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The Amazon is the greatest river in the world by so many measures;
the volume of water it carries to the sea (approximately 20% of all
the freshwater discharge into the oceans), the area of land that
drains into it, and its length and width. It is one of the longest
rivers in the world and, depending upon who you talk to, is anywhere
between 6,259 kilometers / 3,903 miles and 6,712 kilometers / 4,195
miles long.
For the last century the length of the Amazon and the Nile Rivers
have been in a tight battle for title of world's longest river. The
exact length of the two rivers varies over time and reputable
sources disagree as to their actual length. The Nile River in Africa
is reported to be anywhere from at 5,499 kilometers / 3,437 miles to
6,690 kilometers / 4,180 miles long. But there is no question as to
which of the two great rivers carries the greater volume of water -
the Amazon River.
At its widest point the Amazon River can be 11 kilometers / 6.8
miles wide during the dry season. The area covered by the
Amazon River and its tributaries more than triples over the course
of a year. In an average dry season 110,000 square kilometers of
land are water-covered, while in the wet season the flooded area of
the Amazon Basin rises to 350,000 square kilometers. When the flood
plains and the
Amazon River Basin flood during the rainy season the Amazon River
can be up to 40 kilometers / 24.8 miles wide. Where the Amazon opens
at its estuary the river is over 325 kilometers / 202 miles wide!
The Amazon can accommodate large freighters as far upriver as the
city of
Iquitos,
Peru some 6,000 kilometers west of the River's exit point
into the Atlantic Ocean. The first European descent was made by
Francisco de Orellana in 1541; he is said to have given the river
its name after reporting battles with tribes of women, whom he
likened to the Amazons of Greek legend but the river remained little
explored until the mid 19th century. Many indigenous peoples
originally lived along the river, but they moved inland as exploring
parties and raiders sought to enslave them. The river was opened to
world shipping in the 1860s; traffic increased exponentially with
the coming of the rubber trade, which reached its height c. 1910 but
soon declined. The quantity of fresh water released to the Atlantic
Ocean is enormous: 184,000 m³ per second (6.5 million ft³/s) in the
rainy season. Indeed, the Amazon is responsible for a fifth of the
total volume of fresh water entering the oceans worldwide. It is
said that offshore of the mouth of the Amazon potable water can be
drawn from the ocean while still out of sight of the coastline, and
the salinity of the ocean is notably lower a hundred miles out to
sea. Teeming with exotic wildlife, indigenous cultures and
impressive natural wonders, the region also affords visitors a wide
variety of experiences impossible to duplicate anywhere else on
earth.
Seasonal rains give rise to extensive floods along the course of the
Amazon and its tributaries. The average depth of the river in the
height of the rainy season is 40 meters (120 feet) and the average width
can be nearly twenty-five miles. It starts to rise in November, and
increases in volume until June, then falls until the end of October.
The abundance of water in the Amazon basin is due to the fact that
much of this lies in the region below the Inter tropical convergence
zone, where rainfall is at a maximum. Also, the basin lies in the
Trade Wind zone, where moisture from the Atlantic is pushed
westwards, and eventually forced to rise over the Andes, the second
tallest mountain range on Earth, where the moist air cools and
precipitates water. This combination creates more rainfall over a
large river basin than anywhere else on the planet.
In the rainy season, the Amazon inundates the country throughout its
course to the extent of several hundred thousand square miles,
covering the flood-plain, called 'vargem'. The flood-levels are, in
some places, from 12 to 15 m (40 to 50 ft) higher than levels during
the dry season. During the flood, the level at Iquitos is 6 m (20
ft); at Tefe, it is 15 m (45 ft); near Obidos, 11 m (35 ft); and at
Para, 4 m (12 ft), above the low-water extreme seen during the dry
season.
The width of the Amazon in some places
is as much as 6 to 10 km (4 to 6 mi) from one bank to the other. At
some points, for long distances, the river divides into two main
streams with inland and lateral channels, all connected by a
complicated system of natural canals, cutting the low, flat igapo
lands, which are never more than 5 m (15 ft) above low river, into
almost numberless islands.
The waters of the Amazon support a diverse range of wildlife. Along
with the Orinoco, the river is one of the main habitats of the Boto,
also known as the Amazon River Dolphin. The largest species of river
dolphin, it can grow to lengths of up to 2.6 m.
Also present in large numbers are the notorious Piranha, carnivorous
fish which congregate in large schools, and may attack livestock and
even humans. Although many experts believe their reputation for
ferocity is unwarranted. |
