Time-lapse gravimetry (TLG) is a non-invasive, integrative, geophysical/geodetic method in which changes in g can be measured to parts-per-billion precision. Measured gravity changes are, in part, the result of water/ice storage changes. Thus, TLG can be a powerful tool for the monitoring of the two hydrological components of alpine systems that are the most difficult to quantify: ground ice and groundwater.

We recently carried out the first periglacial application of TLG. At the well-known Murtèl rock glacier (Graubünden, Switzerland), we measured seasonal gravity changes in the July to September period and used UAV photogrammetry to correct for the effect of snow mass. Our results reveal spatial variations in active layer thaw (11 to 64 cm water equivalent) that would be challenging to observe directly. Comparison of our high precision data with a historic gravimetry survey also suggests the occurrence of permafrost degradation over the past three decades.

At other Alpine sites, we have employed TLG to monitor groundwater storage recession during the summer/autumn snow-free period. The gravimetry data provide quantitative insights into groundwater storage that would typically require extensive borehole infrastructure to obtain. TLG is a unique and effective method for quantifying subsurface storage variations and is particularly well-suited for alpine regions due to their pronounced annual hydrological variability and insufficient subsurface monitoring.