| Résumé: |
By means of subglacial processes such as abrasion and quarrying, Alpine glaciers actively erode the underlying bedrock and mobilize large amounts of sediments. Glacial erosion rates are commonly linked to basal sliding and rock erodibility, but precise controls on its spatial variability and short-term dynamics within a glacier are yet to be robustly constrained. Here we determine the provenance of zircon grains found suspended in the proglacial stream using an inversion approach to establish spatial patterns of erosion below a glacier and their evolution in time via repeated sampling throughout the early melting season. We focus on the Gornergletscher glacial system (Swiss Alps), which is one of the fastest fast-flowing glaciers in the Alps. It is also rapidly retreating in response to global warming. Thereby, we generate time-series of erosion maps, which are presented here in hourly resolution for two days during summer 2019. The inferred erosion maps show that sediment delivery during the early melting season is strongly influenced by the sudden activation of sediment supply zones, and that erosion rates evolve throughout the day along with discharge. Areas that were recently exposed by the glacier's retreat appear to be major erosion sources, and their signal is clearly dominant over that of glacial erosion for the concerned spatial units. |
Mémoire [34 Mo]