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Amazon River World's second longest river, c.3,900 mi (6,280 km) long, formed by the junction in N Peru's Andes Mts. of two major headstreams, the Ucayali and the shorter Maran. It flows across N Brazil before entering the Atlantic Ocean near Belm.
The Amazon carries more water than any other river in the world. The drainage basin is enormous (c.2,500,000 sq mi/6,475,000 sq km; c.35% of South America), gathering waters from both hemispheres and covering not only most of N Brazil but also parts of Bolivia, Peru, Ecuador, Colombia, and Venezuela. For most of its course the river has an average depth of c.150 ft (50 m). The gradient of the river is very low: Manaus, c.1,000 mi (1,610 km) upstream, is only c.100 ft (30 m) higher than Belm and is an ocean port; ships with a draft of 14 ft (4 m) can reach Iquitos, Peru, c.2,300 mi (3,700 km) from the sea. Peru, Ecuador, and Colombia have international shipping rights on the Amazon. In the lowlands stretching E from the Andes is the largest rain forest (selva) in the worlda wet, green land rich in plant life. The tropical climate is tempered by the heavy rainfall (exceeding 150 in./381 cm annually in parts of the upper and lower regions) and by high relative humidity; the average temperature at Santarm, 400 mi (644 km) upriver, is 78 F (26 C).
Course
Geologically, the Amazon basin is a sediment-filled structural depression between crystalline highlands of Brazil and Guiana. The river bed (1-8 mi/1.6-12.9 km wide) is in a wide flood plain that is up to 30 mi (48 km) wide. For much of its course, the Amazon wanders in a maze of brownish channels amid countless islands, but is unobstructed by falls.
Its headstreams, however, arise cold and clear in the heights of the Andes. They descend northward before turning east to join and form the Amazon (which is, however, occasionally called the Solimes from the Brazilian border to the junction with the Rio Negro). Of the Amazon's more than 500 tributaries, the chief ones are the Negro, Japur (Caquet), Putumayo (I), and Napo, which enter from the north; and the Javari, Juru, Purs, Madeira, Tapajs, and Xing rivers, which enter from the south. The Casiquiare River, a natural canal, links the Amazon basin (through the Rio Negro) with the Orinoco basin.
Below the Xing the river reaches its delta, with many islands formed by alluvial deposit and submergence of the land. Around the largest of these, Maraj, the river splits into two large streams. The northern stream is the principal outlet and threads its way around many islands. The southern channel, called the Par River, receives the Tocantins River and has the important port of Belm. The awesome tidal bore (up to 12 ft/3.7 m high) of the Amazon is called pororoca; it travels c.500 mi (800 km) upstream. The river's immense silt-laden discharge is visible far out to sea.
Exploration and Development
The Amazon was probably first seen by Europeans in 1500 when the Spanish commander Vicente Yez Pinzn explored the lower part. Real exploration of the river came with the voyage of the Spanish explorer Francisco de Orellana down from the Napo in 1540-41; his fanciful stories of female warriors gave the river its name. Not long afterward (1559) the Spanish conquistador Pedro de Ursa led an expedition down from the Maran River. In 1637-38 the Portuguese explorer Pedro Teixeira led the voyage upstream that definitively opened the Amazon to world knowledge. The river continued to be of enormous importance to explorers and naturalists, among them Charles Darwin and Louis Agassiz.
The valley was largely left to its sparse indigenous inhabitants (mostly groups of the Guaran-Tupi linguistic stock and of meager material culture) until the mid-19th cent., when steamship service was regularly established on the river and when some settlements were made. In the late 19th and early 20th cent., the brief wild-rubber boom on the upper Amazon attracted settlers from Brazil's northeastern states, and since the 1930s Japanese immigrants have developed jute and pepper plantations. But the area still remains largely unpopulated, yielding small quantities of forest products (rubber, timber, vegetable oils, Brazil nuts, and medicinal plants) and cacao. South American countries are gradually learning to take advantage of the Amazon Valley's hydroelectric potential. The establishment of a health service (chiefly by launch) in World War II was followed by the creation of a UNESCO research institute in 1948, and several developmental programs, both governmental and private, have been set up in Brazil in recent years to foster the valley's development.
In the 1960s the Amazon region began experiencing increased economic development brought on by tax incentives and construction of the Trans-Amazon Highway, the Belm-Braslia Highway, and two rail lines. Near Manaus and Amap, factories make use of ample oil and manganese resources. In addition, a port at the Brazilian city of Macap was connected by rail in the 1950s to the inland stores of manganese. The Brazilian government implemented a poles of development policy in 1974 to plan for population increase. Since 1985 the Carajs project, centered in W Maranho, has seen the development of major iron ore deposits, the construction of a new railroad, and the initiation of forest clearance, land colonization, and urban development on an unprecedented scale. This policy has had mixed results, leading to environmental damage and to the disruption of the original inhabitants' lives. Large sections of the rain forest have been destroyed in recent years, threatening rare species of plants and contributing to the increase in the atmosphere's carbon dioxide and the consequent impact on global warming. Ucayali
River, c.1,000 mi (1,610 km) long, formed by the confluence of the Apurmac and Urubamba rivers, E Peru, and flowing generally north through a mountain and jungle wilderness to the Maran River, SW of Iquitos. It is a main headstream of the Amazon River. The Ucayali is navigable for its entire course by small craft. It is an important communications link for Iquitos. Maranon
River, c.1,000 mi (1,600 km) long, rising in Lake Lauricaucha in the Cordillera Occidental, W central Peru. It flows generally NW, then E across the Andes to join the Ucayali River in NE Peru where it forms the Amazon River; some consider the Maran to be the authentic headwater of the Amazon. It is navigable to the Pongo de Manseriche, the gorge in NW Peru through which it flows before reaching the Amazon basin. The Huallaga River is its chief tributary. Pedro de Ursa, the Spanish explorer, descended the Maran in 1560. Marajo
Island, c.150 mi (240 km) long and c.100 mi (160 km) wide, N Brazil, at the mouth of the Amazon River. It divides the river into the Amazon proper and the Par. Cattle are raised on the extensive eastern grasslands, and water buffaloes are bred in the low, swampy west. The island is famous for its prehistoric mounds, which yield handsome pottery.
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History
