Mapping and permafrost altitudes in a periglacial environment: The Laguna del Diamante Reserve (Central Andes, Argentina)

摘要

The Laguna del Diamante Reserve, in the Province of Mendoza (Argentina), a protected area in a volcanic caldera (around 15 km in diameter), encloses the Maipo Volcano, 5,323 m (a snow and ice-capped volcano), and the Diamante Laguna at 3,300 m a.s.l., which constitutes an important water resource for the province. A geomorphological map, made on an ASTER image from aerial photographs and corroborated by fieldwork, reflects how this area, although previously glaciated, is at present an outstanding periglacial environment with a few residual glaciers. Talus slopes, debris cones, alluvial fans, debris flow deposits, landslides and rockglaciers cover the Maipo flanks and the slopes surrounding the caldera. Periglacial landforms, occurrence of ice found during fieldwork, and rockglaciers were used to make a first approach to determine permafrost altitude. The inferior limit of quasi continuous permafrost at south exposition, detected by ice in a shelter in different years, is presently calculated at 3,870m a.s.l. approximately. In the same valley however, and considering the noses of cryoforms with creeping permafrost, cryogenic activity is observed at a height of approx. 3,750 m a.s.l. In other sites of the area, cryoforms reach down to even 3,600 m with signs of inactivity. Historic registers from 1951-1952 indicated a height below 3,850 m a.s.l. as lower permafrost limit. Palaeo - permafrost was identified at 3,400-3,500 m a.s.l. approximately on the foot of the southern slope of the Maipo Volcano. At present, the zone, still in a paraglacial state, is characterized by intense cryodynamics and it is considered adequate to be proposed as "type region".