Andes - geography.

Andes - geography. I INTRODUCTION Andes, the principal mountains of South America and one of the greatest mountain systems of the world. The Andes include some of the world's highest peaks. More than 50 of them soar higher than 6,100 m (20,000 ft) above sea level. Only the Himalayas of south central Asia are higher. The lofty plateaus and high mountain valleys of the Andes contain some of the highest permanent human settlements in the world. The Andes are the longest system of high mountain ranges on earth. They extend for more than 8000 km (5000 mi) in a narrow belt along the western edge of the South American continent, from the coast of the Caribbean Sea in the north to the island of Tierra del Fuego in the extreme south. Along almost its entire length, the Andes rise abruptly from the Pacific coast. The mountains reach into seven countries: Venezuela, Colombia, Ecuador, Peru, Bolivia, Chile, and Argentina. The Andes formed during the Cretaceous period (about 138 million to about 65 million years ago) when the Pacific crustal plate began to slowly slide beneath the South American plate, uplifting and folding the sedimentary rocks that comprise the Andes (see Plate Tectonics). Tectonic forces generated by this collision still trigger earthquakes and volcanic eruptions. Within the range are lofty plateaus, such as the plateau of Quito (about 3,000 m/about 10,000 ft) in Ecuador and that of Lake Titicaca (4,000 m/13,000 ft) in southern Peru and Bolivia. II THE PRINCIPAL RANGES OF THE ANDES The mountain belt is generally about 300 km (about 200 mi) wide, except in Bolivia, where it expands to twice that width. From north to south the belt can be divided into three regions: a northern section in Venezuela, Colombia, and northern Ecuador; a central section in southern Ecuador, Peru, Bolivia, and the northern regions of Argentina and Chile; and a southern section in the southern regions of Argentina and Chile. The northern Andes curve in an arc from northeast to southwest. The arc consists of three main parallel ranges, known as the Cordillera Occidental (Western Cordillera), the Cordillera Central (Central Cordillera), and the Cordillera Oriental (Eastern Cordillera). The term cordillera, which is now used to describe mountain ranges in many parts of the world, comes from a Spanish word meaning rope. Early European explorers used the word to describe the roughly parallel formation of many Andean ranges. In the north the ranges fan out. The Cordillera Oriental divides into the Cordillera Mérida, which extends along the east coast of Lake Maracaibo in Venezuela, and the Sierra de Perijá, which extends to the west of Lake Maracaibo along the borders of Colombia and Venezuela. Both of these ranges extend to the Caribbean Sea. Farther south the three major ranges draw closer to one another in Colombia and narrow further in Ecuador to form two main ranges. The central Andes extend from northern Peru southeastward to southern Bolivia and then trend due south. They include the widest part of the mountain system and some of its highest peaks. The two main ranges of the central Andes, which are also known as the Cordillera Occidental and the Cordillera Oriental, enclose the Altiplano, an extensive plateau in Bolivia and southern Peru between 3,600 to 4,000 m (12,000 to 14,000 ft) above sea level. Farther south is another high plateau, called the Puna de Atacama, located mostly in Argentina along the northwest border with Chile and Bolivia. The southern Andes narrow to form a single range, which curves to the east at its southern end. The highest mountain in the western hemisphere, Aconcagua (6,960 m/ 22,834 ft), is located in this section of the Andes in Argentina. South of Aconcagua the mountains diminish gradually in height. Cerro Yogan, the highest peak on Tierra del Fuego, rises to only 2,469 m (8,100 ft). III ROUTES AND PASSES The Andes present a much more formidable barrier to east-west transportation and communication in South America than do the Rocky Mountains in North America. Although the mountain belt of the Andes is narrower than that of the Rockies, the peaks are much higher. Except in the southern section, most Andean passes are more than 3,000 m (10,000 ft) above sea level and are blocked by snow for several months of each year. Even in the south the rugged terrain prevents the use of many lower passes. The pass from Arequipa to Puno, in Peru, is 4,470 m (14,660 ft) high; the pass from Lima to Tarma and Cerro de Pasco, also in Peru, is 4,800 m (15,760 ft) high; and the Uspallata Pass, between Mendoza, Argentina, and Santiago, Chile, reaches a maximum height of about 3,800 m (about 12,500 ft). The Uspallata Pass is a major transportation route between Chile and Argentina. A highway follows the pass, and a railroad tunnel runs underneath it. Railroads have been built through several other passes. They include two in Peru--the Central Railroad, which links Lima and La Oroya, and the railroad connecting Mollendo with Puno. IV RIVERS AND LAKES The rivers flowing toward the Pacific are short and small in volume because the rainfall on the western slopes of the mountains is limited. The streams to the east are long and supplied with an abundance of water from the trade winds, which deposit precipitation as they approach the mountains. These mountain streams are the source of the major headstreams of the three great river systems of South America: the Amazon, which flows through Peru and Brazil; the Orinoco of Colombia and Venezuela; and the Parana-Paraguay-Uruguay river system, which empties into the Rio de la Plata, a large marine estuary along the Atlantic coast between Uruguay and Argentina. There are many large mountain lakes, particularly in southern Chile and Argentina. Lake Titicaca, on the Altiplano along the border between Peru and Bolivia, is the highest large navigable lake in the world. It lies in a watershed that has no outlet to the ocean. The lake covers an area of about 8,300 sq km (about 3,200 sq mi). Its surface lies 3,800 m (12,500 ft) above sea level. V CLIMATE The climate in the Andes varies greatly. In general, the northern section is rainy and warm; the central section is dry, with great extremes of temperature; and the southern section is rainy and cool. Altitude and other factors modify climatic conditions, especially near the equator where the range of temperatures varies greatly at different altitudes. The mountains also have a major effect on the climates of the surrounding areas, as they prevent much of the moisture carried by trade winds off the Atlantic from passing to the western side of the mountains, where rainfall is very limited between the equator and southern Chile. The permanent snow line in the northern and central Andes varies in height from about 4,600 to 5,300 m (about 15,000 to 17,500 ft), and all the highest peaks are snowcapped throughout the year. In the southern Andes the snow line is much lower and is only about 900 m (about 3,000 ft) in southern Chile. There are extensive glaciers in the southern Andes. VI PLANT AND ANIMAL LIFE In the northern Andes and in parts of the central Andes, evergreen tropical rain forest covers the lower slopes. From Venezuela to central Bolivia a dense growth of smaller trees lies above the zone of rain forest. Among the smaller trees is found the wild cinchona, a source of quinine, a drug used to treat malaria. In the southern Andes, broadleaf and coniferous trees cover the lower slopes. Coniferous forests are found above 2,000 m (6,500 ft), and the timberline is generally about 3,000 m (about 10,000 ft) above sea level. Above the timberline are treeless highland meadows, but the high plateaus of the central Andes support only a sparse covering of grasses and stunted shrubs. The most important native domestic animal of the Andes is the llama, a member of the same family as the camel. The llama, found predominantly in Peru and Bolivia, can live at high altitudes. It is used as a beast of burden and yields wool, milk, and meat. The alpaca, an animal related to the llama, is raised for its wool. Wild animals include the vicuña, which is another member of the camel family, and the chinchilla, which is a member of the rodent family. Both the vicuna and the chinchilla are prized for their pelts. The birds of the Andes include the condor, the largest of all birds of prey. VII ECONOMIC ACTIVITIES AND HUMAN SETTLEMENT The Andes are rich in mineral deposits, including gold, silver, copper, platinum, mercury, lead, iron ore, petroleum, and sulfur. Indigenous people mined gold and silver prior to the Spanish conquest of the area in the 16th century. Today, copper is mined in Chile and Peru, and antimony and tin are mined in Bolivia. Many of the mines are more than 4,600 m (15,000 ft) above sea level. Some farming is carried on at high altitudes, especially in the Altiplano, where grain and potatoes are grown at about 3,700 to 4,000 m (about 12,000 to 13,000 ft) above sea level. Sheep, alpacas, and llamas are pastured on the high mountain slopes. Tourism is also a major source of revenue in some areas, such as in Peru where tourists visit the ancient cities of Machu Picchu and Cuzco. These sites were constructed by the Incas, a preColombian people who built an extensive civilization extending from central Chile to northern Ecuador. Settlements in the high Andes include La Paz, which is the seat of government of Bolivia, and Quito, which is the capital of Ecuador. La Paz, which is about 3,600 m (about 11,900 ft) above sea level, is the highest large city in the world. Cuzco, Peru, was the capital of the ancient empire of the Incas and is the capital of one of Peru's 25 governmental departments. For centuries parts of the Andes have been densely populated by indigenous farmers and herdsmen. Today many indigenous people live and work in much the same way as their ancestors did under the rule of the Incas and, later, of Spanish colonists. Crops are often planted on hillside terraces, constructed to take advantage of scarce agricultural land located on steep terrain. Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.