Abstract:
Prof. Miriam Dühnforth, Dept. of Earth and Environmental Sciences, LMU Munich

Advances and retreats of alpine glaciers over glacial-interglacial cycles have strongly influenced the evolution of alpine landscapes and have led to variations in the patterns and rates of sediment erosion and transport. I will present case studies from the western United States to show how glaciers erode the landscape and to demonstrate the variability of sediment transport outside of the glacial footprint through time. Lithologic properties such as the degree of fracture spacing and rock type exert a strong control on the efficiency of glacial erosion processes during glacial times. For example, the broader the fracture spacing, the lower are the rates at which a glacier can erode blocks from its bed. We suggest that the lack of cracking in granitic rocks makes subglacial erosion less efficient, leading to a characteristic landscape with smoothly polished bedrock surfaces and granitic domes. The amount of glacial erosion also dictates how much sediment is fed into the fluvial system at the glacier terminus. We dated the timing of sediment export from glaciated catchments to the range-bounding basin, and show that sediment aggradation and incision are tightly linked to times of high sediment supply during glacial times. But we also demonstrate that local conditions in the source area such as the sediment storage capacity of individual catchments, set by the results of glacial erosion processes, can significantly control the export of sediment to the adjacent basin.