EGU21-5908
https://doi.org/10.5194/egusphere-egu21-5908
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

High alpine rock-wall retreat rates over millennia through thermo-cryogenic pre-conditioned rock fall (Mt. Eiger, Switzerland)

David Mair1, Alessandro Lechmann1, Romain Delunel1, Serdar Yeşilyurt1,2, Dmitry Tikhomirov1,3, Christof Vockenhuber4, Marcus Christl4, Naki Akçar1, and Fritz Schlunegger1
David Mair et al.
  • 1Institute of Geological Sciences, University of Bern, Bern, Switzerland (david.mair@geo.unibe.ch)
  • 2Department of Geography, Ankara University, Ankara, Turkey
  • 3Department of Geography, University of Zurich, Zurich, Switzerland
  • 4Laboratory of Ion Beam Physics, ETH Zurich, Zurich, Switzerland

Rock fall processes of various size and magnitude control retreat rates of high alpine rock-walls. For millennial time scales, these retreat rates can be quantified in-situ from concentrations of cosmogenic nuclides along bedrock depth profiles (Mair et al., 2019). We measured cosmogenic 36Cl and 10Be along several such profiles at Mt Eiger in the Central Swiss Alps to study the local rock-wall retreat on this time scale (Mair et al., 2019; 2020). The resulting spatial pattern shows that rock-wall retreat rates are low (0.5 to 0.6 ± 0.1 mm/yr) in the higher region of the NW rock-wall, in contrast to both the lower part of the NW rock-wall and the SE face, where rates are high (1.7 ± 0.4 to 3.5 ± 1.4 mm/yr). We link these retreat rates to differences in local temperature conditions, because the patterns of faults and fractures and the lithology of the bedrock are similar at all sites, and thermo-cryogenic processes are known to weaken the bedrock through fracturing, thereby preconditioning the occurrence of rock fall (e.g., Draebing and Krautblatter, 2019). However, it is still unclear how effective and at which rate individual thermo-cryogenic processes contribute to the preconditioning through fracturing. Therefore, we investigate several processes and estimate the probability of bedrock fracturing through the employment of a theoretical frost-cracking model, which predicts cracking intensity from ice segregation. The model results infer a low efficiency in the higher region of the NW rock-wall, but a relatively high one in the lower section of the NW wall and on the SE rock face of Mt. Eiger. Although the model is rather generic, the results disclose a significant control of temperature conditions on the erosional processes and rates. Furthermore, temperature conditions for the last millennia have been similar to present day conditions, as our reconstructions disclose, therefore the cosmogenic-nuclide-based long-term differences in rock-wall retreat rates predominantly stem from large contrasts in the microclimate between the NW and SE walls of Mt. Eiger. Accordingly, the site-specific differences in microclimate conditions could explain the lower retreat rates in the upper part of the NW rock-wall and the rapid retreat in the SW face and in the lower part of the NW rock face.

References

Draebing, D. and Krautblatter, M.: The Efficacy of Frost Weathering Processes in Alpine Rockwalls, Geophys. Res. Lett., 46, 6516–6524, doi:10.1029/2019GL081981, 2019.

Mair, D., Lechmann, A., Yesilyurt, S., Tikhomirov, D., Delunel, R., Vockenhuber, C., Akçar, N. and Schlunegger, F.: Fast long-term denudation rate of steep alpine headwalls inferred from cosmogenic 36Cl depth profiles, Sci. Rep., 9, 11023, doi:10.1038/s41598-019-46969-0, 2019.

Mair, D., Lechmann, A., Delunel, R., Yeşilyurt, S., Tikhomirov, D., Vockenhuber, C., Christl, M., Akçar, N. and Schlunegger, F.: The role of frost cracking in local denudation of steep Alpine rockwalls over millennia (Eiger, Switzerland), Earth Surf. Dyn., 8, 637–659, doi:10.5194/esurf-8-637-2020, 2020.

How to cite: Mair, D., Lechmann, A., Delunel, R., Yeşilyurt, S., Tikhomirov, D., Vockenhuber, C., Christl, M., Akçar, N., and Schlunegger, F.: High alpine rock-wall retreat rates over millennia through thermo-cryogenic pre-conditioned rock fall (Mt. Eiger, Switzerland), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5908, https://doi.org/10.5194/egusphere-egu21-5908, 2021.

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