Glacial decline next to stable permafrost in the Dry Andes? Vertical glacier surface changes and rock glacier kinematics based on Pléiades imagery (Rodeo basin, 2019–2025)

Abstract

The presence and volume of high-mountain cryospheric features are drastically affected by rising air temperatures – on global scale. In the Dry Andes, precipitation is extremely scarce, shifting the hydrological significance towards the solid water storages, glaciers and ground ice. While glaciers decrease in surface area and volume, periglacially stored waters, e.g., in rock glaciers, react more retarded to atmospheric forcing, potentially buffering future water availability. Despite rising air temperatures, recent studies suggest stable permafrost conditions in the Dry Andes based on borehole investigation and rock glacier kinematics for the last decade. This apparent stability may partly reflect the extreme aridity conditions, limit snow insulation and liquid-water input, thereby damping inter-annual variability in ground thermal conditions and associated changes in rock glacier creep. We investigate vertical surface changes of 19 glaciers, three debris-covered glaciers and 59 rock glaciers in the Rodeo basin (Dry Andes, Argentina) for the time period 2019–2025. Further, we calculate rock glacier velocities for 47 of the 59 rock glaciers for which we have data for all time periods. Photogrammetric principles are followed using (tri)stereo, panchromatic Pléiades imagery to generate projected optical imagery and DEMs in Ames Stereo Pipeline. Resulting DEMs are co-registered prior to DEM differencing for vertical surface change calculation. To derive rock glacier velocities, a feature tracking approach is applied to panchromatic Pléiades orthoimagery. We detect glacier surface lowering of up to -8.99 m (total change, 2019–2025) and dominantly annual surface lowering for all glaciers investigated. Vertical surface lowering on debris-covered glaciers falls well below the magnitude of glaciers, but is higher than for rock glaciers – the latter not exceeding a decimetre. Average rock glacier velocities fall between 0.28 and 0.82 m yr−1 (Levels of Detection, LoDs: ±0.16, ±0.61). The presence of highest magnitude of horizontal velocities is different between rock glaciers, with highest horizontal velocities partially reached in the upper or lower part of the rock glacier surface. Across the 47 rock glaciers investigated, no regional trend of increasing velocities is found. In conclusion, the declining glacial domain contrasts with unchanged rock glacier velocities which elucidate stable permafrost conditions. We infer a delayed reaction of the periglacial domain to the rising temperatures that lead to the surface lowering of glaciers and highlight the need for ongoing, long(er)-time surface change monitoring in this crucial, dynamic point in time.