Rock-slope response to deglaciation: sudden or delayed failure?

Past and ongoing phases of climate change caused the retreat of numerous glaciers and the onset of slope instability of deglaciated rock slopes, with major implications for landscape evolution and geohazard. Several studies have demonstrated that slope debuttressing and hydro-mechanical perturbations associated to deglaciation promote "paraglacial" progressive slope failure. Large rock slope failures with different styles of activity have been observed during, soon after or thousands of years after deglaciation. Moreover, not all the paraglacial rock slope failures differentiate into large rockslides potentially evolving to destructive catastrophic failure. However, there is a debate on the factors that control the timing of paraglacial slope failures, and their mechanisms remain elusive.

We investigated the mechanisms and timing of large rock slope response to deglaciation using the 2D FEM model DaDyn-RS, which integrates damage and time-to-failure laws to provide an explicitly time-dependent description of damage accumulation, strain localization and hydro-mechanical coupling resulting in slope creep (i.e. time-dependent deformation). We simulated realistic, non-linear deglaciation histories derived from a 3D glaciation-deglaciation model (ICE-CASCADE) based on Stokes solutions of the ice flow. We performed a parametric study systematically exploring the effects of valley shape, rock strength, initial ice thickness and deglaciation rate on the mechanisms, onset timing and long-term evolution of paraglacial rock-slope failures. Our modelling results, constrained using field data, point out the conditions associated to sudden or delayed failure and the scenarios more prone to landslide evolution to catastrophic failure.