Water and Ice-related thermo-mechanical processes in the fractures of Steep alpine bedrock Permafrost – WISPER

Methods encompass numerical modeling coupling thermal and hydrological processes. New modeling approaches must be developed to apply these models to high mountain rockwalls. These new models also intend to contribute to the parameterisation of mechanical models. Finally, in parallel of the numerical develoments, In addition, energy balance models have to be developed to to quantify the water that could infiltrate into the rockwalls. Finally, in parallel of the numerical models, geophysics, and notably geoelecrtical soundings are used to gain independant data to evaluate those models.

The first coupled thermal and hydrological models have been developed and are being published. A set of geoelecrtrical soundings have been acquired and the first data have been acquired. Geoelectrical data processing will start during winter 2021/2022.

Perpectives of this project are of several orders:
- simulate thermo-hydro-mechanical processes at recently observed rockfalls to understand there triggering processes
- generalise this understanding to better apprehend areas and periods «at risk«
- offer new insights into the understanding of alpine landscape developments, notably into the assymetry between north and south faces.

4 communcations in international congresses, 2 publications into international journals with peer-review (1 being published, accepted in september 2021).

WISPER intends to link thermal, hydric and mechanical processes related to water circulation and icing in the fractures of permanently frozen (permafrost) rock walls to address, (i) permafrost degradation processes and (ii) the increasing rock fall hazards affecting mountain areas. Permafrost degradation is attributed to two main processes: (i) the slow heat conduction from the surface through the saturated rock media, and (ii) the water infiltration and circulation in the farctures acting as a shortcut between the surface and the subsurface. Frozen bedrock failures are attributed to two main processes: (i) the ductile-brittle rupture of warming ice-filled fractures, and (ii) the hydraulic-induced strains. While thermal and mechanical dynamics of saturated and homogeneous (no fractures) frozen rock walls have been investigated since about a decade, hydric processes remain the main barrier to lift to quantitatively interpret and predict permafrost degradation and failure mechanisms. These processes have been so far neglected by rock wall permafrost investigations because of (i) their complexity which involves non-linear thermal and mechanical patterns and (ii) the lack of available data to parameterize and evaluate numerical models.
WISPER will tackle this main scientific gap by implementing three work packages (WP) which involve development of innovative numerical modelling procedures and geophysical soundings. It will gather skills, tools and data from four institutes spread between France (EDYTEM Lab. and ISTerre Lab. from CNRS and Université Savoie Mont Blanc), Germany (Technical University of Munich) and Norway (University of Oslo). In the 1st WP (WP1), the unique dataset already collected in the Mont Blanc massif (notably high resolution digital elevation models, > 10 years of rock falls inventory, bedrock temperature, climate variables and fracture kinematics time series) will be used to develop hydro-thermal models, and provide relevant data to parameterize mechanical models in the 3rd WP (WP3). In parallel, cutting-edge geophysical measurements and monitoring will be performed on pilot-sites to image the fractures content and saturation (WP2) and to gain an independent dataset to parameterize and evaluate the numerical models intended in WP1 and WP3. The combination of the three WPs will allow a better theoretical understanding of the thermal dynamics and mechanical behavior of frozen rock walls.
About 260 k€ are demanded to cover non-permanent staff costs (Postdocs and Interns), numerical and geophysical equipment, travelling fees for results dissemination and field work, and publication costs. This project is based on already setup national and international collaborations, is aligned with the coordinator’s background, and will allow reinforcing her position as a leading scientist in high mountain permafrost researches. This project will deliver new numerical models, sensitivity analyses and ground properties images relevant for the research community focusing on steep slopes morphodynamics and cryospheric processes on the short to medium term. Furthermore, on the medium to long term, the delivered results will be a solid basis to draw research directions towards operational solutions to anticipate and mitigate the risks associated to deglaciating environments, which is of primary interest for land planners, policy makers and mountain professionals (e.g. mountain guides). The results will be disseminated via high-ranking international scientific journal, national and international scientific conferences, university courses, public media, and training of mountain professionals.