Microscopical characterization of thermokarst ice from an area of Andean permafrost, Central Andes of Mendoza, Argentina

ARENA, LUCÍA; TROMBOTTO, DARIO; CARANTI, GIORGIO

Potsdam, Alemania

Conferencia; 2nd European Conference On Permafrost; 2005

European Permafrost Association

The analyses focus on ice samples extracted from thermokarst in an area without uncovered ice but with ice covered by sediments, and thus constituting a completely new and recent periglacial environment. That way, the permafrost level extends to heights over 4200-4300 m, hidden under a thick layer of sediments. The study area is located in the Cordon del Plata in the Andean Cordillera of Mendoza, Argentina. The samples are taken from two profiles and different walls of the thermokarst that were analysed between 1999 and 2002. It was proven that through the techniques of plastic replica and thin layers studied under crossed polarizers, it is possible to establish microscopical differences between sedimentary ice and glacigenic ice under stress. In the present work microcrystallographic studies of samples extracted from two almost perpendicular thermokarst walls are compared. In the first case, an E-SE wall sampled in 1999, the samples were exposed to a major pressure in direction of the glacial flow than that of the second case, a N-NW wall examined in 2002, where the glacial flow caused mainly shear stress. These facts influence the structure and the internal characteristics of the ice. The results of this work allow to distinguish between glacigenic ice, with bubbles that are deformed in the direction of the main flow of the glacier, and the sedimentary ice with completely spherical bubbles. In the samples of the sedimentary ice, taken in 2002, a very low density of bubbles is observed and the average size of the crystals is considerably bigger than in 1999. This is interpreted as an increase of the mean temperature of the thermokarst. The reactivation of old thermokarst would also indicate a degradation of the Andean permafrost.