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 Mountains, 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. The main lowland is the vast Amazon Basin in the equatorial part of the continent; it is drained by the Amazon River, the world's second longest river. The Orinoco River drains a lowland in the north; 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 (6,960 m/22,834 ft) is atop Aconcagua in western Argentina, 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 and Guiana highlands of the east and northeast. 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 Paleozoic 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 landmass 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 1.6 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 continues all up and down the continent's western rim. 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.

Natural Regions

Rising abruptly from the northwestern 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 consists of two or three parallel axes of mountains, known as cordilleras, or ranges. In southwestern Bolivia and southern Peru, a region of large intermontane plateaus called the Altiplano separates the ranges. In Peru and Argentina the ranges are separated by relatively narrow but deep valleys. Among the two dozen peaks that exceed an elevation of 17,000 ft (equivalent to 5,182 m) are a number of active volcanoes located in south central Chile, southern Peru and Bolivia, and Ecuador.

The vast uplands of Guiana, in the northeast, and of Brazil, in the east, have rolling to hilly surfaces, with broad plateaus and high mesas. The plateaus are higher and less broad 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 (see Patagonia). Although soils here are generally fertile, climatic constraints limit their agricultural usefulness.

The northernmost of the continent's principal lowland areas is the Orinoco Basin, which includes the Llanos—a region of alluvial plains and low mesas—and a vast system of valleys that converge toward 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.

C.

Drainage and Water Resources

The greater part of South America is drained to the Atlantic Ocean by three river systems: the Amazon, Orinoco, and Paraguay-Paraná. Each of these large rivers also provides access to the interior. The smaller São Francisco River drains northeastern Brazil. Numerous lesser rivers drain the Caribbean and Pacific flanks of the Andes. The most important of these is the Magdalena River and its tributary, the Cauca River. This system, which drains north through Andean valleys in western Colombia to empty into the Caribbean Sea, has also provided a traditional access route to the interior. Scores of short Andean streams have sustained agriculture for centuries in Ecuador, Peru, Chile, and northwestern Argentina. Considerable hydroelectric power potential exists in the streams of the Andes and in those of the Guiana and Brazilian Highlands. The Mantaro Valley hydroelectric scheme in the Andes of Peru provides most of Lima's electricity.

South America has few large lakes. Many of the large permanent lakes are situated at relatively high elevations in the Andes. Among the largest are Lake Titicaca and Lake Poopó in Bolivia; Buenos Aires, Argentino, and Nahuel Huapí lakes in Argentina; and Lake Valencia in Venezuela.

D.

Climate

South America is dominated by relatively warm climatic regimes. Spanning nearly the entire continent along the equator is a belt of humid tropical climate that grades to the north and south into broad zones where the length of the rainy season and the amount of rainfall diminish. These zones have wet summers and dry winters and are subject to prolonged droughts. Droughts are a particularly serious problem in northeastern Brazil and along the northern coast of Venezuela and Colombia. The areas of rainy tropical and tropical wet-dry climate extend along the Pacific coast of Colombia and Ecuador but are marked by a sharp southern transition into the arid climate of coastal Peru and northern Chile. In the northern half of South America only the Andes region has a cool climate. Temperatures decrease with increasing elevation, so that the tropical climate of the lowlands and lower slopes changes to subtropical and temperate climates at intermediate elevations, and finally to cold alpine climate at the mountain crests.

South of the tropic of Capricorn, South America has cool to cold winters and cool to warm summers. Southern Chile receives heavy precipitation, because of the cyclonic storms that move off the Pacific Ocean from the west. The storm frequency, greatest in winter, diminishes northward through Chile, resulting in a zone of Mediterranean-like climate, with mild, wet winters and warm, dry summers. This zone is bordered by desert, which extends along the coast as far north as Ecuador. Included in this region is the Atacama Desert, one of the driest places in the world. Subhumid and arid conditions prevail to the east of the southern Andes. In the Pampas and southern Brazilian Highlands, however, summers tend to be humid, and in the winter cyclonic storms may penetrate, bringing rain and chilly weather. Snow occasionally falls over the highlands, and frosts may spread north toward the tropic of Capricorn, causing extensive damage to crops.

E.

Vegetation

The vegetation zones of South America correspond closely with the climatic zones. The areas of wet tropical climate have a dense cover of rain forest, or selva. The largest forest area in the world, this rain forest covers much of equatorial South America, including the Brazilian coast and the lower slopes of the Andes, and contains tropical hardwoods, palms, tree ferns, bamboos, and lianas. Open forests and brushlands are found in the areas of winter drought chiefly on the Venezuelan coast, in northeastern Brazil, and on the Gran Chaco. Between these drier areas and the rain forest are zones of tall grass (savannas, or campos) and of scrub and grass (campos cerrados). Mixed (containing both deciduous and evergreen trees) and deciduous forests occur in southern Brazil and along the slopes of the Andes. In Brazil the forest grades, to the south, into areas of rolling prairie interrupted by wooded hills. The Gran Chaco is characterized by grassy plains and open thorn scrub forest. The flat Pampas of east central Argentina is the largest midlatitude grassland of South America. To the south a zone of scrub steppe (monte) marks the transition to the low brush and bunch grass that cover the drier and cooler Patagonia region. Along the Pacific coast, the vegetation grades northward from forest to open woodland, to shrubs and grass in central Chile, and eventually to the scrub and desert vegetation that prevails into northern Peru and up to the mountain flanks.

F.

Animals

South America, Central America, the lowlands of Mexico, and the West Indies may be classified as a single zoogeographic region usually called the Neotropical Region. Fauna is characterized by variety and a singular lack of affinity with the fauna of other continents, including North America north of the Mexican Plateau. Found throughout are families of mammals absolutely confined to the region, including two unique species of monkey, bloodsucking bats, and many unusual rodents. The region has only one kind of bear, the spectacled bear; no horses or related animals, aside from one species of tapir; and no ruminants, except lamoids (members of the camel family), which include alpacas, llamas, and vicuñas. Also characteristic of the continent are jaguar, peccary, giant anteater, and coati. Birds display still greater isolation and singularity. About 23 families and about 600 genera of exclusively Neotropical birds occur, as well as the greater part of other important families, such as those of the hummingbirds (500 species), tanagers, and macaws, together with a great variety of sea fowl. The largest birds include the rhea, condor, and flamingo. Reptiles include boas and anacondas; iguanas, caimans, and crocodiles are found in many areas. Freshwater fish are varied and abundant. Regional exclusiveness also characterizes insects and other invertebrates. On the whole, South American fauna is more local and distinct than that of any continent other than Australia; probably more than four-fifths of its species are restricted to its zoogeographic boundaries. The Galápagos Islands are the habitat of reptiles and birds that are unknown elsewhere, including the Galápagos giant tortoise, Darwin's finches, and the Galápagos penguin.

G.

Mineral Resources

South America has diverse mineral resources, many of which have not been extensively exploited. Mineral deposits are widely distributed, but certain areas of the continent are particularly renowned for their wealth. In the Andes placer gold has been worked in various areas since before the colonial era. The mountains between central Peru and southern Bolivia produced silver and mercury in the colonial era, and industrial minerals such as copper, tin, lead, and zinc today. Copper is worked at large deposits in northern and central Chile and in central and southern Peru. A highly mineralized area containing bauxite, iron ore, and gold lies between Ciudad Bolívar and northern Suriname, near the northern margin of the Guiana Highlands. In east central Brazil rich gold and diamond strikes occurred in the colonial era, some of these mines are still producing. Although South America is a major producer of rare metals, the large reserves of high-grade iron ore and smaller reserves of bauxite are more important to the emerging industrial power of the continent.

South America is lacking in large coal reserves. Coal is found in scattered and relatively small deposits in the Andes and in southern Brazil. Coal has been an important fuel for industry and transportation primarily in Chile, Colombia, and Brazil. Petroleum, however, is widely distributed. Most of the continent's reserves of petroleum and natural gas lie in structural basins located mostly along the eastern margins of and in the Andes, from Venezuela to Tierra del Fuego. The largest known fields are in the Lake Maracaibo area of Venezuela. Other deposits occur in northern Colombia, Ecuador and Peru, south of the Andes in eastern and central Venezuela, and just east of the mountains in Colombia, Ecuador, Peru, Bolivia, Argentina, and Chile.