Accumulation by avalanches as a significant contributor to the mass balance of a peripheral glacier of Greenland

Abstract. Greenland's peripheral glaciers are losing mass at an accelerated rate and are contributing significantly to sea level rise, but only a few direct observations are available. In this study, we use the unique combination of high-resolution remote sensing data and direct mass balance observations to quantify the contribution of a singular avalanche event to the mass balance of Freya Glacier (74.38° N, 20.82° W), a small (5.5 km2, 2021) mountain glacier in Northeast Greenland. Elevation changes calculated from repeated photogrammetric surveys in August 2013 and July 2021 show a high spatial variability, ranging from −11 to 18 m, with a glacier-wide mean of 1.56 ± 0.10 m (1.33 ± 0.21 m w.e.). After applying a seasonal correction of −0.6 ± 0.05 m w.e., the geodetic mass balance over the entire 8-year period (2013–2014 to 2020–2021) is found to be 0.73 ± 0.22 m w.e. A significant influence over the near-decadal mass balance stems from the exceptional winter mass balance of 2017–2018, which was 2.5 standard deviations above average (1.89 ± 0.05 m w.e.). After heavy snowfall in mid-February 2018, snow avalanches from the surrounding slopes affected more than one-third of the glacier surface and contributed 0.35 ± 0.04 m w.e., which is close to 20 % of the total winter mass balance of 2017–2018. Remote sensing data show that Freya Glacier is also prone to avalanches in other years but to a lesser spatial extent. Due to a gap in mass balance point observations caused by high accumulation rates (buried stakes) and the COVID-19 pandemic, the recently reported glacier-wide annual mass balances are rather crude estimates and show a negative bias of −0.22 m w.e. a−1 compared to the geodetic mass balance. Finally, we speculate that the projected future warming may increase the likelihood of extreme snowfall, thus potentially increasing the contribution of snow avalanches to the mass balance of mountain glaciers in Northeast Greenland.