South America
South America, the fourth largest continent on Earth, encompasses an area of 6,880,706 square miles (17,821,028 square kilometers). This is almost 12 percent of the surface area of Earth. At its widest point, the continent extends about 3,200 miles (5,150 kilometers). South America is divided into 12 independent countries: Argentina, Bolivia, Brazil, Chile, Colombia, Ecuador, Guyana, Paraguay, Peru, Suriname, Uruguay, and Venezuela. French Guiana, an overseas department (territory) of France, also occupies the continent.
The continent of South America can be divided into three main regions with distinct environmental and geological qualities. These are the eastern highlands and plateaus, the large Amazon River and its basin in the central part of the continent, and the great Andes mountain range of the western coast.
The highlands and plateaus
The eastern highlands and plateaus are the oldest geological region of South America. They are believed to have bordered on the African continent at one time, before the motion of the plates that make up Earth's crust began separating the continents about 140 million years ago. The eastern highlands and plateaus can be divided into three main sections.
The Guiana Highlands are in the northeast, in south Venezuela and northeastern Brazil. They are about 1,200 miles (1,930 kilometers) long and from 200 to 600 miles (320 to 965 kilometers) wide. Their highest peak, Mount Roraima, reaches a height of 9,220 feet (2,810 meters). This is a moist region with many rivers and waterfalls. It is in this range, in
Venezuela, that the highest waterfall in the world is found. Called Angel Falls, it cascades freely for 3,212 feet (980 meters).
The great Plateau of Brazil covers more than one-half of the area of Brazil, and ranges in altitude between 1,000 and 5,000 feet (305 and 1524 meters). The highest mountain range of this highland region is called Serra da Mantiqueira, and its highest peak, Pico das Agulhas Negreas, is 9,141 feet (2,786 meters) above sea level.
The Plateau of Patagonia is in the south, in Argentina. The dominant mountain range of this highland area is Sierras de Cordoba. Its highest peak, Champaqui, reaches an altitude of 9,459 feet (2,883 meters).
The Amazon basin
The Amazon basin (the area drained by the Amazon River) is the largest river basin in the world. It covers an area of about 2,500,000 square miles (6,475,000 square kilometers), or almost 35 percent of the land area of South America. The volume of water that flows from the basin into the Atlantic is about 11 percent of all the water drained from the continents of Earth. The greatest flow occurs in July, and the lowest in November.
The Amazon basin was once an enormous bay, before the Andes Mountains were pushed up along the coast by the movement of the crust-forming plates. As the mountain range grew, it held back the ocean and eventually the bay became an inland sea. This sea was finally filled by the erosion of the higher land surrounding it, and finally a huge plain, crisscrossed by countless waterways, was created. Most of this region is still at sea level and is covered by lush jungle and extensive wetlands. This jungle region contains the largest rain forest in the world, which is home to an uncounted number of plant and animal species found nowhere else in the world.
While there are many rivers flowing through the basin, the most important and well-known of these is the Amazon River. It runs for about 3,900 miles (6,275 kilometers), from the Andes Mountains in northern Peru to the Atlantic Ocean near Belem, Brazil. When it enters the ocean, the Amazon discharges about 7,000,000 cubic feet (198,240 cubic meters) of water per second. The width of the Amazon ranges from about 1 to 8 miles (1.6 to 13 kilometers). Although the Amazon is usually only about 20 to 40 feet (6 to 12 meters) deep, there are narrow channels where it can reach a depth of 300 feet (91 meters). Almost every year, the Amazon floods, filling a flood plain up to 30 miles (48 kilometers) wide. The fresh layer of river silt deposited by the flood makes the surrounding region extremely fertile.
The Andes
The Andes Mountains constitute South America's great mountain range. They extend more than 5,000 miles (8,045 kilometers) up the western coast of the continent, passing through seven countries—Argentina, Chile, Bolivia, Peru, Ecuador, Colombia, and Venezuela. The highest peak of the Andes, called Mount Aconcagua, is on the western side of central Argentina, and is 22,835 feet (6,960 meters) high. Lake Titicaca, the world's highest large freshwater lake, is located in the Andes on the border between Peru and Bolivia at a height of 12,500 feet (3,800 meters) above sea level.
The Andes were formed by the motion of crustal plates. Millions of years ago, the South American plate (on which the continent sits) broke away from the African plate. When the western edge of the South American plate met the eastern edge of the Nazca plate under the Pacific Ocean, the Nazca plate subducted or slid under the South American plate. (Since continental plates are less dense than oceanic plates, they ride over them.) This motion caused the western edge of the South American plate to buckle, fold, and be thrust upwards, forming the Andes Mountains. As the Nazca plate continues to sink under the surface, its leading edge is melted by the extreme temperatures and pressures inside Earth. Molten rock then rises to the surface, lifting and deforming it. To this day, the Andes are still rising.
This geological instability makes earthquakes common all along the western region of the continent. The Andes are dotted with volcanoes. Some of the highest peaks in the mountain range, which rise above 20,000 feet (6,100 meters), are volcanic in origin. The Andes in Chile contain the greatest concentration of volcanoes on the continent: over 2,000 active and dormant volcanoes. The area is plagued by earthquakes.
The climate in the Andes varies greatly, depending on both altitude and latitude, from hot regions to Alpine meadow regions to glacier regions. The snowline is highest in southern Peru and northern Chili, where it seldom descends below 19,000 feet (5,800 meters). In the far south of the continent, in the region known as Tierra del Fuego, the snowline reaches as low as 2,000 feet (600 meters) above sea level.
The Andes are a rich source of mineral deposits, particularly copper, silver, tin, iron, and gold. The Andes in Colombia yield rich deposits of coal, while in Venezuela they contain petroleum. The largest deposits of emeralds in the world, outside of Russia, are found in the Colombian Andes. The Andes are also a source of tungsten, antimony, nickel, chromium, cobalt, and sulfur.
[ See also Plate tectonics ]