Ice thickness distribution and stability of three large freshwater calving glaciers on the eastern side of the Southern Patagonian Icefield

Abstract

The Southern Patagonian Icefield shows rapid retreat and thinning with variability in magnitude and timing among individual glaciers. To better understand these heterogeneous changes, we estimated the ice thickness distribution within the middle and lower basins of Perito Moreno, Upsala, and Viedma freshwater calving glaciers during the 2017–2018 period. We employed a surface velocity inversion method that incorporates glacier motion through internal deformation and basal slip. Additionally, we applied a directional smoothing filter to estimate surface slope and a calibration process to improve model accuracy. Based on the estimated bed elevation, we introduced an index of relative terminus stability, calculated as the ratio between the height of the ice cliff at the calving front and the water depth at the glacier terminus. Our results show a good performance of model, with a mean RMSE of 77.5 m and correlations >0.89 between observed and modeled ice thickness. Perito Moreno glacier shows ice thickness ranging from 200 to 700 m along its centerline, from the calving front to 15 km upstream. It also displays a stability index four times higher than the other two glaciers, which may explain its relatively stable behavior. In contrast, the Upsala and Viedma glaciers exhibit much thicker ice both at the terminus and higher elevations, with stability indexes close to floating near the calving front. We found that retreat rates of 200 m a−1, coupled with thinning rates of 10 m a−1, can propagate the close to floating conditions of the ice up-glacier. The Upsala and Viedma glaciers have reached these values, which can account for their rapid mass loss. Our results and methodology contribute to the understanding and monitoring of calving glaciers´ stability in the region.