Glacier fragmentation on the Southern Patagonian Icefield: a comprehensive analysis of the Upsala Glacier

Abstract Glacier fragmentation involves the detachment of tributary glaciers from the main glacier trunk and their subsequent fragmentation into smaller units. This reconfiguration, in turn, can lead to a redistribution of stresses and strain rates affecting the dynamics of the glacier. In our study, we examined changes in the frontal position and surface velocity of Bertacchi and Upsala Glaciers using Sentinel-1 derived velocity fields and orthoimages, covering the period between January 2015 and January 2023. Comparison of these results with bed topography and ice thickness datasets indicates that the Bertacchi tributary glacier acted as a strong lateral pinning point for the main flow unit from 2015 to 2018. This slowed its retreat rate to −6 ± 2.5 ma −1 despite the high surface velocity (1825 ± 11 ma −1 ) and buoyancy conditions. However, the loss of this pinning point in early 2019 led to accelerated retreat rates (−325 ± 2.5 ma −1 ) of the western tongue of Upsala Glacier, even though it retreated over a shallow bed and the surface velocity was 45% lower than previous. This retreat was synchronous with the advance of Bertacchi terminus (15 ± 2.5 ma −1 ), suggesting a reduction in the resistive stresses experienced by this glacier following unpinning.