Seasonal Velocity Variations of Pra Sec Glacier (Mont Blanc Massif). Detection and Analysis by Optical Satellite Sensors and UAV

The Pra Sec glacier is located in Val Ferret, a highly glacierized valley on the Italian side of the Mont Blanc Massif. Due to its geomorphological setting this area is extremely exposed to glacial-related risks and, over the last decade, a wide array of monitoring systems has been set up to follow the evolution of the Whymper hanging glacier and the Planpincieux glacier [1]. However, in order to expand the current knowledge over other glaciers of the Val Ferret, we began a basin-scale analysis of glacier surface displacements based on Sentinel-2 optical imagery. The methodology applied for the glacier velocities extrapolation has proved to be ineffective over very small glaciers (<250 m wide) but highlighted very unusual high velocity peaks on other glaciers. For the Pra Sec Glacier, analysis of the very high resolution (VHR) optical images confirmed the trends observed with Sentinel-2 imagery. Moreover, Unmanned Aerial Vehicle (UAV) surveys revealed high displacement rates and strong ice avalanche activity from the glacier front, indicating the need to plan future specific monitoring activities as the slopes below the Pra Sec glacier host a road and a village.