Rapid regional assessment of rock glacier activity based on DInSAR wrapped-phase signal

Abstract. Alpine periglacial landforms like rock glaciers and protalus ramparts are key indicators of the state of permafrost. They are characterized by complex deformation mechanisms and temporal trends, possibly evolving towards destabilization. A quantitative assessment of their activity is thus fundamental in climatological and geohazard perspectives. Spaceborne interferometric synthetic-aperture radar (InSAR) techniques provide powerful tools to document the surface deformations of periglacial features, yet their application to the rapid screening of rock glacier activity over wide areas is still limited. We propose a semi-automated methodology that combines wrapped-phase deformation signals obtained from differential interferometric synthetic-aperture radar (DInSAR), available information on permafrost extent, geomorphological data, and multivariate statistics to characterize the activity of 514 periglacial landforms over 1000 km2 in Upper Valtellina (Central Alps, Italy). We process Sentinel-1 A and B SAR images with increasing temporal baselines (12 to 120 d) to generate 124 interferograms in ascending and descending geometries. We analyse the statistical distribution of the wrapped interferometric phase to assess the state of activity of each periglacial landform through an objective activity index. This is combined with regional-scale information on the likelihood of permafrost occurrence to classify periglacial landforms based on their activity on different temporal scales. We obtain four activity classes, validated by comparison to geomorphological evidence and related to environmental variables through multivariate statistics. Our results demonstrate the potential of wrapped DInSAR products, routinely generated over large areas and unaffected by unwrapping errors, to support a regional-scale screening of periglacial landform activity and the identification of candidates for site-specific studies.