Andes

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.

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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.

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