At the Last Glacial Maximum (LGM), the Rhine Glacier complex (Rhine and Linth glaciers) featured numerous overdeepened valleys as a consequence of repeated glaciations. Their location is close to the LGM ice margin, far in the lowlands, away from the Alps. Numerical models of ice flow of the Rhine Glacier indicate a poor fit between the sliding distance, a proxy for glacial erosion, and the location of these overdeepenings. Calculations of the hydraulic potential based on the computed time-dependent ice surface elevations of the Rhine Glacier lobe obtained from a high-resolution thermo-mechanically coupled Stokes setup of Elmer/Ice are used to estimate the location of subglacial water drainage routes. Results reveal an elevated subglacial water discharge focused along glacial valleys and overdeepenings under the assumption that of water pressure being equal to the ice overburden pressure. These conditions are necessary for subglacial water to remove basal sediments, expose fresh bedrock, and favor further erosion by quarrying and abrasion. Knowledge of the location of paleo-subglacial water drainage routes appears to be a necessary component in understanding patterns of subglacial erosion beneath paleo-ice masses that can not be explained purely by sliding - a fact that also seems to apply to the here studied overdeepenings in the Swiss lowlands.

 

Cohen, D., Jouvet, G., Zwinger, T., Landgraf, A., and Fischer, U. H., 2023. Subglacial hydrology from high-resolution ice-flow simulations of the Rhine Glacier during the Last Glacial Maximum: a proxy for glacial erosion,. E&G Quaternary Sci. J., 72, 189–201, DOI:10.5194/egqsj-72-189-2023