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Rock glaciers, Central Andes, Argentina, Version 1

Primary rock glaciers are fed by avalanche chutes. At the El Salto rock glacier, surveys have been undertaken in order to determine the creep rate. Between 1981 and 1986 temperatures at elevations between 3500 and 3600 m were measured in the active layer to a depth of 1 m with a multipoint temperature recorder (Grant). On the basis of these measurement Buk (1983) determined that the permafrost table was at a depth of about 3 m and the base of the permafrost at 68 m. Similar conclusions were reached by Barsch and King (1989). As an illustration of the importance of avalanches to these forms, the base camp there was destroyed by an avalanche in November 1983. The surface of the basin of Morenas Coloradas is 54 square km, of which 10.4 square km is seasonally frozen ground. The remaining 60% of the surface is typically periglacial with rock glaciers as the most important forms. In the glacigenic rock glacier, the clean glacier ice ends in detritus-covered or morainic tongues which result in glacigenic ice being incorporated within the substrate. In this way, ice persists at lower altitudes and under very arid conditions (Lliboutry, 1986; Garleff and Stingl, 1986; Schrott, 1992). Interconnected rock glaciers are generated which undergo different phases of activity not always in agreement with those expected as a resulted of their elevations. That is, they continue to show signs of activity not only at the height of the present 0 degrees C air isotherm, but at lower elevations. In the last step downwards towards the valleys these rock glaciers become inactive, and finally morphologically relict or fossil rock glaciers are found. Meteorological, hydrological and geophysical measurements as well as 5 drillings to a depth of 5 m have been carried out in Morenas Coloradas. At an elevation of 3560 m the temperature oscillates around 0 degrees C (with a maximum variation of 0.5 degrees C) at depths between 4 and 5 m. The annual precipitation (1991-93) is 630 mm and the mean annual temperature is 1.6 degrees C. Using a calculated lapse rate of 0.52 degrees C per 100 m, the 0 degrees C isotherm occurs at approximately 3860 m, which represents a considerable rise in comparison with earlier years. It is assumed that this value is strongly influenced by climate warming in the 1980s and 1990s. Temperatures measured at different depths in Morenas Coloradas at 3560 m are positively correlated with the discharge of Rio Vallecitos (correlation coefficients of 0.8-0.9; significance p=0.01). There is no correlation with snowfall data, however, because of the influence of the 'zonda', a very dry and warm wind (up to 100 km/h) which impedes the accumulation of snow. Between 1978 and 1979, the zonda was active for more than 1000 hours. Discharge from the basin is of good quality and averages 505 l/s with a range from 230 l/s (early spring) to >1000 l/s (summer). In comparison, Schrott (1994) calculated the discharge of a rock glacier in the arid region of San Juan, Argentina to be only 5-8 l/s. These data are presented on the CAPS Version 1.0 CD-ROM, June 1998.

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