1. Rock and Ice Physics Laboratory, Department of Earth Sciences, University College London, London WC1E 6BT, UK
2. Laboratoire de Glaciologie et Géophysique de l'Environnement, CNRS, St Martin d'Hères cedex, France
3. Department of Geosciences, Eberhard Karls University Tübingen, Wilhelmstrasse 56, Tübingen 72074, Germany
4. WSL Institute for Snow and Avalanche Research SLF, Davos 7260, Switzerland