Geographical Divisions

The Andes are a geologically young and complex series of folded and faulted mountains. There are major volcanic areas, especially in southern Colombia and Ecuador, from southern Peru to northern Argentina, and in the south-central part of Chile. The entire Andean region is an active earthquake zone.

The Northern Andes begin in Venezuela and Colombia, where the mountain ranges rise almost directly from the Caribbean sea. In Colombia, deep river valleys divide the Andes into the three distinct cordilleras. Farther south, in Ecuador, the mountains consist of two chains, separated by a deep rift valley. Dotting the chains are numerous volcanoes, including Chimborazo and Cotopaxi. The Andes reach their narrowest point in Ecuador, where the crests of the ranges are as little as 20 miles (32 km) apart.

The Central Andes begin in northern Peru and broaden into high plateaus, on which are mountain ranges and volcanic peaks. As in the northern section, there are two or three major ranges depending on location.

In southern Peru and western Bolivia, the ranges enclose an area of high intermontane basins called the Altiplano (high plain). Most of this area lies at elevations of more than 12,000 feet (3,600 m). To the southeast, along the eastern margin of the Andes, is a high, dry region called the Puna. The Andes are at their widest in Bolivia, where the eastern and western ranges are as much as 400 miles (640 km) apart.

As the Andes narrow in northern Argentina and Chile, they form a single principal range. Here are the highest mountains of the Americas, including many volcanoes.

The Southern Andes stretch from central Chile to the tip of the continent at Cape Horn. In general, they are lower than the ranges to the north, although there are high, isolated volcanic peaks. The mountains have been heavily glaciated, especially in the extreme south, where large glaciers still exist. For much of their course the Southern Andes plunge directly into the sea, creating a rugged, indented shoreline, with many offshore islands.