Understanding the mechanical destabilization of large permafrost rock slope failures using data, samples and models from the Bliggspitze 2007, Fluchthorn 2023 and Kleines Nesthorn/Blatten 2025 failures

This paper discusses mechanical modelling strategies for instable permafrost bedrock. Modelling instable permafrost bedrock is a key requirement to anticipate magnitudes and frequency of rock slope failures in a changing climate but also to forecast the stability of high-alpine infrastructure throughout its lifetime.  

The last 5-10 years have brought upon significant advances in the (i) knowledge of relevant hydrostatic pressures in permafrost rock, (ii) the brittle-ductile transitions of ice relevant for larger permafrost rock slope failures and (iii) techniques that can help to decipher the preparation phase of large rockslides also (iv) many new examples have delivered additional insight into multi-phase failure.

Degrading permafrost will act to alter (i) rock mechanical properties such as compressive and tensile strength, fracture toughness and most likely rock friction, (ii) warming subcero conditions will weaken ice and rock-ice interfaces and (iii) increased cryo- and (iv) hydrostatic pressures are expected. This paper presents data and strategies how to obtain relevant (i) rock mechanical parameters (compressive and tensile strength and fracture toughness, lab), (ii) ice- and rock-ice interface mechanical parameters (lab), (iii) cryostatic forces in low-porosity alpine bedrock (lab and field) and (iv) hydrostatic forces in perched water-filled fractures above permafrost (field).

This contribution will focus on three recent events, the Bliggspitze 2007, the Fluchthorn 2023 and Kleines Nesthorn/Blatten 2025 rock slope failures which have provided significant new insights in the mechanics of premafrost rock slope detachment, due to novel observational data, lab results and resulting mechanical models.