EGU General Assembly 2021
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Evaluating the temperature dependence of bedrock hillslope erosion in the Mont Blanc massif using in situ cosmogenic 3He-10Be-14C

Donovan P. Dennis1, Dirk Scherler1,2, Samuel Niedermann1, Kristina Hippe3, Hella Wittmann1, Ludovic Ravanel4, Marissa Tremblay5, Benny Guralnik6, and Maarten Lupker3
Donovan P. Dennis et al.
  • 1German Research Centre for Geosciences (GFZ), Potsdam, Germany
  • 2Freie Universität Berlin, Berlin, Germany
  • 3Dept. of Earth Science, Swiss Federal Institute of Technology (ETH), Zürich, Switzerland
  • 4EDYTEM, CNRS- Univ. Savoie Mont Blanc, Chambéry, France
  • 5Dept. of Earth, Atmosphere, and Planetary Science, Purdue University, West Lafayette, USA
  • 6Technical University of Denmark, Kongens Lyngby, Denmark

The erosion of cold bedrock hillslopes in alpine environments depends not only on rates of frost weathering and accumulated rock damage, but additionally on the removal of the weathered material from the bedrock surface. In the Mont Blanc massif, steep bedrock faces with exposure ages sometimes much older than 50,000 years sit in close proximity to actively-eroding rockwalls, suggesting a more complex relationship between temperature and erosion rates than encompassed by the proposed “frost-cracking window.” Stochastic events like rockfalls and rock avalanches, despite their rarity, contribute a non-trivial proportion of the total sediment budget in alpine permafrost regions, adding to the contribution from background “steady-state” erosion. Employing a methodology based on the combination of in-situ cosmogenic nuclides 3He -10Be-14C, we test the temperature-dependence of high-alpine erosion while taking into account erosional stochasticity.

From cosmogenic 10Be concentrations of amalgamated samples collected on the Aiguille du Midi (3842 m a.s.l.) in the Mont Blanc massif, we find an order of magnitude difference in erosion rate across the peak’s surface. Our preliminary measured erosion rates, ranging between appx. 0.03 mm yr-1 and 1.0 mm yr-1, correlate neither with modern temperature measurements from borehole thermistors, nor with our current estimates of bedrock cosmogenic 3He-derived paleotemperatures. The corresponding cosmogenic 14C/10Be ratios (between 1.70 and 4.0) for these erosion rates indicate that our measurements are not biased by recent stochastic rockfall events. Our current results therefore suggest that on geomorphic timescales, bedrock hillslope erosion rates are not set solely by rates of frost-cracking, but rather by the combined effects of frost-cracking and permafrost thaw-induced rockfalls. These insights are relevant both for short-term monitoring of alpine permafrost and associated geohazards under a warming climate, as well as studies of proposed “buzzsaws” operating on glacial-interglacial timescales.

How to cite: Dennis, D. P., Scherler, D., Niedermann, S., Hippe, K., Wittmann, H., Ravanel, L., Tremblay, M., Guralnik, B., and Lupker, M.: Evaluating the temperature dependence of bedrock hillslope erosion in the Mont Blanc massif using in situ cosmogenic 3He-10Be-14C, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15023,, 2021.

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