Recent evolution of high Alpine areas: multi-sensor optical satellite imagery analysis in the Monte Rosa massif, Western Alps

Abstract In recent years, both mountaineers and researchers have documented an increased degradation of high-altitude glacierized areas, leading to processes such as permafrost thawing, increased rockfall activity and expansion of rock outcrops. Pilot studies have been performed, but data from different massifs and regions are needed to better understand these phenomena. To study the evolution of these high-altitude areas, we mapped rock bodies using remotely sensed data. Analysis of rock outcrop areas have been performed between 2017 and 2022. Semi-automatic classification of free-access Sentinel-2 (10 m resolution) images and manual digitization on commercial Pléiades (0.5 m resolution) imagery has been compared. Our study shows an increase in rock outcrop areas in high-altitude environments. Both datasets show similar results coherent with literature data. Thanks to the higher resolution of the Pléiades dataset, resulting in a superior accuracy of the analysis, out of a total analyzed area of 28.09 km 2 , the areas of rock outcrops increase by 10% in 5 years. The feasibility of using medium-resolution multispectral imagery to document the aforementioned geomorphological process has proven effective in showing the very fast shrinking of glacial areas during the study period. Even though the high-altitude portions of large glaciers do not show significant local mass loss in the accumulation areas, the adjacent areas showed important areal changes in the present climate change context. We conducted our study in a pilot area, where field observations indicated a probable fast evolution of degradation processes. Still, an extension to a regional scale is needed to better define those dynamics and their recent evolution. A possible exacerbation of the processes due to the warm summer of 2022, which falls within the study period, has to be considered. Furthermore, the evolution in the next decades still has to be monitored to confirm a specific trend. High mountain processes of the Alpine environment, such as the one outlined in the present study, have to be better observed and understood. Nevertheless, our work shows that rapidly evolving trends exist and should be monitored.