Debris-covered glaciers encourage subglacial sediment accumulation and limit erosion

Glaciers are well known for their erosive power and the large quantities of sediment that they expel. Glacier sliding sculpts the landscape and creates sediment, while englacial debris advection and subglacial sediment transport can expel this material from the glacier terminus. In alpine regions, rockfall from mountain slopes adds debris to the glacier surface, which can be buried and advected down-valley as the glacier moves. When the debris melts out to the surface, it limits surface melt and changes the glacier’s surface slope. The reduced melt and change to the glacier surface slope impact the sediment transport capacity below the glacier.

We couple numerical models of debris-covered glacier dynamics and subglacial sediment transport to show that debris-covered glaciers are expected to erode at a slower rate than clean glaciers. The model outputs also demonstrate that sediment eroded below glaciers can accumulate below debris-covered portions due to limited sediment transport capacity. Reduced melt and surface slope limit the sediment transport capacity, resulting in sediment deposition. This sediment deposition creates till layers that may alter glacier dynamics. Additionally, the results demonstrate that debris cover can change the connectivity of sediment below glaciers and store glacially eroded sediment subglacially. These findings demonstrate the complicated interactions amongst glacier dynamics, hydrology, erosion, and sediment transport. The processes identified here have substantial implications for the transport of sediment in rapidly changing mountain landscapes experiencing glacier retreat and changing hydrology.