Project

glacier; proglacial lakes; calving; basal sliding; numerical model; damage mechanics; glacier retreat; modelling

Lead
Lay summary
In a warming climate with many glaciers retreating, proglacial lakes may form if either a moraine dams the water or the terminus retreats across a basal depression. In the Alps, the number of such lakes is expected to increase in the closer future. This introduces an ablation mechanism which formerly was of very little significance on alpine glaciers: Calving into proglacial lakes may enhance mass loss and considerably accelerate glacial retreat.The mechanism finally causing icebergs to break off is not fully understood yet. Calving is strongly related to basal sliding, which in turn is related to the subglacial hydraulics. A better understanding of these process-interactions to better constrain the numerical models is required to enable better prediction of the response of glaciers to climatic warming.Rhonegletscher, Swiss Alps, has recently retreated behind a rock riegel; a proglacial lake started to form for the first time in 2005. In the future an accelerated retreat through a basal depression involving the formation of a calving front is expected. The tongue of Rhonegletscher therefore offers a unique opportunity to study the retreat of an Alpine lake-terminating glacier, the involved fracturing processes and the calving mechanism. Theoretical and modeling research will be combined with field measurements on Rhonegletscher, in order to constrain and validate the obtained models.

Direct link to Lay Summary

Last update: 21.02.2013

Active participation

Communication	Title	Media	Place	Year

Number	Title	Start	Funding scheme

In a warming climate with many glaciers retreating, proglacial lakes may form if either a moraine dams the water or the terminus retreats across a basal depression. In the Alps, the number of such lakes is expected to increase considerably in the closer future, thus, knowledge of the calving processes in lacustrine environments more and more gains in importance for the prediction of Alpine glacier retreat.This introduces an ablation mechanism which formerly was of very little importance on Alpine glaciers: Calving into proglacial lakes may enhance mass loss and considerably accelerate glacial retreat. The retreat into deeper water and the advance into shallower water seems to be unstable. Thus, crossing of a depression leads to a lag in the cycle: once a glacier retreated behind the deepest part of a depression, a much more positive mass balance is necessary to enable the glacier to return to the former position.Calving seems to be strongly related to basal sliding, which in turn is related to the subglacial hydraulics. Both calving and sliding involve discontinuous processes. Calving is difficult to observe because the calving terminus is a dangerous environment, and sliding processes at the glacier bed are difficult to access. However, an improved understanding of the aforementioned processes to better constrain the numerical models is required for an accurate prediction of the response of calving glaciers to climatic warming.Several phenomenological relations have been formulated to predict calving rates; the most successful ones relates the calving to fracturing processes due to the stress conditions close to the calving front. Therefore it seems that further research on glacier calving should focus on the understanding of the fracturing mechanisms appearing in this context.Rhonegletscher, Swiss Alps, has recently retreated behind a rock riegel; a proglacial lake started to form for the first time in 2005. In 2009, the lake has been growing further, and interesting fracturing processes such as the formation of a shear zone have appeared. In the future an accelerated retreat through a basal depression involving the formation of a calving front is expected. The tongue of Rhonegletscher therefore offers a unique opportunity to study the retreat of an Alpine lake-terminating glacier, the involved fracturing processes and the calving mechanism. In our study, field observations of ice deformation and englacial hydraulics are combined with most recent numerical modeling techniques, in order to obtain a more profound knowledge of the calving mechanisms in lacustrine environments and to make more reliable predictions of the retreat of Alpine glaciers ending in lakes possible.