INSTITUTO ARGENTINO DE NIVOLOGIA, GLACIOLOGIA Y CIENCIAS AMBIENTALES
Unidad Ejecutora - UE
congresos y reuniones científicas
Detection of permafrost aggradation (?) at Balcón I, Morenas Coloradas Rockglacier, Mendoza, Argentina
DARIO TROMBOTTO LIAUDAT; JAN HENRIK BLÖTHE; MARKUS KEUSCHNIG; PEPE HERNÁNDEZ; JOACHIM GÖTZ; INGO HARTMEYER; LOTHAR SCHROTT
Jornada; 3. Mitteleuropäischen Geomorphologietagung; 2008
Arbeitsgruppe Geomorphologie und Umweltsysteme, University of Salzburg
Rockglaciers are the most important geomorphological expressions of permafrost in the South American Central Andes. It is a creeping permafrost which displays its state of thermal equilibrium with the Andean mountain climate. The composed rockglacier Morenas Coloradas in Mendoza, Argentina, reveals internal variations of the permafrost table depth which are associated to regional thermal oscillations and changes of the 0°C air isotherm, possibly linked to global warming. In the late Eighties, early Nineties the permafrost table at the front of this rockglacier (3560 m a.s.l.) indicated a depth of 4.9 5 m. This depth was confirmed by thermistors placed in surface drillings carried out at this site called Balcón I and by geoelectrical prospection. Later on, a frequent monitoring initiated in 2004 and continued until present, resulted in permafrost depths of 7.5 8.5 m for the same site. The depth was determined by prolonging the temperature curves indicated by the thermistors, calculating the intersection point of linear regressions with the 0°C isotherm in the ground. The figured values have been reconfirmed during the following years until present. This phenomenon of deepening was associated to the warming process registered in the Nineties. The present analysis of these curves however allowed observing a tendency towards a gradual reduction of the thickness of the layer of unfrozen sediments in the upper part of the rockglacier since the beginning of the detected deepening of the permafrost table. Geophysical profiles carried out in 2008 correctly identified and confirmed the depth graphically and mathematically deduced with the help of temperature curves. The depth that had been detected to be in an equilibrium state between 1989 and 1992 at Balcon I was found exactly 30m higher now (Balcon I superior). The hypothesis presented in this contribution holds, that the permafrost table at the rockglacier front has reacted sensitively to a warming process in the upper sedimentary layer, possibly in the described step. However, today we find the permafrost table rising again. This process may be due to refreezing of meltwater draining down from higher parts of the rockglacier. The rockglacier at its lower altitudinal limit is tending to an aggradation of permafrost, trying to recover the equilibrium state of the cryogenic system of the past.