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 occurrence and its climatic implications. These landforms are characterized by complex deformation mechanisms and temporal trends, that can evolve towards destabilization. A quantitative evaluation of their activity is thus fundamental in climatological and geohazard perspectives. Spaceborne interferometric synthetic-aperture radar (InSAR) techniques have provided powerful tools to document the surface deformations of periglacial features, yet their rapid and reliable application over large areas is still limited.

We propose a novel, 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 approximately 1000 km² in Upper Valtellina (Italian Central Alps). We process Sentinel-1 A/B SAR images with increasing temporal baselines (12 to 120 days) to generate 124 interferograms in ascending and descending geometries. We analyse the statistical distribution of 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 permafrost occurrence to classify periglacial landforms based on their activity on different temporal scales. We define four activity classes, validated with field geomorphological observations, and related to their environmental controls through multivariate statistical analysis. Our results demonstrate the potential of using wrapped SAR interferometric phase to rapidly update periglacial landform inventories and track the evolution of the alpine cryosphere.