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The Amazon Environment |
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(Portuguese and Spanish Amazonas), river, northem 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 about 6275 km (about 3900 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 6 million sq km (2.3 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 and 121 million liters (9 and 32 million gal) 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 salinity and colour of the Atlantic Ocean are altered for a distance of about 320 km (about 200 mi) from the mouth of the river.
The major headstreams of the Amazon are the Ucayali and Maranˆun rivers, both of which rise in the permanent snows and glaciers of the high Andes Mountains and 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 Parˆh, is separated from a smaller branch by Marajˆu 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/hr (40 mph). This phenomenon often causes waves up to 5 m (16 ft) in height.
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