Title: Recent headwall deglaciation and retreat from cosmogenic 10Be in medial moraine debris of a Swiss valley glacier

Katharina Wetterauer1, Dirk Scherler1,2, Leif S. Anderson1,3, Hella Wittmann1

1GFZ German Research Centre for Geosciences, Potsdam, Germany; 2Institute of Geological Sciences, Freie Universität Berlin, Berlin, Germany; 3Institute of Earth Surface Dynamics, University of Lausanne, Lausanne, Switzerland

Event: GeoKarlsruhe 2021

Date: 2021

DOI: 10.48380/dggv-81h6-sn36

Debris-covered glaciers are fed from steep bedrock hillslopes that tower above the ice, so-called headwalls. Recent observations in high-alpine glacial environments suggest that rock walls are increasingly destabilized due to climate warming. An increase in debris delivery to glacier surfaces will modify glacial mass balances, as surface debris cover impacts on the melt behavior of the ice underneath. Consequently, we expect that the response of debris-covered glaciers to climate change is likely linked to how headwall retreat responds to climate change.

As debris is deposited on the ice surface along the sides of valley glaciers it is passively transported downglacier on and in the ice. Where glaciers join it is merged to form medial moraines. Due to the conveyor-belt-nature of glacier ablation zones, debris tends to be older downglacier and, hence, systematic downglacier-sampling of medial moraines holds the potential to assess rates of headwall retreat through time.

In order to quantify headwall retreat rates, we measured the concentration of in situ-produced cosmogenic 10Be in debris samples collected on downglacier profiles along parallel medial moraines from a partly debris-covered Swiss glacier. Our results indicate that indeed nuclide concentrations along the medial moraines vary systematically, being higher for older downglacier deposits and lower for younger upglacier deposits. This variation cannot be explained by additional nuclide accumulation during transport alone. Instead we propose that ongoing ice cover retreat across deglaciating headwalls since the end of the Little Ice Age and the exposure of newly eroding bedrock surfaces may explain recently decreasing 10Be concentrations.

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