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Discussion papers | Copyright
https://doi.org/10.5194/tc-2018-83
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 06 Jun 2018

Research article | 06 Jun 2018

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

Supraglacial debris thickness variability: Impact on ablation and relation to terrain properties

Lindsey I. Nicholson1, Michael McCarthy2,3, Hamish Pritchard2, and Ian Willis3 Lindsey I. Nicholson et al.
  • 1Department of Atmospheric and Cryospheric Sciences, Universiät Innsbruck, Innsbruck, Austria
  • 2British Antarctic Survey, United Kingdom Research and Innovation, Madingley Road, Cambridge, UK
  • 3Scott Polar Research Institute, University of Cambridge, Cambridge, UK

Abstract. Shallow ground penetrating radar (GPR) surveys are used to characterize the small-scale spatial variability of supraglacial debris thickness on a Himalayan glacier. Debris thickness varies widely over short spatial scales. Comparison across sites and glaciers suggests that the skewness and kurtosis of the debris thickness frequency distribution decrease with increasing mean debris thickness, and we hypothesise that this is related to the degree of gravitational reworking the debris cover has undergone, and is therefore a proxy for the maturity of surface debris covers. In the cases tested here, using a single mean debris thickness value instead of accounting for the observed small-scale debris thickness variability underestimates modelled midsummer sub-debris ablation rates by 11–30%. While no simple relationship is found between measured debris thickness and morphometric terrain parameters, analysis of the GPR data in conjunction with high-resolution terrain models provides some insight to the processes of debris gravitational reworking. Periodic sliding failure of the debris, rather than progressive mass diffusion, appears to be the main process redistributing supraglacial debris. The incidence of sliding is controlled by slope, aspect, upstream catchment area and debris thickness via their impacts on predisposition to slope failure and meltwater availability at the debris-ice interface. Slope stability modelling suggests that the percentage of the debris-covered glacier surface area subject to debris instability can be considerable at glacier scale, indicating that up to 22% of the debris covered area is susceptible to developing ablation hotspots associated with patches of thinner debris.

Lindsey I. Nicholson et al.
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Lindsey I. Nicholson et al.
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Short summary
Ground penetrating radar of supraglacial debris thickness is used to study local thickness variability. Freshly emergent debris cover appears to have higher skewness and kurtosis than more mature debris covers. Accounting for debris thickness variability in ablation models can result in markedly different ice ablation than is calculated using the mean debris thickness. Slope stability modelling reveals likely locations for locally thin debris with high ablation.
Ground penetrating radar of supraglacial debris thickness is used to study local thickness...
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