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The Cryosphere An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/tc-2019-42
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/tc-2019-42
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 15 Apr 2019

Submitted as: research article | 15 Apr 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal The Cryosphere (TC).

Fracture dynamics in an unstable, deglaciating headwall, Kitzsteinhorn, Austria

Andreas Ewald1, Ingo Hartmeyer2, Markus Keuschnig2, Andreas Lang1, and Jan-Christoph Otto1 Andreas Ewald et al.
  • 1Department of Geography and Geology, University of Salzburg, Salzburg, 5020, Austria
  • 2Georesearch Forschungsgesellschaft mbH, Wals, 5071, Austria

Abstract. Processes destabilising recently deglaciated rockwalls, driving cirque headwall retreat, and putting high alpine infrastructure at risk are poorly understood due to a lack of in situ monitoring data. Deglaciation initiates internal stress redistribution and drastically increases atmospheric forcing rendering cirque headwalls particularly prone for rock slope failure. Here we present quantitative data from an unstable, recently deglaciated cirque headwall. We monitor the dynamics of a fracture at the north face of the Kitzsteinhorn (3203 m a.s.l.) over a period of 2.5 years. Two crackmeters measure horizontal and vertical crack deformation with a resolution of ±0.003 mm and are complemented by crack top temperature measurements. To decipher thermo-mechanical from cryogenic forcing, thermal expansion coefficients for both horizontal and vertical directions are calculated to derive purely thermo-mechanical deformation. Our data shows that fracture dynamics are dominated by thermo-mechanical expansion and contraction of the inter-cleft rock mass during snow-covered and snow-free periods. Significant deviations from thermo-mechanical behavior occur due to freeze-thaw action during spring and autumn zero curtain periods. Exceptional vertical deformation during these periods is triggered by rainfall events providing liquid water into the fracture system. Subsequent refreezing rather than hydrostatic pressure build-up is to the most likely cause of the mechanical response. Lower magnitude horizontal deformation occurs in autumn and early winter due to ice segregation. Irreversible fracture opening was not observed, however, enhanced cryogenic deformation in spring and autumn may lead to shallow, low magnitude rock detachments. Our results highlight the importance of liquid water intake in combination with subzero-temperatures on the destabilisation of glacier headwalls. We conclude that intense frost action and ice segregation are common processes in randkluft systems, serving as important preparatory factors of paraglacial rock slope instability.

Andreas Ewald et al.
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Short summary
Processes destabilising recently deglaciated rocks, driving cirque headwall retreat, and putting alpine infrastructure at risk are poorly understood due to scarce in situ data. We monitored fracture deformation at a cirque headwall in the Austria Alps. We found thermo-mechanical expansion and freeze-thaw action as dominant processes for deformation. Our results highlight the importance of liquid water in combination with subzero-temperatures on the destabilisation of glacier headwalls.
Processes destabilising recently deglaciated rocks, driving cirque headwall retreat, and putting...
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