Preprints
https://doi.org/10.5194/egusphere-2024-1600
https://doi.org/10.5194/egusphere-2024-1600
01 Jul 2024
 | 01 Jul 2024
Status: this preprint is open for discussion.

Creep enhancement and sliding in a temperate, hard-bedded alpine glacier

Juan-Pedro Roldán-Blasco, Adrien Gilbert, Luc Piard, Florent Gimbert, Christian Vincent, Olivier Gagliardini, Anuar Togaibekov, Andrea Walpersdorf, and Nathan Maier

Abstract. Glacier internal deformation is usually described by Glen's Law using two material parameters, the creep factor A and the flow law exponent n. However, the values of these parameters and their spatial and temporal variability are rather uncertain due to the difficulty of quantifying internal strain and stress fields at the natural scale. In this study, we combine 1-year long continuous measurements of borehole inclinometry and surface velocity with three-dimensional full Stokes ice flow modeling to infer ice rheology and sliding velocity in the ablation zone of the Argentière Glacier, a temperate glacier in the French Alps. We demonstrate that the observed deformation rate profile has limited sensitivity to the flow law exponent n and instead mainly reflects an increase in the creep factor A with depth, with A departing from its surface value by at least up to a factor of 2.5 below 160 m. We interpret this creep factor enhancement as an effect of increasing interstitial water content with depth from 0 % to 1.3 % which results in an average value of A = 148 MPa-3 a-1. We further observe that internal ice deformation exhibits seasonal variability similar to that in surface velocity, such that the local basal sliding velocity exhibits no significant seasonal variation. We suggest that these changes in deformation rate are due to variations in the stress field driven by contrasting changes in subglacial hydrology conditions between the side and the center of the glacier. Our study gives further evidence that borehole inclinometry combined with full-Stokes flow model allows constraining both ice rheology and basal friction at scales that cannot be inferred from surface velocity measurements alone.

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Juan-Pedro Roldán-Blasco, Adrien Gilbert, Luc Piard, Florent Gimbert, Christian Vincent, Olivier Gagliardini, Anuar Togaibekov, Andrea Walpersdorf, and Nathan Maier

Status: open (until 18 Aug 2024)

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  • RC1: 'Comment on egusphere-2024-1600', Dominik Gräff, 04 Jul 2024 reply
  • RC2: 'Comment on egusphere-2024-1600', Manuela Köpfli, 15 Jul 2024 reply
    • RC3: 'Reply on RC2', Manuela Köpfli, 15 Jul 2024 reply
Juan-Pedro Roldán-Blasco, Adrien Gilbert, Luc Piard, Florent Gimbert, Christian Vincent, Olivier Gagliardini, Anuar Togaibekov, Andrea Walpersdorf, and Nathan Maier
Juan-Pedro Roldán-Blasco, Adrien Gilbert, Luc Piard, Florent Gimbert, Christian Vincent, Olivier Gagliardini, Anuar Togaibekov, Andrea Walpersdorf, and Nathan Maier

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Short summary
The flow of glaciers and ice sheets is due to ice deformation and basal sliding driven by gravitational forces. Quantifying the rate at which ice deforms under its own weight is critical to assessing glacier evolution. This study uses borehole instrumentation in an Alpine glacier to quantify ice deformation and constrain its viscosity in a natural setting. Our results show that the viscosity of ice at 0° C is largely influenced by interstitial liquid water which enhances ice deformation.