The Amazon, flowing southward across Brazil in the broad equatorial part of South America, has the world's largest drainage basin, more than 7 million km2 (2.7 million mi2), or nearly 5% of the world's total land area. It carries nearly 20% of the Earth's total water discharge to the ocean in a flow so powerful that it perceptibly dilutes the ocean water of the Atlantic Ocean 160 km (100 mi) beyond the coastline. The Amazon is generally considered the world's second-longest river, after the Nile, with a length of about 6,450 km (4,000 mi). Its source, first identified in 1971 and confirmed in 1998 99, is a small stream fed by the snows of Nevado Mismi, a mountain in southern Peru, that flows into the Apurimac River. The exact distance to its mouth is impossible to determine, however, because the mouth, with its many islands, is so indistinct.

The River's Course and Environment

The Amazon's headstreams form in the Peruvian Andes little more than 160 km (100 mi) from the Pacific Ocean. In 1541 the Spanish explorer Francisco de Orellana began European exploration there, descending the river to the Atlantic. He is variously reported to have imagined, sighted, or been attacked by female warriors. In any event, he gave the river its name, which refers to the Amazons of Greek mythology. Most of the river's drainage basin lies east of the Andes. It is composed of low plains less than 150 m (500 ft) above sea level, strips of floodplain alongside the channels, and broken higher ground in the upper reaches of its many tributaries, to both the north and the south.

The Amazon's mouth is an estuary, 240 km (150 mi) wide at the coast and studded with low muddy islands. These represent the beginnings of a delta formed 5,000 years ago when melting glaciers created an ocean level higher than it is today. A submerged delta built during periods of glacial maximum and low ocean level stands on the continental shelf.

The estuary's tidal range reaches 5.7 m (18.7 ft), and a tidal bore, or wave, occurs from time to time. Ocean tides are felt as far as Obidos, 960 km (600 mi) inland, where the river's discharge is an average 180,000 m3/sec (6,356,650 ft3/sec) and 283,000 m3/sec (about 10 million ft3/sec) at bank-full stage. This enormous volume is a result of the humid tropical climate that characterizes most of the basin: the mean annual temperature is 26° C (79° F); precipitation, 2,000 mm (79 in). The climate sustains the world's largest rain forest, or selva, and promotes intensive land weathering. The suspended load of silt and clay is 350 million metric tons per year (386 million U.S. tons per year) and resembles that of the midlatitude Mississippi River. Oceangoing ships can travel as far as Manaus, whereas vessels drawing 6 m (20 ft) can reach Iquitos in Peru, 3,700 km (2,300 mi) inland. Of the chief tributaries the Negro, Japurá, Putumayo, Napo, Ucayli, Juruá, and Purus are also navigable for long distances. Rivers remain the chief means of transport, but airstrips and highways are opening the Amazon Basin to development.

Resources and Development

The Amazon Basin is home to more than 2 million insect species, 100,000 plants, 2,000 species of fish, and 600 mammals, many of which are found nowhere else in the world. The basin also has huge reserves of bauxite, gold, manganese, nickel, copper, tin, and timber and vast hydroelectric potential. In 1978 the eight Amazon Basin nations signed the Treaty of Amazon Cooperation (Amazon Pact), agreeing to share in the region's resources.

In recent years thousands of landless Brazilian peasants have flocked to the sparsely populated region to build homesteads, leading to clashes between farmers and ranchers, settlers and large-scale developers, and newcomers and indigenous aboriginal groups (chiefly slash-and-burn cultivators and fishing communities). Many scientists fear that unregulated development will have irreversible effects on the fragile Amazon Basin ecosystem; some contend that the vast fires associated with development (an area one and one-half times that of New York State burned in 1987 alone) are contributing to global warming. The dangers to the forest are still strong, especially at the edges. Deforestation in 1994 95 was the worst ever recorded  about 29,000 km2 (11,200 mi2) of rain forest were destroyed, despite international pressures and efforts by the Brazilian government to stop the destruction. The rate of deforestation decreased in 1996 and 1997 but later increased to a five-year high of 18,226 km2 (7,037 mi2) in 2000 before dropping to 15,787 km2 (6,095 mi2) in 2001. Subsequent research indicated that the deforestation rate might actually be double what was indicated by satellite monitoring, which did not record deforestation that did not totally eliminate tree cover. Many experts advocate tourism, mining, and the responsible harvesting of forest products as alternative means of bringing economic development to the region. In 2000 a coalition consisting of the Global Environment Facility, the World Wildlife Fund, and the Brazilian government announced a program that would set aside at least 10% of the Brazilian Amazon rain forest in sustainable development reserves over a 10-year period, based on their biological diversity. That same year, however, the Brazilian government announced a program to repair and pave four highways in the region and to construct hydroelectric plants and other projects there. Scientists feared that the program, called Advance Brazil, would open largely untouched rain-forest areas in the south and east to development that could lead to the destruction of more than one-third of the Brazilian Amazon rain forest within 20 years. In January 2001 the Brazilian government said that it would be willing to make changes to the program if it was found to damage the environment.

George Dury

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