GROUNDWATER-RELATED CYCLIC FATIGUE IN ALPINE FRACTURED BEDROCK SLOPES OF THE ALETSCH VALLEY, SWITZERLAND

In the past eight years, an extensive monitoring campaign has been implemented to track surface deformation and monitor subsurface pore pressure in the fractured bedrock slopes close to the tongue of the Great Aletsch Glacier, Switzerland. Evidence of strong (up to 2 cm) cyclic displacements following is observed and attributed to groundwater recharge from snowmelt infiltration. These cyclic components are superimposed on long-term displacement trends in the direction of the valley center (Oestreicher et al., 2021). The potential drivers for such long-term trends are difficult to disentangle and may be related to the elastic ground deformational response, the current glacier unloading (the Great Aletsch glacier currently drops by ~11 m/y in elevation on average), isostatic rebound from the past melting since the Last Glacial Maximum (LGM, around 18ky BP), and hydromechanical fatigue due to cyclic annual variations of the groundwater table elevation. Combining the high-resolution field monitoring data in the Aletsch valley with numerical modeling results, we propose that the last hypothesis may play an important role in such irreversible displacements as observed in the gneissic slopes of the Aletsch Valley.

Oestreicher, N., Loew, S., Roques, C., Aaron, J., Gualandi, A., Longuevergne, L., Limpach, P., & Hugentobler, M. (2021). Controls on spatial and temporal patterns of slope deformation in an Alpine Valley. Journal of Geophysical Research: Earth Surface, 126(12). https://doi.org/10.1029/2021jf006353