Dynamic changes of a large ice-debris complex in the Central Andes of Argentina

Active rock glaciers and ice-debris complexes constitute important indicators of permafrost in periglacial environments of high mountain regions. Within the permafrost body and the seasonally frozen active layer, these cryogenic landforms potentially store significant amounts of water. Especially in dry mountain belts, such as the central Andes of Argentina, rock glaciers and ice-debris complexes attain several kilometres in length, even outranging glaciers in size and number. This intriguing observation fostered discussions on their importance as water reservoirs in this semiarid part of the Andes, yet studies addressing this issue in the region remain sparse.  

Here we present data on the internal composition, surface velocities and volumetric changes of the Morenas Coloradas ice-debris complex (>2 km²), located close to the City of Mendoza in the central Argentinian Andes that we derive from Electrical resistivity tomography (ERT) measurements and repeated aerial surveys collected in the years of 2016 and 2019. In addition, we compare our newly gathered data with earlier studies as well as aerial imagery from the late 1960ies.

Our geophysical data indicate massive ice in the central upper part of the Morenas Coloradas complex, which is supported by field observations and remote sensing data, showing a zone of active thermokarst development with massive ice capped by a 2-4 m thick layer of debris. In the lower parts of the ice-debris complex, thermokarst phenomena are absent. Still, our geophysical data point to frozen subsurface conditions, but lower resistivities indicate ice-debris mixtures instead of massive ice here.

Between 2017 and 2019, surface velocities of the Morenas Coloradas ice-debris complex largely varied between 0.5 and 4 m yr^-1. The highest displacement rates are found in the central upper part of the landform, where two tributaries join the main stem of the complex, as well as in the lower part of the extensive tongue that reaches down to ~3600 m asl. While the landform shows active deformation on the full width of ~500 m in the upper and central parts, active displacement is funnelled into a small band in the lower part approaching the frontal position. Comparing our results to aerial imagery from the late 1960ies, we find surprisingly little variation in the displacement pattern and magnitude, despite the considerable dynamics during more than five decades of warming climate and changes in precipitation patterns. In terms of volumetric changes, however, we find that the Morenas Coloradas ice-debris complex has lost roughly 110,000 m³ between 2017 and 2019 in the lower 2/3 of the landform that is covered by our data. Interestingly, volumetric loss is focused on the central upper part (~80 % of total loss) where large thermokarst ponds attest the rapid degradation. The lateral parts and lower reaches, in contrast, show little absolute volumetric change over observation period from 2017 to 2019.