Glacial hot spots for sediment supply during global warming: a case study from the Eastern Italian Alps

Glacial and proglacial zones of high-mountain regions are among the areas most affected by the ongoing climate warming. Rising temperatures accelerate glacial retreat and the degradation of permafrost, with a consequent increase of instability of steep rock walls, moraines, and slopes. This may increase sediment production that could either contribute to the debris cover of the retreating glaciers, or to an increase in the amount of sediment being transported through the proglacial zone and the more distant fluvial system. The contribution of a proglacial area to the total amount of sediment that exits a basin, however, depends on many factors and it is not yet clear, if sediment supply from such areas will continue to increase or decrease in future. Filling this knowledge-gap is crucial to be able to predict the transport capacity of glacial-fed fluvial systems, especially in relation to possible related hydrogeological hazards.

By analyzing aerial photographs and high-resolution digital surface models from a proglacial area in the Eastern Italian Alps, we demonstrate that these sources of sediment are intimately coupled with the position of the glacier through time; this also applies to the newly formed channel reaches that have evolved following glacial retreat. It follows that sediment sources can be “switched on” or “switched off” in relative short time periods, which are primarily influenced by climate-driven environmental change. Such a pulsed sediment production thus generates waves of sediment that may be entrained by the fluvial system depending on water availability and transport capacity. As such, a detailed and robust forecast of sediment yield for future scenarios may be possible if the spatial and environmental changes associated with glacier retreat and newly formed channel network are monitored and assessed.