In contrast to the Andes, which rose to elevations of nearly 7,000 metres (22,966 ft) in a relatively recent epoch and inverted the Amazon's direction of flow from westward to eastward, Brazil's geological formation is very old. Precambrian crystalline shields cover 36% of the territory, especially its central area. The principal mountain ranges average elevations just under 2,000 metres (6,562 ft). The Serra do Mar Range hugs the Atlantic coast, and the Serra do Espinhaço Range, the largest in area, extends through the south-central part of the country. The highest mountains are in the Tumucumaque, Pacaraima, and Imeri ranges, among others, which traverse the northern border with the Guianas and Venezuela.
In addition to mountain ranges (about 0.5% of the country is above 1,200 m/3,937 ft), Brazil's Central Highlands include a vast central plateau (Planalto Central). The plateau's uneven terrain has an average elevation of 1,000 metres (3,281 ft). The rest of the territory is made up primarily of sedimentary basins, the largest of which is drained by the Amazon and its tributaries. Of the total territory, 41% averages less than 200 metres (656 ft) in elevation. The coastal zone is noted for thousands of kilometers of tropical beaches interspersed with mangroves, lagoons, and dunes, as well as numerous coral reefs.
Brazil has one of the world's most extensive river systems, with eight major drainage basins, all of which drain into the Atlantic Ocean. Two of these basins—the Amazon and Tocantins-Araguaia account for more than half the total drainage area. The largest river system in Brazil is the Amazon, which originates in the Andes and receives tributaries from a basin that covers 45.7% of the country, principally the north and west. The main Amazon river system is the Amazonas-Solimões-Ucayali axis (the 6,762-kilometre (4,202 mi)-long Ucayali is a Peruvian tributary), flowing from west to east. Through the Amazon Basin flows one-fifth of the world's fresh water. A total of 3,615 kilometres (2,246 mi) of the Amazon are in Brazilian territory. Over this distance, the waters decline only about 100 metres (330 ft). The major tributaries on the southern side are, from west to east, the Javari, Juruá, Purus (all three of which flow into the western section of the Amazon called the Solimões), Madeira, Tapajós, Xingu, and Tocantins. On the northern side, the largest tributaries are the Branco, Japurá, Jari, and Rio Negro. The above-mentioned tributaries carry more water than the Mississippi (its discharge is less than one-tenth that of the Amazon). The Amazon and some of its tributaries, called "white" rivers, bear rich sediments and hydrobiological elements. The black-white and clear rivers—such as the Negro, Tapajós, and Xingu—have clear (greenish) or dark water with few nutrients and little sediment.
The major river system in the Northeast is the Rio São Francisco, which flows 1,609 kilometres (1,000 mi) northeast from the south-central region. Its basin covers 7.6% of the national territory. Only 277 kilometres (172 mi) of the lower river are navigable for oceangoing ships. The Paraná system covers 14.5% of the country. The Paraná flows south among the Río de la Plata Basin, reaching the Atlantic between Argentina and Uruguay. The headwaters of the Paraguai, the Paraná's major eastern tributary, constitute the Pantanal, the largest contiguous wetlands in the world, covering as much as 230,000 square kilometres (89,000 sq mi).
Below their descent from the highlands, many of the tributaries of the Amazon are navigable. Upstream, they generally have rapids or waterfalls, and boats and barges also must face sandbars, trees, and other obstacles. Nevertheless, the Amazon is navigable by oceangoing vessels as far as 3,885 kilometres (2,414 mi) upstream, reaching Iquitos in Peru. The Amazon river system was the principal means of access until new roads became more important hydroelectric projects are Itaipu, in Paraná, with 12,600 MW; Tucuruí, in Pará, with 7,746 MW; and Paulo Afonso, in Bahia, with 3,986 MW.
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