Alpine landslide dynamics and post-glacial topographic reshaping

In steep alpine environments, successive glacial-interglacial cycles during the Quaternary led to multiple transient geomorphological phases. These periods are marked by landscape disequilibrium between the inherited topography and the dominant geomorphological processes. In particular, post-glacial periods are key transition phases experiencing rapid geomorphic changes, characterized by intense hillslope processes where ice and permafrost have shrunk. As landslides are the main post-glacial processes controlling sediment production in steep mountain environments, we approach numerically their late-glacial to interglacial dynamics in re-shaping the alpine topography. In the Ecrins massif (French western Alps), we select three catchments, with particular morphological signatures (i.e. from fluvial to glacial) to explore their associated topographic evolution under landsliding. Using the landscape evolution model ‘Hyland’, we quantitatively assess their individual response to landsliding by exploring the role of different internal or external factors (e.g., bedrock cohesion, return time of landslides). The model is calibrated with the output landslide area-volume scaling law and the massif-averaged denudation rate, known from literature. We focus on the cumulative impact of landslides, during the post-glacial period, on catchment slope distribution, hypsometry, produced sediment volume and erosion rate. Moreover, inherited glacial topography seems strongly sensitive to hillslope processes showing a bimodal distribution of elevation for landsliding for the glacial catchments, both spatially and temporarily. The evolution of the slope-elevation distribution is associated to a lowering in maximum catchment elevations, usually attributed to the glacial buzzsaw. Our modeling results also show a temporal variability in landslide frequency, highlighting a maximum frequency at the onset of the glacial retreat followed by a progressive decay during the interglacial period, despite an inherent variability associated with landslide stochasticity. Thus, the associated landslide erosion rate follows a similar progressive trend. On the contrary, fluvial catchments show more stable topography and less intense landslide activity. Landscape evolution models appear as a suitable tool to reveal the landslide dynamics during the postglacial period and to quantitatively explore the non-linear interactions between landsliding and catchment topographic evolution.