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 an 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 (bedrock cohesion and friction, return time of landslides). The model is calibrated with the output landslide area-frequency 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, exported sediment volume and erosion rate. Compared to a fluvial landscape, the inherited glacial topography shows a bimodal distribution of elevation for unstable slopes, near the crests and along the U-shaped 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. Despite the stochastic nature of landslides, our modeling results also show that landslide activity and induced erosion rates are greatest at the onset of the glacial retreat and then progressively decay during the interglacial period. In contrast, fluvial catchments show a more stable topography and fewer landslides resulting in lower erosion rates. This study quantitatively explores the non-linear interactions between landslides and catchment topographic evolution and documents the role of landslides in the erosion pulse during the Quaternary interglacial periods.