Thermal properties of a supraglacial debris layer with respect to lithology and grain size

Abstract

This paper focuses on the impacts of debris cover on ice melt with regards to lithology and grain size. Ten test plots were established with different debris grain sizes and debris thicknesses consisting of different natural material. For each plot, values of thermal conductivity were determined. The observations revealed a clear dependence of the sub‐debris ice melt on the layer thickness, grain size, porosity and moisture content. For the sand fraction the moisture content played a dominant role. These test fields were water saturated most of the time, resulting in an increased thermal conductivity. Highly porous volcanic material protected the ice much more effectively from melting than similar layer thicknesses of the local mica schist. However, the analysis of thermal diffusivities demonstrated that the vertical moisture distribution of the debris cover must be taken into consideration, with the diffusivity values being significantly lower in deeper layers.

Key words:

• supraglacial debris
• ablation
• debris‐covered glaciers
• thermal conductivity
• thermal diffusivity
• Vernagtferner
• Austria

Acknowledgements

The authors would like to thank Ursula Blumthaler and Lina Seybold for assisting with the fieldwork. They also thank Maria Shahgedanova from the Walker Institute for Climate System Research, University of Reading, UK for providing two meteorological stations. The funding of the experiments by the Austrian Academy of Science, the Deutsche Forschungsgemeinschaft (MA 3347/4‐1) and the Bavarian Ministry of Environment is gratefully acknowledged.