Elevation change measurements provide information on the gain or loss in glacier elevation and volume. It is usually computed by differencing of digital terrain models from different points in time. These digital terrain models typically result from aerial geodetic surveys (e.g. from photogrammetry or laser-scanning) that are repeated at multi-annual or decadal intervals. The results are reported as (annual) average elevation change (rate) in the unit meter or millimeter (per year) with positive or negative values indicating a glacier elevation gain or loss, respectively. The average elevation changes multiplied by the glacier surface area corresponds to glacier volume change. The annual rates of glacier elevation change can – after a density conversion – be compared to glacier mass balance.
A glacier with sustained negative/ positive elevation change will – with a certain delay – start to retreat/advance until its extent reaches again equilibrium with climatic conditions.

Figure 1. Map showing elevation changes at Findelengletscher and Adlergletscher, Switzerland, between 2005 and 2010. Data used are airborne laser scanning digital elevation models (DEMs) at a one meter raster resolution. The non-colored background represents the hillshaded DEM from 2005. The average elevation change is -3.18 m for Findelengletscher and -1.76 m for Adler-gletscher. Maximum ice losses at the tongue are measured up to -35 m, whereas only few areas with an increased elevation are present in the accumulation area. Source: Joerg et al., 2012..

Figure 2. Average thickness changes per year (effective changes are shown in dark red, in light red erroneous thickness changes and positive ones in blue) with applied stochastic uncertainties. Source: Rastner et al,.2016.

References

Joerg, PC Morsdorf, F. und Zemp, M. (2012): Topografische Veränderungen des Findelengletschers, Wallis, Schweiz, 2005-2010. Karte 1:15’000. In: WGMS (2012): Fluctuations of Glaciers 2005-2010 (Vol. X): Zemp, M., Frey, H., Gärtner-Roer, I., Nussbaumer, SU, Hoelzle, M., Paul, F. und Haeberli, W. (Hrsg.), ICSU (WDS) / IUGG (IACS) / UNEP / UNESCO / WMO, World Glacier Monitoring Service, Zürich, Schweiz: 336p.

Rastner, P., Joerg, PC, Huss, M. und Zemp, M. (2016): Historische Analyse und Visualisierung des Rückzugs des Findelengletschers, Schweiz, 1859–2010. Global and Planetary Change, 145: S. 67-77. http://dx.doi.org/10.1016/j.gloplacha.2016.07.005