ABSTRACT

The Andes run along the entire western side of South America (Figure 6.1). For most of their length they are divided into the Eastern and Western Andes (Cordillera Oriental and Cordillera Real, or local variations), with an Inter-Andean Depression between. In Colombia they divide into three ranges. They consist of folded and faulted Palaeozoic and Mesozoic rocks, with Cretaceous granite intrusions and volcanics of Mesozoic and Cenozoic age. Tectonic basins such as the Lake Titicaca Basin lie between the East and West Cordillera They are grabens formed by normal faulting, and are filled with thick sediment. This depression is flanked on both sides by volcanoes-the ‘Avenue of Volcanoes’ of von Humboldt. The eastern slope of the northern Andes drops abruptly to the Amazon lowlands, and several great tributaries of the Amazon have cut through the Andean front.