Comparison of Late Pleistocene and Modern Glacier Extents in Central Nepal Based on Digital Elevation Data and Satellite Imagery

Late Pleistocene and modern ice extents in central Nepal are compared to estimate equilibrium line altitude (ELA) depressions. New techniques are used for determining the former extent of glaciers based on quantitative, objective geomorphic analyses of a 90-m resolution digital elevation model (DEM). For every link of the drainage network, valley form is classified as glacial or fluvial based on cross-valley shape and slope statistics. Down-valley transitions from glacial to fluvial form indicate the former limits of glaciation in each valley. Landsat Multispectral Scanner imagery for the same region is used to map current glacier extents. For both full-glacial and modern cases, ELAs are computed from the glacier limits using the DEM and a toe-to-headwall altitude ratio of 0.5. Computed ELA depressions range from 100–900 m with a modal value of 650 m and a mean of 500 m, values consistent with previously published estimates for the central Himalaya but markedly smaller than estimates for many other regions. We suggest that this reflects reduced precipitation, rather than a small temperature depression, consistent with other evidence for a weaker monsoon under full-glacial conditions.