INSTITUTO ARGENTINO DE NIVOLOGIA, GLACIOLOGIA Y CIENCIAS AMBIENTALES
Unidad Ejecutora - UE
congresos y reuniones científicas
Rock Glaciers of the Central Andes
Congreso; RESOURCES AND RISKS OF REGIONS WITH PERMAFROST; 2014
The Central Andes of Argentina and Chile are one of the areas with the high-est density of rock glaciers in the world (Trombotto et al., 1999). Negative topo-95graphy or concave bases and debris, built by rocks which are susceptible to cryo-fragmentation, as eruptive rocks for example, enable considerable detritic accumu-lations to be built. The latter freeze and enrich the ice through different processes. Permafrost-ice or periglacial ice as found in protalus and protalus ramparts at the mountain permafrost level and particularly in cryogenic glacigenic embryonic rockglaciers, may be associated to pre-existent glaciers and also to nivo-detritic avalanche phenomena, which incorporate snow to their open fabric or to the slow processes of infiltration of precipitation into the cryosediments, which either freeze or turn into ice once they reach the depth of the 0 ºC isotherm. The first time ever that cryoforms rich in ice are protected by law ? a law approved in Argentina ? triggered the elaboration of a national inventory of Andean rock glaciers focusing on a classification of cryoforms. This classification is based on the genesis of cryo-forms and on the type of structure or shape observed. Different methods were ap-plied for this purpose: direct methods during fieldwork and indirect methods such as the interpretation of images and aerial photographs. Even though there are cases of rock glaciers directly linked to glaciers and covered glaciers (with debris or se-diment layers on their outer surface) which are common examples in the Andes, it has to be pointed out, that cryogenic and composed rockglaciers, where the men-tioned cryoforms interfere with cryogenic rock glaciers (without glacigenic inter-vention) are also typical and frequent cases of the Andean environment. The feed-ing zones may derive from cryogenically active moraines in case of the glacigenic rock glaciers, or from different ?roots? where various nivo-detritic avalanche channels are identified, which contribute to the growth of ice (Trombotto and Bor-zotta, 2009). Other than in the cases of Arctic permafrost, the glacier fronts of the Andean rock glaciers have an active layer with a thickness of more than 4 m. The thickness of permafrost figured by geophysical methods exceeds 50 m in numerous cases.