TC The Cryosphere TC The Cryosphere 1994-0424 Copernicus Publications Göttingen, Germany 10.5194/tc-7-877-2013 Density assumptions for converting geodetic glacier volume change to mass change Huss M. https://orcid.org/0000-0002-2377-6923 1 Department of Geosciences, University of Fribourg, 1700 Fribourg, Switzerland 27 05 2013 7 3 877 887 Copyright: © 2013 M. Huss 2013 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://tc.copernicus.org/articles/7/877/2013/tc-7-877-2013.html The full text article is available as a PDF file from https://tc.copernicus.org/articles/7/877/2013/tc-7-877-2013.pdf

The geodetic method is widely used for assessing changes in the mass balance of mountain glaciers. However, comparison of repeated digital elevation models only provides a glacier volume change that must be converted to a change in mass using a density assumption or model. This study investigates the use of a constant factor for the volume-to-mass conversion based on a firn compaction model applied to simplified glacier geometries with idealized climate forcing, and two glaciers with long-term mass balance series. It is shown that the "density" of geodetic volume change is not a constant factor and is systematically smaller than ice density in most cases. This is explained by the accretion/removal of low-density firn layers, and changes in the firn density profile with positive/negative mass balance. Assuming a value of 850 &pm; 60 kg m<sup>&minus;3</sup> to convert volume change to mass change is appropriate for a wide range of conditions. For short time intervals (&leq;3 yr), periods with limited volume change, and/or changing mass balance gradients, the conversion factor can however vary from 0–2000 kg m<sup>&minus;3</sup> and beyond, which requires caution when interpreting glacier mass changes based on geodetic surveys.

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