Quantification of glacier volume change using topographic and ASTER DEMs

Satellite imagery has been largely used to measure glacier surface evolution by detecting surface change between two images taken at different dates. But until now it seemed difficult to evaluate glacier volume changes from space. In this study, volume changes of three small glaciers in the Cordillera Blanca (northern Peru) between 1962 and 2001 are observed using differences between two Digital Elevation Models (DEMs). The first DEM was created from topographic measurements and aerial photographs made by the National Institute of Geography (IGN) of Peru in 1962, and the second was created from ASTER stereo images acquired in 2001. The IGN DEM has an approximate error of +/- 10 m whereas the Aster DEM has an rms error of +/$22 m with individual errors of up to 58 m. By comparing the two DEMs, appreciable altitude differences between them could be seen. On glacier-covered areas, these altitude differences correspond to volume losses, due to ablation on the lower parts of the glaciers. On a small valley glacier with an ablation area of /spl sim/2.25 km/sup 2/ we were able to quantify a volume loss of /spl sim/47.10/sup 6/ m/sup 3/ water equivalent in 39 years. These results, although they are affected by relatively big errors due to the small size of the glaciers and the mountainous topography which induces errors in the DEMs construction, confirms a tendency of glacier melting, justifying concerns about the water supply in the valley during the dry season in the next few decades.