Abstract ID: 28.7282 | Accepted as Talk | Talk/Oral | 2025-02-28 15:00 - 15:15 | Ágnes‐Heller‐Haus/Small Lecture Room

Avalanches are important contributors to the surface mass balance of glaciers. For the case of Argentière Glacier, a recent study using an approach combining remote sensing and modelling showed that they contribute to 20% of its overall accumulation, and up to 60% at the base of its north-facing headwalls. These high accumulation rates indicate a large mass turnover on avalanche deposits, which should therefore be considered as key locations of glacier mass input. However, given the challenges to monitor these specific locations (avalanche risk for persons and instruments, steep slopes), the spatio-temporal variability of mass accumulation, submergence, compaction or ablation has never been directly quantified at such locations. Here we present the first results of 2 years of measurements on one of the largest avalanche deposits of the accumulation zone of Argentière Glacier. The measurements consist of weekly Digital Elevation Models derived from an array of time-lapse cameras, along with UAV LiDAR and photogrammetry surveys, surface mass balance and 3D velocity measurements at stakes, snow density profiles, Ground Penetrating Radar (GPR) profiles of snow depth and terrestrial LiDAR surveys conducted over 10 field visits (76 person-days) from November 2022 to October 2024. The avalanche deposit presents the shape of a large cone (~500 m wide and ~200 m tall) at the base of a steep ~600 m couloir where most of the gravitational snow redistribution originated from, and is bordered by steep rocky ridges. We observed strong thinning (between June and October) and thickening (between October and May) patterns, with amplitudes close to 50 m below the bergschrund, which we could link to a high spatial variability in mass accumulation and ice submergence. This resulted in a flattening of the top part of the cone during the summer months, which in turn influenced the patterns of snow deposition by avalanching. Overall, we estimate the mass accumulation from avalanching to represent 50-70% of the total accumulation at this location, with a very strong spatial variability.