Spatio-temporal dynamics of glacial erosion in high Alpine catchments

The impact of glaciation leaves a distinct signature in mountain landscapes. These high relief environments, with heterogeneous long-profiles comprised of complex features and landforms like large topographic steps, overdeepened basins and adverse slopes, are unique to the influences of glacial erosion and differ markedly to fluvial landscapes. Complex topography within high alpine catchments occupied by today’s glaciers is suggestive of strong spatial variability in the efficacy of glacial erosion, yet the specific rates and reasons behind this remain poorly understood and raise questions regarding the role of glacial erosion in balancing tectonic uplift to maintain topographic steady-state. A novel inventory of contemporary icefalls in upper catchments across Switzerland is compiled which shows a strong correlation to climate gradients, suggestive of a disconnect in regions of effective erosion over time and signifies their potential importance in the long-term landscape evolution of glacial catchments. A numerical landscape evolution model is then used to explore the spatio-temporal variability of glacial erosion under different climate conditions and to test the impact of different numeric erosion laws. The pre-existing topography and positioning of the catchment in the wider basin is found to be a dominant control on the patterns and rates of glacial erosion, which has the potential to differ significantly between glacial and interglacial states or to remain relatively similar depending on catchment characteristics. Choice of erosion law also has a substantial impact on the strength of erosion occurring across the catchment and demonstrates the need for improved empirical constraints. Finally, a unique method of luminescence thermochronometry is applied to bedrock samples from the field to derive a novel time-series of exhumation rates spanning the past 100 ka, which is used to infer patterns of glacial erosion that broadly agree with the modelled outcomes. Collectively, high alpine catchments are shown to be highly dynamic and as regions of longest ice residency time, are responsible for maintaining a long-term dynamic equilibrium of the landscape through orders of magnitude changes in erosion according to topographic features and climate conditions.