Geology and Geography
A geologically young system, the Andes were originally uplifted in the Cretaceous and Tertiary periods. They are still rising; volcanoes and earthquakes are common. The folded ranges are discontinuous—merging and bifurcating within the system—but as a whole they form one of the world's most important mountain masses. They are loftier than any other mountains except the Himalayas, with many snowcapped peaks more than 22,000 ft (6,700 m) high. Andean waters reach the Orinoco, the Amazon, and the Río de la Plata.
Far south in Tierra del Fuego, the mountains run east and west, then turn north between Argentina and Chile. The westernmost of the mountains run into the sea, lining the coast of S Chile with islands. In the Patagonian Andes are high, glacier-fed lakes in both Argentina and Chile.
The highest range of the Andes is on the central and northern Argentine-Chilean border; Aconcagua (22,835 ft/6,960 m; highest mountain of the Western Hemisphere) and Tupuncato are there. Between the peaks is Uspallata Pass, the route of the former Transandine Railway, with the Christ of the Andes. Other major peaks such as Llullaillaco flank the main range, and in N Chile sub-Andean ranges enclose the high, cold Atacama Desert.
The central Andes broaden out in Bolivia and Peru in multiple ranges (c.400 mi/640 km wide) with high plateau country (the altiplano) and many high intermontane valleys, where the great civilization of the Inca had its home. High in the mountains on the Peru-Bolivia border is Lake Titicaca. In Bolivia are the notable volcanoes, Illimani and Illampú, and in S Peru is El Misti. The western or coastal range in Peru has lofty peaks (notably Huascarán) and is crossed by the highest railroad of the Andes (from La Oroya to Lima).
The ranges approach each other again in Ecuador, where the N Andes begin. Between two volcanic cordilleras (including the cloud-capped Chimborazo and Cotopaxi) are rich intermontane basins. In Colombia the Andes divide again, the western range running between the coast and the Cauca River, the central between the Cauca and the Magdalena rivers, and the eastern running north parallel to the Magdalena River, then stretching out on the coast into Venezuela. The Andes continue in some of the islands of the West Indies, and in Panama N Andean spurs connect with the mountains of Central America and thus with the Sierra Madre and the Rocky Mts.