Mountain permafrost is currently undergoing major changes showing clearly detectable ground temperature increase and ground ice content loss. On regional scales, it becomes standard to quantify ground ice loss through electrical, seismic and electromagnetic techniques. Recently developed joint inversion approaches combining different tomographic techniques allow for ground ice loss quantification over time (Steiner et al. 2021, Morard et al. 2024).

The recently funded TREAT project addresses current research questions regarding the future evolution of mountain permafrost such as the existence of tipping points causing irreversible permafrost degradation, the influence of anomalously hot periods (Hauck & Hilbich 2024), the resilience of coarse-blocky substrates to warming events and whether thawing permafrost slopes become wetter or drier in future. Consequently, we further develop geophysical joint inversion techniques and numerically couple a thermo-hydraulic permafrost model to geophysical monitoring data from several observatories in the Alps (Maierhofer et al. 2024). First results of the project and potential paths for future research will be presented.

Hauck C & Hilbich C (2024). Preconditioning of mountain permafrost towards degradation detected by electrical resistivity. Environ.Res.Lett. 19 064010; DOI10.1088/1748-9326/ad3c55

Maierhofer T, Flores Orozco A, Roser N, Limbrock JK, Hilbich C, Moser C, Kemna A, Drigo E, Morra di Cella U & Hauck C (2024). Spectral induced polarization imaging to monitor seasonal and annual dynamics of frozen ground at a mountain permafrost site in the Italian Alps, The Cryosphere, 18, 3383–3414, https://doi.org/10.5194/tc-18-3383-2024

Morard S, Hilbich C, Mollaret C, Pellet C & Hauck C (2024). 20-year permafrost evolution documented through petrophysical joint inversion, thermal and soil moisture data. Environ.Res.Lett., 19; 074074, DOI10.1088/1748-9326/ad5571.

Steiner M, Wagner FM, Maierhofer T, Schöner W & Flores Orozco A (2021). Improved estimation of ice and water contents in Alpine permafrost through constrained petrophysical joint inversion: The Hoher Sonnblick case study. Geophysics, 86(5), WB61-WB75.

Joints and fractures, where large volumes of ground ice can accumulate, play a key role in the thermal regime of bedrock permafrost as they represent a preferential flow path for water and advective heat exchange between the atmosphere and the subsurface. Yet, it is challenging to include them in thermal modelling because their exact location and geometry are commonly unknown. In the Cime Bianche (Aosta valley, Italy) permafrost monitoring area (highly weathered bedrock plateau) at 3100 m a.s.l. borehole temperature measurements and geophysical imaging have shown a high spatial variability in ground temperature and ice content, which suggests the presence of fractured areas affecting the ground thermal regime. We conducted saltwater tracer tests (30-100 l water per injection) at eight different locations at the Cime Bianche site coupled with time-lapse 3D electrical resistivity tomography (ERT) to track the flow of the subsurface amendment and localize flow paths associated to fractured areas. The ERT results show a large difference in flow characteristics between the injection points, even for points in close vicinity (few meters). In five of eight injection points the water infiltrated slowly into the subsurface (over 2-3 hours) resulting in slight conductivity changes over time in the 3D ERT images only close to the injection point. In the other three positions the injected water disappeared after a few seconds resulting in larger conductivity changes, not only directly below the injection point but also to a depth of >10 m, suggesting the presence of fractures. These results demonstrate that our methodology is able to reveal fractures and other preferential flow paths. To further improve the resolution of the resolved fractures more adequate inversion schemes and constraints from complementary data are required.