When we think of a
continent, we think of ones like North America, Europe, Asia or Australia--even
Africa. But South America is a unique continent, with the central part of
Brazil and eastern Peru a huge cup-shaped basin about two-thirds the size of the
entire United States (2.7 million square miles to 2.9 million square miles of
the contiguous United States).
Overlap showing the size of the contiguous
United States overlaying the Amazon Drainage Basin
This area is
typically referred to as the Amazon Basin, or Amazon Drainage Area. It covers
30% of South America, and is 2,720,000 square miles, and is the largest
drainage area in the world, covering 25-degrees of latitude. Every year, the river
rises 30 to 40 feet and floods 140,000 square miles--which is nearly twice the size
of the state of Utah, which is the 13th largest state in the
U.S.--and empties 11,000,000 cubic feet per second into the Atlantic--which is
20% of the world’s fresh water supply.
This drainage basin
is unlike other continental areas even though it stretches over 4000 miles from
the Andes to the Atlantic. Once off the mountain range, the final 4000 miles is
about as flat as a pancake clear to the mouth of the Amazon River
Looking
West at the Amazon Delta (middle right) and the flat Amazon Basin from the
Atlantic Ocean. A flatter land covering about 2.5 million square miles cannot
be found anywhere else on Earth
According to descriptions
given from his 1870 exploration of the Amazon, Colonel George Earl Church
describes the entire Basin as being barely above sea level with “the entire region
simply an endless succession of channels, and small lakes, and swamps covered
with forest.” When the river level was
low, the banks were 6 to 10 feet above the river level--however, the river
would rise 30 to 40 feet in the wet season, flooding the banks and high ground,
and the entire Basin. “In fact the water courses pursue a sinuous path and is
everywhere interrupted by islands big and little, so much so that unless one
refers to a chart it is difficult to know when one is really passing the
mainland.”
Church went on to describe the view as he sailed up the river. “Every now
and then we passed a seringueiro's hut, or barracao,
close to the water's edge, built on posts above the rise of the river,
while in front of it were tethered one
or more canoes, the only means of transport, and indeed of refuge, when the water
is very high. These huts were simple in construction, made of poles lashed
together with bush rope, the sloping
roofs covered with broad palm leaves.”
The river flows uninterrupted for some 4000 miles, widening in places
averaging about eight miles in width and finally to 158 miles in width at the
delta. In many places the waterway is a lake-like expanse with islands in all
directions. “It is difficult for one who has
not studied this subject particularly to appreciate how many
thousands of islands, big and little,
are crowded into the lower Amazon.”
The lower Amazon is
almost nothing but water for as far as one can see and beyond
As Church described his trip: “As the river was rising we passed through
and by acres of floating grasses, weeds,
and logs, the larger masses being easily avoided. About 10 o'clock we entered
the Narrows, our channel being perhaps 300
yards wide. On either side the low lying alluvial shores were thick. For
miles we passed banks 10 or 12 feet above the water level and the impression
was that the land sloped gently up from
them. But when a break came in the forest wall, great meadows would be shown lower than the river bank. We also passed through the Narrows, that were
uninteresting and dreary. My mental picture was of an expanse of water so broad
that the shores dimly seen offered
nothing of interest.”
He described that “From February until July, the ground is underwater and
the seringaes are desereted by
everyone, and that the river rises from 30 to 40 feet, forcing huge docks to be
anchored a little way off shore, and when the river rises pay out the anchored
cables so that the dock rises with it. Goods are sent ashore from these docks
on long aerial cables, adding greatly to the cost of shipping.”
The channels in these lowlands are
called igarapes (canoe-paths) by the natives--they can be narrow, but very deep.
Everywhere one goes, the land is flooded every year and the tides sweep through
the channels every day and overflow much of the ground so that it is always
wet. Even the higher meadows are flooded in the wet season and canoes
and even small steamers can pass over them.
The marshes among the meadows are called baizas to distinguish them from the forest swamps, or ygapos, showing the continual
submergence of the land in the entire Basin."
The Amazon River
meanders for thousands of miles through this lush forest where seeds float on the
water until they can find lodging in the lowland swamps to finally sprout and
grow
This entire Amazon Basin (about the size of the contiguous United States)
even now is barely above sea level. At one time, just a few feet lower, and it
would have been submerged, forming an entire ocean--a western extension of the
Atlantic Ocean.
(See the next post, “The rising of South America,” regarding the rising
of part of the South American continent)
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