Volumetric and kinematic assessment of the current state of the Morenas Coloradas ice-debris complex, Cordón del Plata, Argentina

JAN HENRICK BLÖTHE; CHRISTIAN HALLA; ESTEFANÍA BOTTEGAL; LOTHAR SCHROTT; DARIO TROMBOTTO LIAUDAT

Puerto Madryn

Congreso; XXI Congreso Geológico Argentino; 2022

Active rockglaciers and ice-debris complexes are indicators of permafrost in periglacialenvironments of high mountain environments. Within the permafrost body and theseasonally frozen active layer, these cryogenic landforms potentially storesignificant amounts of water. Especially in semiarid mountain belts, such asthe Central Andes of Argentina, rock glaciers and ice-debris complexes attainseveral kilometres in length, frequently covering surface areas of >1 km2.Here, these cryogenic landforms even outrange ice glaciers in cumulative areaand absolute number, indicating they might constitute an important waterreservoir in this semiarid part of the Andes (Azócar and Brenning 2010). Currently,there are only few specimen in the Central Andes that were monitored on decadaltime scales. The Morenas Coloradas ice-debris complex (>2 km2), located inthe Cordón del Plata ranges, close to the City of Mendoza, has been the subjectof many studies that investigated its internal structure, icevolumes, surfacevelocities and volumetric change (Barsch and King 1989, Trombotto and Borzotta2009, Trombotto-Liaudat and Bottegal 2019, Blöthe et al. 2021). Herewe present data on its internal composition, surface velocities and volumetricchanges that we derive from Electrical resistivity tomography (ERT)measurements and repeated aerial surveys collected in the years of 2016 and2019. In addition, we compare our newly gathered data with earlier studies aswell as aerial imagery from the late 1960ies. Our geophysical surveys indicatemassive ice to dominate in the central upper part of the Morenas Coloradascomplex, which is supported by field evidence and remote sensing data, showinga zone of active thermokarst development with massive ice capped by a 2-4 mthick layer of debris. In the lower parts of the complex, approaching the toeposition, no thermokarst development is visible. Still, our ERT data point tofrozen subsurface conditions, but lower resistivities indicate ice-debrismixtures instead of massive ice here. Between 2017 and 2019, surface velocitiesof the Morenas Coloradas ice-debris complex mainly varied between 0.5 and 4 myr-1 (Fig. 1). The fastest displacement is found in the central upper part ofthe landform, where two tributaries join the main stem of the complex, as wellas in the lower part of the extensive tongue that reaches down to ~3600 m asl.While surface displacement can be detected on the full width of the landform inthe upper and central part, it is funnelled into a small band of active deformationin the lower part approaching the frontal position. Comparing our results toaerial imagery from the late 1960ies, we find surprisingly little variation inthe displacement pattern and magnitude, despite the considerable dynamicsduring more than five decades of warming climate and changes in precipitationpatterns. Looking into the volumetric changes, however, we find that theMorenas Coloradas ice-debris complex (our data covers the lower 2/3 of thelandform) has lost roughly 110,000 m3 between 2017 and 2019. Interestingly,volumetric loss is focused on the central upper part (~80 % of total loss)where large thermokrast ponds attest the rapid degradation. The lateral partsand lower reaches, in contrast, show little absolute volumetric change overobservation period from 2017 to 2019.