Estimate of ablation rate of glacier ice under a supraglacial debris layer

The ablation rare under a debris layer is very difficult to measure directl y at debris-covered glaciers, because the surface is highly heterogeneous, and the ablation rate varies tremendously from place to place. Heat budget considerations with a debris layer on top of glacier ice suggested that 'th ermal resistance' of me debris layer could be estimated from surface temper ature and the heat fluxes at the debris surface, and the ablation rate of d ie underlying glacier ice from the thermal resistance and meteorological da ta. The method was tested at the Lirung Glacier in Langtang Valley, Nepal H imalayas, using the thermal band of LANDSAT satellite for estimating surfac e temperature distribution of the debris top surface. The amount of melt wa ter thus estimated was compatible with the observed discharge data from the glacier basin for periods of the monsoon season in 1985 and the pre-monsoo n to the monsoon season in 1996. The investigation also revealed that the a mount of discharge was much larger than the amount of precipitation over th e basin, and it was suggested that the melt water from the debris-covered g lacier contributes significantly to the river flow as a result of the shrin kage of the glacier.