Evolution of the active layer in a rock glacier of the Central Andes, Mendoza, Argentina, since 2008 and its relation with the kinematics of the last years

DARIO TROMBOTTO LIAUDAT; BOTTEGAL, ESTEFANÍA

Geographical Research Letters

Universidad de La Rioja

Año: 2019

0211-6820

Between 2008 and 2016 the Morenas Coloradas rock glacier inthe Central Andes of Mendoza showed different thermal characteristics at threemonitoring sites in active layers, Balcón I (3560 m asl), Balcón I Superior(3590  m asl) and Balcón II (3770 m asl).These can be explained by various factors, not only external ones related tothe climatic variability and altitude, but also by thermal-hydrological factorsthat destabilized its internal cryogenic structure. At Balcón I, situated on asloping terrace of the rock glacier, a transient layer even showed definitivesigns of permafrost degradation in the recent years, transforming it in athermal talik. Long-term studies of surficial boreholes showed that the 0 °Cisotherm is higher in altitude than the active front of the rock glacier and ithas risen 40 m in altitude since the 1990s. As consequence of the thermal changesof the active layer, the rock glacier shows abrupt movements, particularly inits terminal part. Thus geodesic measurements to obtain different speeds anddirections were made. At the monitoring area of Balcón I Superior, which lieson a superimposed lobe, the geodesic measurement points revealed significantkinematic activity in the period May 2015 ? February 2016, when the largestdisplacement was approximately 2 m to the South, developing an advance of thefront over Balcón I. At Balcón II however, the points moved much less, in theorder of 0.30 m/yr. The present studies suggest that the largest cryogenicsedimentary movements are superficial, that is to say, they are located in theactive layer and the supra-permafrost and are due to internal movementsproduced by melting water coming from the top of the cryoform, and from bothsides of the upper basin of the valley. Rock glacier, Permafrost, Activelayer, Kinematics, Climatic variability