Physical Geography

In a general sense, South America bears some similarity to North America. High rugged mountains are in the west, lower and more rounded mountains lie to the east, and between them are lowlands and plains. However, the western mountains—the Andes—are much higher than those of North America; South America's plains are less extensive, and its eastern highlands more widespread. Moreover, the pattern of climates is quite different from that of North America because most of South America lies in the tropics.

South America's long coastline has relatively few prominent peninsulas or indentations. The Pacific coast in particular has very few natural harbors, except in the extreme south. On the Atlantic coast there are more bays and inlets, but these are often far from large cities, or are isolated from the interior by coastal mountains. Islands lie primarily near the extreme northern and southern ends of the continent; notable are Trinidad, the Falkland and Galápagos groups, and the many islands of the southern Chile-Tierra del Fuego region.

The Andes, a snowcapped range of mountains more than 4,000 miles (6,400 km) in length, constitute South America's most prominent physical feature. Stretching along or near the west coast from the Caribbean Sea to Tierra del Fuego, the Andes form one of the world's longest continuous mountain barriers. The Andes are geologically young, with jagged peaks and steep, rocky slopes. There are many volcanoes, both active and dormant, and the entire region is an active earthquake zone. More than 20 peaks exceed 20,000 feet (6,100 m) above sea level; Argentina's Aconcagua, which reaches 22,834 feet (6,960 m), is the world's highest peak outside Asia.

For most of their length, the Andes consist of two and sometimes three cordilleras, or chains; between them are deep valleys and high intermontane basins and plateaus. In these lofty mountain-rimmed areas, where the altitude brings relief from the equatorial climate of the lowlands, live most of the people of Colombia, Ecuador, Peru, and Bolivia. The ruggedness of the terrain and the lack of easy passes through the Andes have long isolated various parts of each country and prevented the building of adequate transportation systems.

Occupying a large part of eastern South America is the Brazilian Highlands, a rolling, hilly plateau lying generally 1,000 to 3,000 feet (300 to 900 m) above sea level. Elevations are somewhat higher near the Atlantic coast and in the several ranges of rounded mountains that cross the plateau. Few peaks exceed 9,000 feet (2,740 m) in elevation. Scattered across the Brazilian Highlands are tablelands of lava and other hard, erosion-resistant rock, which often end abruptly at high, steep escarpments, or cliffs. One such escarpment, the Serra do Mar, parallels portions of Brazil's coast, making transportation to the interior difficult. Many rivers draining the highlands drop over escarpments in rapids or waterfalls.

Another elevated region, the Guiana Highlands, lies in north-central South America. Resembling the Brazilian Highlands, it is a rolling plateau crossed by low mountain ranges. A few peaks in the west reach 8,000 or 9,000 feet (2,440 or 2,740 m); those in the east barely exceed 4,000 feet (1,220 m).

The lowlands and plains of South America occupy several broad regions and numerous smaller areas. Most extensive is the vast, nearly flat Amazon Basin. Its densely forested, river-laced expanse reaches 2,000 miles (3,200 km) eastward from the base of the Andes to the mouth of the Amazon River. The basin is widest in the west and narrows considerably in the east, where it is wedged between the Guiana and Brazilian highlands.

Other large lowland and plains regions adjoin the Amazon Basin. In the northwest are the Llanos, or grassy plains, of the Orinoco River basin; they extend to the shores of the Caribbean Sea. South of the Amazon Basin, across a low plateau, begins the grass- and tree-covered Gran Chaco. This sparsely populated and often desolate region merges southward with the Argentine Pampas, a flat and highly fertile plains region. The narrow southern end of the continent, east of the Andes, is called Patagonia. It is an arid and wind-swept plateau crossed by deep valleys.

All the major rivers of South America flow to the Atlantic Ocean or the Caribbean Sea. On the western slopes of the Andes, the streams flowing to the Pacific are short and carry little water. Nearly one-third of the continent is drained by the huge Amazon River system. From headwaters high in the Andes, the Amazon flows across forest-covered lowlands to its mouth at the Equator. Adding to its huge flow, the largest in the world, are hundreds of tributaries, some of which—such as the Madeira and Tapajós—are themselves major rivers.

The Orinoco River and its tributaries drain the land between the Andes and the Guiana Highlands. Far to the south are the Paraná, Paraguay, and Uruguay rivers, whose combined waters flow into the great estuary known as the Río de la Plata.

Rapids and waterfalls are common on South American rivers; they often prevent navigation. In the highlands of Venezuela is Angel Falls, the world's highest waterfall, formed where a river drops more than 3,000 feet (900 m) from an escarpment. Impressive Iguassu Falls, on the Brazil-Argentina border, is higher and much wider than Niagara Falls.

South America is almost as poor in lakes as it is rich in rivers. Aside from reservoirs, nearly all the lakes are in or near the Andes. Lake Titicaca, in an Andean basin 12,500 feet (3,810 m) above sea level, is the largest freshwater lake. Venezuela's Lake Maracaibo has a larger surface area, but its northern half is brackish. Glacial lakes dot the southern Chile-Argentina border area.

About two-thirds of South America lies in the tropics and, except for the Andes and higher parts of the Brazilian Highlands, has warm to hot weather all year. The narrow, tapering southern part of the continent extends into the middle latitudes and has subtropical and temperate conditions. Here, definite warm and cool seasons create climatic variety lacking in the tropics. Nowhere in South America is the range of temperatures as great as that of North America. Highs of more than 100° F. (38° C.) are relatively rare, as are lows approaching 0° F. (–18° C.).

Tropical South America has an almost unvarying daily temperature range between about 72° and 90° F. (22° and 32° C.). The lowlands of the north—including the Amazon Basin; the coasts of Guyana, Suriname, and French Guiana; and western Colombia—have a tropical rainy climate. Extreme humidity, constant heat, and almost daily rainfall are typical.

A tropical wet-and-dry climate prevails on both sides of the Amazon Basin, in the Orinoco lowlands and the Brazilian Highlands, and south into the Gran Chaco. A pronounced dry spell, becoming longer as distance from the Equator increases, occurs when the sun is on the opposite side of the Equator. Temperatures are warm to hot virtually the whole year, except for occasional cool periods in areas well away from the Equator. Northeastern Brazil suffers from very irregular rains and has frequent serious droughts. When rains do arrive, disastrous flooding often results.

Subtropical and temperate climates reach from southern Brazil into Uruguay and over most of Argentina. Average summer temperatures in these areas vary from roughly 70° to 80° F. (21° to 27° C.) except in southern Argentina (Patagonia), which is substantially cooler. Temperatures in winter average about 20 to 30 Fahrenheit degrees (11 to 17 Celsius degrees) cooler. Precipitation is generally 20 to 50 inches (510 to 1,270 mm) yearly. Desertlike conditions occur from western Argentina southeastward over Patagonia to the Atlantic coast. Rainfall varies from scarcely 5 inches (130 mm) near the Andes to about 20 inches (510 mm) in southern Patagonia. Tierra del Fuego's remote islands are cool, rainy, and windy.

The Andes exert a profound influence on both temperature and rainfall. As elevation increases in the mountains, temperatures become progressively lower. At high elevations, constant cold prevails, with snowfields and glaciers on some peaks. The mountains are also a barrier to moist winds, causing windward slopes to be quite rainy, while the leeward sides may be dry.

The Pacific coast from central Peru through northern Chile is one of the driest regions on earth. A cold current offshore and the barrier effect of the Andes combine to prevent rain. Not even the slightest rainfall has ever been recorded in some parts of the Atacama Desert in northern Chile. Southward along the Pacific coast, the climate gradually becomes more humid. Central Chile has a climate similar to that of southern California. Southernmost Chile resembles North America's Pacific Northwest and the southeast Alaskan coast. Here, the weather is continually cool, windy, and rainy, with many areas receiving 100 inches (2,540 mm) or more yearly.