Investigating seasonal and multi-decadal water/ice storage changes in the Murtèl rock glacier using time-lapse gravimetry

Abstract. Rock glaciers are important features of many alpine hydrological systems. Although their seasonal release of water enhances the resilience of alpine headwater catchments to climate change, measurement of their internal water and ice storage changes remains a challenge. Recent technological and methodological advances have enabled novel applications of time-lapse gravimetry (TLG) to estimate subsurface storage changes. Here, we present the first application of TLG on a rock glacier. We measure seasonal (July–September) changes in gravity at the Murtèl rock glacier (Upper Engadine, Switzerland). We employ drone-based photogrammetry to correct for surface mass changes in the form of snow. We also compare the Bouguer anomaly of our 2024 surveys with those from a pioneering 1991 gravimetry study. The seasonal results reveal spatial differences in active layer thaw, with estimated ice storage loss ranging between 11–64 cm water equivalent, while the multi-decadal results suggest zonal decreases in permafrost ice storage. Our study provides new insights into rock glacier–groundwater processes and illustrates how TLG can be employed to measure cryospheric and hydrogeological processes in permafrost and periglacial landforms.