Monthly velocity and seasonal variations of the Mont Blanc glaciers derived from Sentinel-2 between 2016 and 2024

Abstract. We investigated the temporal variability of the surface velocity of 30 glaciers in the Mont Blanc massif (European Alps). We calculated the monthly velocity between 2016 and 2024 using digital image correlation of Sentinel-2 optical imagery. The main objectives of the study were (i) to characterize the variability of the velocity fields of such glaciers (referring to both their temporal seasonal and inter-annual and spatial variations) and (ii) to investigate relationships between the morphology of glaciers and their kinematics. We measured monthly velocities varying from 12.7 to 487.4 m yr−1. We observed an overall decrease in the velocity between 2016 and 2019 and an unexpected rise in 2020–2022, which are especially visible in most glaciers on the southern side of the massif. Considering the whole period, half of the glaciers showed positive acceleration, which reached values > 4 m yr−2 in three glaciers. In general, the trend's absolute value in the cold season is higher in the case of positive acceleration and lower in the case of negative acceleration. We found that smaller glaciers have a more pronounced seasonality, with winter–summer velocity differences of 50 %–100 %. Finally, in 2016, 2018, and 2022, we observed an exceptionally high winter–summer velocity difference in the 0.3 km2 wide Charpoua Glacier, when summer velocities increased by 1 order of magnitude.