Geology of The Andes - Climate and Hydrology

Climate and Hydrology

See also: Tropical Andes, Dry Andes, and Wet Andes

The climate in the Andes varies greatly depending on latitude, altitude, and proximity to the sea. Temperature, atmospheric pressure and humidity decrease in higher elevations. The southern section is rainy and cool, the central Andes are dry. The northern Andes are typically rainy and warm, with an average temperature of 18 °C (64 °F) in Colombia. The climate is known to change drastically in rather short distances. Rainforests exist just miles away from the snow covered peak Cotopaxi. The mountains have a large effect on the temperatures of nearby areas. The snow line depends on the location. It is at between 4,500 and 4,800 m (14,800–15,800 ft) in the tropical Ecuadorian, Colombian, Venezuelan, and northern Peruvian Andes, rising to 4,800–5,200 m (15,800–17,060 ft) in the drier mountains of southern Peru south to northern Chile south to about 30°S, then descending to 4,500 m (14,760 ft) on Aconcagua at 32°S, 2,000 m (6,600 ft) at 40°S, 500 m (1,640 ft) at 50°S, and only 300 m (980 ft) in Tierra del Fuego at 55°S; from 50°S, several of the larger glaciers descend to sea level.

The Andes of Chile and Argentina can be divided in two climatic and glaciological zones; the Dry Andes and the Wet Andes. Since the Dry Andes extends from the latitudes of Atacama Desert to the area of Maule River, precipitation is more sporadic and there are strong temperature oscillations. The line of equilibrium may shift drastically over short periods of time, leaving a whole glacier in the ablation area or in the accumulation area.

In the high Andes of central Chile and Mendoza Province rock glaciers are larger and more common than glaciers; this is due to the high exposure to solar radiation.

Though precipitation increases with the height, there are semiarid conditions in the nearly 7000 m towering highest mountains of the Andes. This dry steppe climate is considered to be typically of the subtropic position at 32-34° S. Therefore in the valley bottoms do not grow woods but only dwarf scrub. The largest glaciers, as e.g. the Plomo glacier and the Horcones glaciers do not even reach 10 km in length and have an only insignificant ice thickness. At glacial times however, c. 20 000 years ago, the glaciers were over ten times longer. On the East-side of this section of the Mendozina Andes they flowed down to 2060 m and on the West-side to c. 1220 m asl. The massifs of Cerro Aconcagua (6962 m), Cerro Tupungato (6550 m) and Nevado Juncal (6110 m) are situated deca-kilometres away from each other and were connected by a joint ice stream network. Its dendritic glacier arms, i.e. components of valley glaciers, were up to 112.5 km long, over 1020, i.e. 1250 m thick and overspanned a vertical distance of 5150 altitude metres. The climatic glacier snowline (ELA) was lowered from currently 4600 m to 3200 m at glacial times.