Surface Instability Mapping in Alpine Paraglacial Environments Using Sentinel-1 DInSAR Techniques.

Current climate warming leads to widespread glacier shrinkage in high alpine terrains and associated changes in surface dynamics of deglacierized environments. In consequence, slope instabilities increasingly develop along retreating glaciers through debuttressing effects or degrading permafrost conditions. In the context of associated hazards to the local environment and infrastructure, a thorough analysis of slope instabilities is highly relevant. Affected regions are mostly inaccessible and cover large areas, therefore remote sensing techniques such as differential interferometric synthetic aperture radar (DInSAR) are valuable tools to monitor surface movements and assess their evolution. We apply standard and advanced DInSAR methods using Sentinel-1 SAR data from 2015 until late 2021 to map and classify slope instabilities in three glacierized regions in the European Alps. The final products include an inventory per region, with a total of 815 mapped slope instabilities, of which 38% move <3, 9% move 3–10, 42% move 10–30, and 11% move >30 cm/yr. An additional assessment of four landslides occurring along shrinking glaciers shows time series with recent accelerations in 2018/19. Validation of Sentinel-1 derived slope movement products is performed by comparison with shorter wavelength TerraSAR-X and optical Sentinel-2 derived data using offset tracking. Results clearly show the suitability of Sentinel-1 DInSAR methods to detect a range of slope movements in high alpine terrain, yet also highlight the limitations. We therefore recommend a combination of advanced Sentinel-1 DInSAR and Sentinel-2 offset tracking methods to develop a comprehensive inventory of alpine slope motion.