ALBERT

Description: Greenland´s peripheral glaciers are losing mass and are contributing significantly to sea level rise. As direct observations are scarce our knowledge is mainly based on remote sensing studies, that can hardly identify individual processes. Here, we use the unique combination of remote sensing data and direct observations to quantify the effect of avalanches on the mass balance of Freya Glacier, a small (5.3km²) coastal valley glacier in Northeast Greenland with direct mass balance observations since 2007. We calculate elevation changes and geodetic mass balance of Freya Glacier from repeated high resolution photogrammetric surveys in 2013 and 2021 using a structure from motion workflow. Elevation changes between 18.8. 2013 and 28.7.2021 range from -10 m to +16 m, with an overall mean of +1.5 m. Seasonal mass balance observations show, that the overall positive mass balance is mainly due to the exceptional winter accumulation of 2018 when in addition avalanche deposits affected 1/3 of the glacier area. Areas of high positive elevation changes correspond to avalanche deposits of 2018 and 2016. The traditional stake network is not dense enough to resolve the spatial variability of the observed elevation change pattern. A first comparison shows, that the glaciological glacier-wide mass balance is more negative than the geodetic one. In this study we analyse possible sources for this discrepancy and quantify the uncertainties of both methods.