South America

I

Introduction

South America, the fourth-largest of the Earth's seven continents (after Asia, Africa, and North America), occupying about 17,819,100 sq km (6,880,000 sq mi), or about 12 per cent of the Earth's land surface. It lies across the equator and tropic of Capricorn and is joined by the Isthmus of Panama, on the north, to Central and North America. The continent extends about 7,400 km (4,600 mi) from the Caribbean Sea on the north to Cape Horn on the south, and it spans some 4,830 km (3,000 mi) between its easternmost point, Cabo de São Roque on the Atlantic Ocean, and Punta de Pariñas on the Pacific Ocean.

The continent comprises ten Latin nations (Argentina, Bolivia, Brazil, Chile, Colombia, Ecuador, Paraguay, Peru, Uruguay, and Venezuela), Guyana (formerly a British dependency), Suriname (formerly a Dutch dependency), and French Guiana (an overseas department of France). Located at great distances from the continent in the Pacific Ocean are several territories of South American republics: the Juan Fernández Islands and Easter Island (both Chilean territories) and also the Galápagos Islands (Ecuadorian). Nearer the coast, in the Atlantic Ocean, is the Fernando de Noronha Archipelago, which is a Brazilian territory, and, farther south, the British dependency of the Falkland Islands (Islas Malvinas), which is also claimed by Argentina. The coastline of South America is relatively regular except in the extreme south and south-west, where it is indented by numerous fiords.

II

The Natural Environment

South America consists of four upland provinces, extending inland from the coasts, and, between them, three lowland provinces. The northern and western fringes are dominated by the Andes, the second highest mountain range in the world. Most of the eastern coast is fringed by the broader—and generally less elevated—highland areas of the Guiana and Brazilian massifs and the Patagonian Plateau (see Patagonia). The major lowland is the vast Amazon Basin in the equatorial part of the continent; it is drained by the Amazon, the world's second longest river. The smaller northern lowland counterpart to the Amazon Basin is drained by the Orinoco River; to the south lies the Paraguay-Paraná basin. The lowest point in South America (40 m/131 ft below sea level) is on Península Valdés in eastern Argentina, and the greatest elevation (6,959 m/22,831 ft) is at Aconcagua in western Argentina, which is the highest peak in the western hemisphere.

A

Geological History

The oldest and most stable structural element of the continent is the shield area of the Brazilian Highlands and Guiana Highlands of the east and north-east. It comprises a Precambrian (before 570 million years ago) complex of igneous and metamorphic rocks. In most places the shield is overlaid by sedimentary rocks, mostly of Palaeozoic age (570 million to 225 million years ago), although some areas of younger basalts occur, notably in southern Brazil. Fossils found in the Brazilian Highlands offer evidence of continental drift, indicating that in the Permian period the continent was linked to Gondwanaland, a great land mass incorporating Africa and Asia.

The complex that underlies the Patagonian Plateau is largely mantled by sediments deposited in the Mesozoic era (225 million to 65 million years ago) and Tertiary period (65 million to 2.5 million years ago) and by basalts of recent formation.

Material eroded from the old shield areas contributed to the thick deposits of sediments in the surrounding seas. These sedimentary formations were uplifted repeatedly in the Mesozoic era to form the coast ranges of Chile and southern Peru and the higher and more extensive Andes. This mountain-building process, which continued through the Tertiary period, was accompanied by intrusions of magma (molten rock) and by the formation of volcanoes. Volcanic and seismic activity continue all up and down the continent's western rim, as the Pacific plate forces its way beneath (subducts) the South American one (see Plate Tectonics). The glaciers of the southernmost Andes are remnants of the great ages of glaciation of the Quaternary period (beginning 2.5 million years ago). The erosion of the highlands continues to contribute sediments to surrounding lowlands.

B

Physiographic Regions

Rising abruptly from the north-western and western coasts of the continent are the Andes. They consist of a single chain in Venezuela (in the north) and through much of Chile and Argentina (in the south), but the central part of the mountain system is marked by two or three parallel axes of mountains, known as cordilleras, or ranges. In western Bolivia large intermontane plateaux separate the ranges. Among the two dozen peaks that exceed 5,182 m (17,000 ft) in elevation are a number of active volcanoes located in south central Chile, southern Peru and Bolivia, and Ecuador.

The vast uplands of Guiana in the north-east and of Brazil in the east have rolling to knobby surfaces, with broad tablelands and high mesas. The tablelands are higher and less extensive in the highlands of Guiana. In the Brazilian Highlands, the greatest relief occurs in mountains that lie along the eastern coast, in many places rising abruptly from the sea. In general, the rocks of these uplands have weathered into infertile, reddish soils. Fertile soils derived from basaltic rocks are found in many valleys, however. To the south is the less elevated and relatively flat Patagonian Plateau. Although soils here are generally fertile, climatic constraints limit their agricultural usefulness.

The northernmost of the continent's major areas of lowland is the Orinoco Basin, which includes the Llanos—a region of alluvial plains and low mesas—and a vast system of valleys that converge towards the Amazon between the Caquetá and Madeira rivers. The Amazon basin itself is a region of slightly rolling terrain. Farther south are the shallow valleys and flat plains of the Gran Chaco and the Pampas, both of which merge with the swampy floodplains of the Paraguay and Paraná rivers.