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The Cryosphere An interactive open-access journal of the European Geosciences Union
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Preprints
https://doi.org/10.5194/tc-2020-133
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/tc-2020-133
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  05 Jun 2020

05 Jun 2020

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This preprint is currently under review for the journal TC.

Crystallographic analysis of temperate ice on Rhonegletscher, Swiss Alps

Sebastian Hellmann1,2, Johanna Kerch3, Ilka Weikusat3,4, Andreas Bauder1, Melchior Grab1,2, Guillaume Jouvet5,6, Margit Schwikowski4, and Hansruedi Maurer2 Sebastian Hellmann et al.
  • 1Laboratory of Hydraulics, Hydrology and Glaciology (VAW), ETH Zurich, Zurich, Switzerland
  • 2Institute of Geophysics, ETH Zurich, Zurich, Switzerland
  • 3Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
  • 4Department of Geosciences, Eberhard Karls University, Tübingen, Germany
  • 5University of Zürich, Department of Geography, Switzerland
  • 6ETH Zürich, Autonomous Systems Laboratory, Switzerland

Abstract. The crystal orientation fabric (COF) was studied at an ice core that was obtained from the temperate Rhonegletscher, located in the Central Swiss Alps. Seven samples, extracted at depths between 2 and 79 m, were analysed with an automatic fabric analyser. The COF analysis revealed conspicuous four-maxima patterns of the c-axis orientations at all depths. Additional data, such as microstructural images, produced during the ice sample preparation process, were considered to interpret these patterns. Furthermore, repeated high-precision Global Navigation Satellite System (GNSS) surveying allowed the local glacier flow direction to be determined. The relative movements of the individual surveying points indicated horizontal compressive stresses parallel to the glacier flow. Finally, numerical modelling of the ice flow permitted to estimate the local stress distribution. An integrated analysis of all the data sets provided an explanation for the observed four-maximum patterns in the COF. The average azimuths and colatitudes of the c-axes of the individual core samples align with the compressive stress directions obtained from numerical modelling. The clustering of the c-axes in four maxima surrounding the predominant compressive stress direction is most likely the result of a fast migration recrystallisation in combination with the presence of significant shear stresses. This interpretation is supported by air bubble analysis of the LASM images. Our results indicate that COF studies, which were so far predominantly performed at cold ice samples from the polar regions, can also provide valuable insights on the stress and strain distribution within temperate glaciers.

Sebastian Hellmann et al.

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Sebastian Hellmann et al.

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Latest update: 17 Sep 2020
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Short summary
In this study, we analyse the orientation of ice crystals in an Alpine glacier and compare this orientation with the ice flow direction. We found that the crystals orient in the direction of the largest stress which is in flow direction in the upper parts of the glacier and in vertical direction for deeper zones of the glacier. The grains cluster around this maximum stress direction in particular four-point maxima most likely as a result of recrystallisation under relatively warm conditions.
In this study, we analyse the orientation of ice crystals in an Alpine glacier and compare this...
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