Glacier fluctuations between 1975 and 2008 in the Greater Himalaya Range of Zanskar, southern Ladakh

Glaciers in the Himalaya are often heavily covered with supraglacial debris, making them difficult to study with remotely-sensed imagery alone. Various methods such as band ratios can be used effectively to map clean-ice glaciers; however, a thicker layer of debris often makes it impossible to distinguish between supraglacial debris and the surrounding terrain. Previously, a morphometric mapping approach employing an ASTER-derived digital elevation model has been used to map glaciers in the Khumbu Himal and the Tien Shan. This study on glaciers in the Greater Himalaya Range in Zanskar, southern Ladakh, aims (i) to use the morphometric approach to map large debris-covered glaciers; and (ii) to use Landsat and ASTER data and GPS and field measurements to document glacier change over the past four decades. Field work was carried out in the summers of 2008. For clean ice, band ratios from the ASTER dataset were used to distinguish glacial features. For debris-covered glaciers, topographic features such as slope were combined with thermal imagery and supervised classifiers to map glacial margins. The method is promising for large glaciers, although problems occurred in the distal and lateral parts and in the fore field of the glaciers. A multitemporal analysis of glaciers in Zanskar showed that in general they have receded since at least the mid- to late-1970s. However, some few glaciers that advanced or oscillated — probably because of specific local environmental conditions — do exist.