'elle recouvre. Rien ne lui resiste ; les arbres seculaires sont
coupes, tourdus et roules dans les flots au milieu dee rochers," etc. — Bui. de la soc. de gdog.
(November, 1871), p. 322.
i Voyage fait dans l'interieur de l'Amerique Meridionale, par M. de la Condamine (Paris,
1745), pp. 193-195.
o Lembrancas e Curiosidades do Valle do Amazonas, pelo Conego Francisco Bernardino de
Souza (Para, 1873) , pp. 126, 127.
' The Amazon and Rio Negro, by Alfred R. Wallace, pp. 114 et seq., where it is spoken of
as a ' pirordca.'
8 Diccionario da Provincia do Maranhao, por Cezar Augusto Marques (Maranhao, 1870), pp.
385, 386.

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