THAWING AND INCREASED RUNOFF IN THE ANDEAN ROCK GLACIERS DURING THE GLOBAL WARMING OF THE PAST DECADE

The arid Cordón del Plata in the Central Andes west of Mendoza, Argentina contains peaks >6000 m asl and many rock glaciers. We report on two, the rock glaciers Morenas Coloradas and Stepanek, in a study area located between 69º 22' to 69º 25' W and 32º 56' to 32º 58' S. We established three monitoring sites on Morenas Coloradas, “Balcón I” and “Balcón I superior” at 3560 and 3590 m asl, respectively, and Balcón II at 3770 m asl. The rock glaciers showed different rates of movement at their monitoring sites, which were may be explained by climatic variability and altitude; however, the internal cryogenic structure was also destabilized due to melting and water flow. Balcón I showed sometimes signs of permafrost aggradation. Long-term studies of shallow boreholes showed, however, that the mean annual air temperature 0 °C isotherm was at higher in altitude than the active front of the rock glacier and that the permafrost of the 90’s has risen at least 40 m. At the monitoring area of “Balcón I superior”, geodesic measurements of rock glacier movement from 2013 to 2015 revealed displacements of ~2 m to the south. Thermocarst depressions express degradation of dead ice that was integrated in the rock glacier until ca 3770 m asl (Balcón II), but in contrast, the geodetic points close to Balcón II, above 3700 m asl, showed less movement indicating only 20-30 cm towards the S during the considered periods and more stability. The present study indicates that the largest cryogenic activity is located in the active layer and is due to internal movements facilitated by melt water coming from the top of the rock glacier and both sides of the upper basin of the valley. This is consistent with observed physical changes in the rock glacier. A contemporaneous stable-isotope study site, of the Stepanek rock glacier in the Cordón del Plata reveals that recharge of both surficial water and groundwater occurs from within the rock glacier. This process may be accelerated by global warming. This research allows the estimates of the quantities of different water sources flowing through the rock glacier. Future work is assessing the stability and mechanism of rock glacier degradation and potential impacts on water supply downslope.