The Andean Glacier and Water Atlas

The Andes are the longest continental mountain range in the world, extending for more than 7,000 km from Venezuela in the north to Argentina in the south. Geographically they can be divided into three regions; the Northern Andes which includes the Venezuelan, Colombian and Ecuadorian mountains, the Central Andes which encompasses the Peruvian and Bolivian mountains and the Southern Andes which consists of the Chilean and Argentinean mountains. Together the Northern and Central Andes form the Tropical Andes. The Southern Andes is often referred to as the extratropical Andes. Peaks, plateaus and valleys

that started approximately 140 million years ago (Isacks, 1988). This collision caused the formation of a series of parallel mountain chains or cordilleras, interspersed with high peaks, plateaus and valleys. The Andes are the second highest mountain range after the Himalayas and are a defining feature of the South American continent. They have an average altitude of 4,000 m, with many peaks higher than 6,000 m above sea level (Arana, 2016). The highest mountain, Mount Aconcagua in Argentina is 6,908 m. The ongoing tectonic movement in the Andes generates frequent earthquakes and volcanic activity. Extinct or active volcanos can be found across the region, including the highest volcano on earth, Ojos del Salado in Chile, which is 6,893 m (Borsdorf & Stadel, 2015). The Dry Andes stretch over most of western Argentina and central Chile and are divided into two sub-zones: the Desert Andes, which extend from the northern boundary of Chile to the Choapa Basin (~17°30 ' –32° S) and the smaller Central Andes (32–36° S) (Lliboutry 1998; Barcaza et al., 2017). Due to low precipitation, glaciers do not occur in the Desert Andes, only permanent snow patches and glacierets (Lliboutry 1998). In contrast many large glaciers are found in the wetter central Andes, which are characterised by a Mediterranean climate with wet winters (April–September) and dry summers (October–March) (Barcaza et al., 2017). The Wet Andes is the southern sub-region of the Argentine and Chilean Andes. It extends south of the Itata river, where the elevation of the mountains decreases sharply, to Cape Horn. The area includes the heavily glacierized Patagonian Andes and the sub-polar Tierra del Fuego archipelago and is characterised by increased annual rainfall with a strong west– east gradient (Garreaud, 2009; Barcaza et al., 2017).

The Andes were formed as a result of the subduction of oceanic plates under the South American continental plate; a process

A diversity of climates

Crossing seven countries, Venezuela, Colombia, Ecuador, Peru, Bolivia, Argentina and Chile, the Andes covers three large climatic zones. These are generally defined as the Tropical Andes, the Wet Andes and the Dry Andes. Within these broad zones, however, there is considerable climatic variation – also from east to west – reflected in numerous complex sub-zones that occur as a result of orography, regional and local atmospheric circulation patterns and ocean currents. The Tropical Andes extend from their northernmost point (which includes high islands in the Caribbean), southwards until the Bolivian border (Cuesta et al., 2012). The northern part of the Tropical Andes is very wet with low seasonal temperature variability. The high rainfall sustains dense cloud forests. The southern Tropical Andes are drier, with the highest rainfall occurring during the summer months and a distinct dry season from April to September (Espinoza et al., 2015).

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