A number of studies in our group have looked at debris-covered glaciers in recent years. What we have not really done yet is ask where the debris covering all that ice is actually coming from. In a new study, published recently in the Journal of Earth Surface Dynamics we are examining the contribution of sediment from the lateral moraines to the glacier surface.
Using repeat DEMs from multiple UAV flights between 2013 and 2018, we show that debris from the moraines can only reach the margins of the glacier surface but locally contributes to a considerable thickening of the cover.
The analysis shows that mass transport results in an elevation change on the lateral moraines with an average rate of +0.31m/year during this period, partly related to sub-moraine ice melt. There is a higher elevation change rate observed in the monsoon (+0.39 m/year) than in the dry season (+0.23 m/year).
The lower debris aprons of the lateral moraines decrease in elevation at a faster rate during both seasons, due to both the melt of ice below and mass wasting processes at the surface. The surface lowering rates of the upper gullied moraine, with no ice core below, translate into an annual increase in debris thickness of 0.08 m/year along a narrow margin of the glacier surface. Here the observed debris thickness is approximately 1 m, reducing melt rates of underlying glacier ice.
The paper and associated data is available open access here: https://www.earth-surf-dynam.net/7/411/2019/