Introduction

The Andes dominate South America, forming a rugged backbone that stretches the entire length of the country. From the high peaks of Aconcagua (6,959m) and Ojos del Salado (the world's tallest volcano: 6,893m) the land slopes down steeply to the western coast but much more gently to the east.

The Andes, with up to three high, parallel ranges, have proved an almost impenetrable divide. There are no natural through valleys, so there are virtually no east-west communications links across the continent.

Andes

Location: 7N-53S 65-80W (S America). Length 8000km; Highest summit: Ojos del Salada: 7084m.

The Andes are a high, continuous system of volcanic mountains over 6000 m high that stretch for nearly 8000 km and form the western backbone of South America. The mountain system consists of parallel ranges (called cordilleras) of snow-capped fold mountains, often capped by volcanoes and separated by deep dry valleys.

Evidence for the collision of two crustal plates is everywhere in the landscape. Earthquakes are frequent, and most mountain volcanoes are active. The Andes forms a prominent part of the 'Pacific Ring of Fire' that marks the edges of the Pacific basin.

The Andes is widest in Bolivia, where it divides into two prominent cordilleras, separated by a high plateau called the Altiplano. Here is found Lake Titicaca, the world's highest large lake.

The Andes have a very important effect on the climate of the Southern Hemisphere. They block the rain-bearing winds to produce a rain shadow effect, and the lee side of the mountains is a desert. In the sub-tropics, where the winds blow from east to west, the rain shadow is on the west, creating the Atacama Desert of Chile,. Farther south the winds blow from west to east and the rain shadow effect is felt on the eastern side, as the Patagonian Desert of Argentina.

This mountainous terrain has been home to many native American civilisations, of which the most famous is probably the Inca civilisation. Life in the intermontane basins and mountain slopes is harsh, and much of the farming is still subsistence. This is the region where the potato originates and hundreds of varieties of potato are still cultivated by traditional methods.

Since the time of the European invaders, there has been much more exploitation of the mountains for their enormous wealth of minerals, not just gold but also copper and tin, lead and zinc.

Aconcagua

The highest summit in the Western Hemisphere (6,959 m). It riases from the central lowlands of Chile but its summit is in Argentina.

Cotopaxi
Location: 40S 78W (Ecuador); height: 5897m).

This is the tallest active volcano in the world. The center of the summit contains a snow-free crater from which steam continually pours.

Cotopaxi erupts regularly, making its upper slopes extremely dangerous for mountaineers.

Huascaran
Location: 9S 78W (Peru) Height: 6,768 m

Huascaran is the highest mountain in Peru. In 1962, earthquakes in the vicinity of Huascaran caused landslides on the the high, ice-clad slopes. A mixture of rock and ice soon plunged down the mountainside and into the deep narrow flanking valleys. The ice quickly melted and the mixture became a mudflow.

The towns below it were completely overwhelmed by the mudflow and some 3500 people were killed.

Mount Pelee
Location: 14N 62W (Martinique, West Indies). Height: 1,397 m.

Mount Pelee is an active volcano that erupted spectacularly on May 8, 1902. Part of the cone gave way allowing a glowing avalanche of ash and gas (called a glowing avalanche) to race down the flanks of the mountain to the coastal town of St Pierre. All but one of the 30,000 inhabitants were killed by the hot gas, the survivor being a prisoner in a deep dungeon. The hot gases and ash swept on over the sea, capsizing boats in the harbour and killing even more people.