Distribution of glaciers in South America

A number of glaciers exist in the Andes, extending from the Equator to 55°S on the western side of South America. They are in the forms of small hanging or cirque glaciers, valley glaciers, ice caps and vast ice fields. In terms of glacier area, about 65% of the total is made up by two separate icefields in Patagonia (45°-53°S), with the rest located mostly at high altitudes in the Andes from 10°N to 45°S (Williams & Ferrigno, 1998), and in

Tierra del Fuego and other small islands in southern Patagonia (Holmlund & Fuenzalida, 1995; Casassa et al., 2002b).

The distribution of glaciers and the total glacierized surface area in each region of South America are summarized in Table 46.1. The methods and the standards used to compile glacier areas vary between the regions (or authors). Some include only inventoried glaciers, whereas others include estimates of unin-ventoried glaciers. If we simply take a sum of the areas, the total glacierized area in South America yields 26,100 km2, compared

Table 46.1 Glacier areas in South America

Country

Region

Total glacier areaf

(km2)

Venezuela

Sierra Nevada de Merida

*3

Columbia

Sierra Nevada de Santa Marta and others

* 111

Ecuador

Cordilleras Oriental and Occidental

*120

Peru

Cordillera Blanca and others mountains

**2042

Bolivia

Cordilleras Oriental and other mountains

*566

Chile

Andes other than Patagonia Icefields

**2015

Argentina

Andes other than Patagonia Icefields

*1385

Chile

Northern Patagonia Icefield

***4200

Chile-Argentina

Southern Patagonia Icefield

*** 13,000

Chile-Argentina

Tierra del Fuego

*2700

tSources: * IAHS(ICSI)-UNEP-UNESC (1989); **Casassa et al. (1998); ***Aniya (1999).

tSources: * IAHS(ICSI)-UNEP-UNESC (1989); **Casassa et al. (1998); ***Aniya (1999).

with an area of 25,900km2 reported by IAHS(ICSI)-UNEP-UNESCO (1989).

The north-south distribution of the present equilibrium line altitude (ELA) along the Andes has been roughly estimated based on aerial photographs by Nogami (1972). The ELA rises gradually from the Equator to around 25°S, which corresponds to the Atacama Desert in the northern Chile, and lowers sharply from 30°S to 42°S in northern Patagonia. This abrupt descent in the ELA is attributed to the prevailing westerlies south of 35°S, which carry moisture from the Pacific Ocean (Ohmura et al., 1992). More detailed estimates have been made in the central Andes using photographs, topographic maps and Landsat imageries. In the Cordillera Blanca (7°-10°S), the mean ELA is located around 5000 m a.s.l., whereas it is significantly lower at about 4400 m on the eastern side (Amazon Basin) of the Cordillera Oriental (Rodbell, 1992). This trend is interpreted to be due to the effect of precipitation distribution resulting from vapour advection from the Amazon basin in the east (Casassa et al., 1998). The major feature of the present ELA in the tropical Andes is the general rise from northeast to southwest: the ELA rises westward to 5100 m in central Peru and rises southwestward to the extremely high altitudes >5800 m in the western cordillera along the Bolivia-Chile border (Klein et al., 1999).

In South America, tropical glaciers experience strong solar radiation and very dry conditions. The climate in the Cordillera Blanca is characterized by relatively large daily and small seasonal temperature variations as well as by a distinct succession between dry and wet seasons (Kaser et al., 1990). Although only a few studies have been performed on mass balance and variations of glaciers in the tropical and central Andes, it is known that recently most glaciers have retreated. For example, drastic shrinkages of small glaciers in the Cordillera Real (16°S) in Bolivia have been observed during the past two decades, and a probable extinction of these glaciers in the near future could seriously affect the hydrological regime and the water resources of the high-elevation basin (Ramirez et al., 2001). In northern and central-south Chile (18°-41°S), the 13 glaciers studied have all receded during the past 40 or 50yr (Rivera et al., 2002).

In contrast to glaciers in the high Andes, glaciers in Patagonia (south of 40°S) are located at lower altitudes and typified by tem perate, maritime glaciers with high accumulation and ablation throughout the year. In Patagonia, the ELAs of most glaciers range from about 900m to 1300m (Aniya, 1988; Aniya et al., 1996). In the following sections, we concentrate only on the characteristics and behaviour of Patagonian glaciers.

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