Testing time-lapse gravimetry on Murtèl rock glacier (Swiss Alps) to quantify subsurface water/ice storage changes

Seasonal storage of liquid and frozen water in high-mountain catchments will play an increasingly important role as a hydrological buffer in rapidly deglaciating mountains, sustaining streamflow during late-summer dry phases after completion of the snowmelt. Depending on the local topo-climatic conditions, these catchments are (partly) underlain by permafrost. However, below-ground water/ice storage processes, their dynamics, and water pathways are currently poorly characterized. This holds particularly in high-mountain catchments where field data with sufficient resolution to capture the spatial variability are sparse. Among geophysical techniques, time-lapse gravimetry stands out as a method that is directly sensitive to the target quantity, mass (density) distribution changes, at an appropriate spatial scale. Time-lapse gravimetric surveys have successfully quantified groundwater storage changes in high-mountain catchments (Halloran, 2025), but have never been deployed on mountain permafrost, notably rock glaciers.
33 years after pioneering gravimetric investigation on Murtèl rock glacier (Vonder Mühll & Klingelé, 1994), we return to the site with a state-of-the-art relative spring gravimeter (Scintrex CG-6 Autograv) able to resolve water/ice storage changes at the few μGal range (corresponding to <10 cm water equivalent). First, we present results from repeat gravimetric surveys, complemented by drone-based photogrammetry, that we carried out in early and late Summer 2024. We observed significant, spatially variable gravity changes attributable to the seasonal ice loss in the coarse blocky active layer. Second, we compare our data with the 1991 measurements (Vonder Mühll & Klingélé, 1994). Finally, we discuss the strengths and limitations of time-lapse gravimetry in complex mountain permafrost terrain, including challenges related to the decomposition of the temporal gravity signal to different water and rock mass distribution changes.

References
Vonder Mühll, D. S., and Klingelé, E. E.: Gravimetrical investigation of ice-rich permafrost within the rock glacier Murtèl-Corvatsch (upper Engadin, Swiss Alps). Permafrost and Periglacial Processes, 5(1), 13–24. doi:10.1002/ppp.3430050103, 1994.
Halloran, L.J.S., Mohammadi, N., Amschwand, D., Carron, A., Gutierrez, F., Baia Sampaio, J., and Arnoux M.: Hydro-gravimetry as a monitoring solution for water and ice storage changes in dynamic alpine environments, EGU General Assembly 2025, Vienna, Austria, 27 April–2 May 2025, EGU25-3101, 2025.