Post-glacial reshaping of Alpine topography induced by landsliding

Abstract. In steep alpine environments, successive glacial-interglacial cycles during the Quaternary led to multiple transient geomorphological phases. In particular, post-glacial periods are key transition phases experiencing rapid geomorphic changes, characterized by intense hillslope processes where ice and permafrost have retreated. Mass wasting is the dominant post-glacial process driving sediment production in steep mountain landscapes. However, its role in shaping topography, particularly in comparison to glacial activity—known for its strong deformational impact—remains poorly understood. By integrating numerical modeling with topographic data, we refine our understanding of how mass wasting shapes evolving landscape and influences sediment dynamics. In the Ecrins massif (French western Alps), we select three catchments, with particular morphological signatures or inheritance (i.e. from fluvial to glacial) to model their associated topographic evolution driven by mass wasting. Using the landscape evolution model ‘HyLands’, 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, inferred from literature. We focus on the cumulative impact of landslides, over a single post-glacial period, on catchment slope distribution, hypsometry, produced sediment volume and erosion rate. Compared to fluvial ones, inherited glacial topography shows a bimodal distribution of elevation for unstable slopes, near the crests and along the U-shape valley walls. The time evolution of this distribution is characterized by a decrease in the number of unstable slopes as well as a lowering in maximum catchment elevations induced by landsliding, usually attributed to the glacial buzzsaw. Indeed, glaciers may be not the only agent controlling mountain elevation, as we discussed in this study. Despite the stochastic nature of landslides, our modeling results also show that landslide activity and induced erosion rates are maximum at the onset of the glacial retreat and then progressive decay during the interglacial period. On the contrary, fluvial catchments show a more stable topography and less intense landslide activity resulting in lower erosion rates. This study quantitatively explores the non-linear interactions between landslides and catchment topographic evolution and questions the role of landslides in the erosion pulse during the Quaternary interglacial periods.