EVALUATION OF MESO-SCALE TOPOGRAPHIC EFFECTS ON GLACIERS IN THE WESTERN HIMALAYA OF PAKISTAN

In the Topo-Ice Project for Pakistan that was funded by the U.S. Agency for International Development through the U.S. National Academy of Sciences, ~20 glaciers were examined in the Nanga Parbat and Karakoram Himalaya to assess the influence of topography on glacier fluctuations and geomorphological conditions. Specifically, we used ASTER imagery, Landsat ETM data, and an SRTM digital elevation model to examine supra-glacial conditions, fluctuation rates, and meso-scale topographic shielding influences that govern diffuse-skylight irradiance. Examination of Google Earth™ high-resolution imagery was also used to constrain the analysis. Our results depict spatial patterns associated with relief variations and glacier debris cover, in addition to recognition of relief variations in the accumulation zone related to the potential magnitude of snow avalanches. In addition, patterns of topographic shielding are highly variable, and assuming that diffuse-skylight irradiance is isotropic, some glaciers collectively receive different magnitudes of this irradiance component. Furthermore, altitudinal variation in topographic shielding varies for many glaciers, as some exhibit a pattern of decreasing shielding with altitude, while other exhibit increasing shielding with altitude. These patterns reflect varied historical conditions related to climate, tectonics and surface processes, as they govern erosion and relief production. Collectively, our results explain the highly varied nature of glacier fluctuations in the western Himalaya, as topography influences debris-cover variation, surface irradiance and melt-water production. These results demonstrate the importance of carefully interpreting glacier responses to climate change, as multi-scale topographic factors govern the relatively high spatial variability in glacier fluctuations, and regional extrapolation based upon results from one glacier would be problematic. More research is required to better ascertain the nature of the spatio-temporal variations in topographic effects.