I | INTRODUCTION |
Amazon
(river) (Portuguese and Spanish Amazonas), river in northern South
America, largely in Brazil, ranked as the largest in the world in terms of
watershed area, number of tributaries, and volume of water discharged. Measuring
6,400 km (4,000 mi) from source to mouth, it is second in length only to the
Nile among the rivers of the world. With its hundreds of tributaries, the Amazon
drains a territory of more than 7 million sq km (2.7 million sq mi), roughly
half of which is in Brazil; the rest is in Peru, Ecuador, Bolivia, and
Venezuela. It is estimated that the Amazon discharges between 34 million and 121
million liters (9 million and 32 million gallons) of water per second and
deposits a daily average of 3 million tons of sediment near its mouth. The
annual outflow from the river accounts for one-fifth of all the fresh water that
drains into the oceans of the world. The outpouring of water and sediment is so
vast that the salt content and color of the Atlantic Ocean are altered for a
distance of about 320 km (about 200 mi) from the mouth of the river.
II | COURSE AND PHYSICAL ENVIRONMENT |
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.
III | EXPLORATION AND DEVELOPMENT |
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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