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The major headstreams of the Amazon are the
Ucayali and Marañón rivers, both of which rise in the permanent snows and
glaciers of the high Andes Mountains. Feeding the Ucayali is the Apurimac
River, the Amazon's most distant source. The headwaters of the Apurimac are
located at a glacial meltwater of Nevado Mismi, an Andean peak in southern
Peru. The Ucayali and Marañón follow parallel courses north before joining
near Nauta, Peru. From this confluence the main trunk of the Amazon flows in
a generally eastern direction to the Atlantic Ocean. The Amazon enters the
Atlantic through a broad estuary, roughly estimated at 240 km (about 150 mi)
in width.
Here delta deposits have formed a maze of islands that separate the river
into branches. The mouth of the main stream is 80 km (50 mi) wide. This
branch, known as the Pará, is separated from a smaller branch by Marajó
Island, which has an area of more than 36,000 sq km (14,000 sq mi). During
new and full moon a tidal bore, or wave front from the ocean, sweeps some
650 km (more than 400 mi) upstream at speeds in excess of 65 km/h (40 mph).
This phenomenon can cause waves 5 m (16 ft) or more in height along the
banks of the river.
The Amazon watershed includes the largest and wettest tropical plain in the
world. Heavy rains drench much of the densely forested lowland region
throughout the year but especially between January and June. Seasonal
variation in rainfall is reflected by the width, rate of flow, and discharge
volume of the river. During the months of maximum precipitation, broad areas
traversed by the Amazon are subject to severe floods. In Brazil the width of
the river ranges between 1.6 and 10 km (1 and 6 mi) at low stage but expands
to 48 km (30 mi) or more during the annual floods; the rate of flow ranges
between 2.4 and 8 km/h (1.5 and 5 mph); and the crest of the water at flood
time often rises 15 m (50 ft) above the norm. To drain the vast mass of
water, the Amazon has carved a deep bed in the plain through which it flows.
In one sector near Óbidos, Brazil, the bed is more than 91 m (300 ft) below
the average surface level of its water.
Because of its vastness, annual floods, and navigability, the Amazon is
often called the Ocean River. The total number of its tributaries is as yet
uncounted, but more than 200 are in Brazil alone. Seventeen of the largest
known tributaries are more than 1,600 km (1,000 mi) in length. The Amazon
proper is navigable to ocean liners of virtually any tonnage for two-thirds
of its course. Transatlantic ships call regularly at Manaus, nearly 1,600 km
(1,000 mi) upstream; and smaller ships can reach Iquitos, Peru,
3,700 km (2,300 mi) from the river's mouth, the farthest point from sea of
any port serving ocean traffic. River steamers of more modest tonnage can
navigate on more than 100 of the larger tributaries.
The delta region of the Amazon may have been seen by the Spanish explorer
Vicente Yáñez Pinzón in 1500, but exploration did not begin until 1541 and
1542, when an expedition led by Francisco de Orellana started down the Napo
River, in what is now Ecuador, and reached the Atlantic Ocean. Pedro
Teixeira undertook the first upstream voyage. Between October 1637 and
August 1638 he ascended the Amazon to the source of the Napo River and
crossed the Andes to Quito, Ecuador. Later, he returned by the same route.
In modern times the river has been explored by many scientific expeditions,
including that led by former American president Theodore Roosevelt in 1914
and others sponsored by the National Geographic Society and the government
of Brazil.
Some authorities believe that the river was named after the Amazons, women
warriors of Greek mythology who were thought to reside in the region. Other
scholars insist that the name is derived from the Native American word
amassona, meaning
“boat destroyer.”
Despite centuries of effort to overcome the dominance of nature, people have
made little impact on the Amazon and most of its vast drainage basin. No
bridge spans the river. Except near its mouth, the Amazon watershed
constitutes one of the most thinly populated regions in the world. Much of
the territory drained by the river system has never been thoroughly
explored. One may fly for hours over the tropical forests that cover much of
the river's floodplain and see no sign of human settlement. In many stream
valleys, Native American tribes hostile to strangers continue to live much
as they did before the arrival of the Europeans. Most commerce is narrowly
confined to the navigable sectors of the river system, although the
development of highways has improved access and goods transportation into
the area. The economy continues to be dominated by primitive agriculture,
hunting and fishing, and the gathering of various forest products.
Commercial farming, tourism, and industry play minor but growing roles in
the region, but mining and lumbering, the principal economic activities, are
increasingly important.
Large-scale development of the Amazon began in the 1980s. Such development
cleared large sections of its natural forest cover. Although the forest
quickly covers over cleared areas, the regrowth is not as diverse as the
original cover. This decline in diversity affects both animal life and the
human population, as animals and plants on which they depend become rare or
extinct and available land becomes scarce. After the area gained the
attention of international conservation groups, the Brazilian government
made efforts to monitor development and protect the Amazon's forest
resources. However, the environmental effects of development and
deforestation continue to be difficult issues as the region is developed. |
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