Glaciology and Geomorphology, Part of PROSA

In the framework of the DFG package "High resolution measurements of geo-morpho-dynamics in fast changing proglacial systems (PROSA)" the present subproject "Glaciology and geomorphology" investigates mass exchange on and below, and ice flow in glacier tongues, their implication for melt water production, erosion and sediment transport, all three of which are coupled by feedbacks, under the conditions of recent rapid changes in the alpine cryosphere. As a novelty we attempt to separate surface and basal melting by measuring surface ablation by standard glaciological methods and total volume change by laser scans. Basic understanding of the processes involved will be enhanced by high spatial and temporal resolution. Another novelty is the vibroseismic detection of the thickness of both ice and underlying sediments at a temperate glacier tongue.

Glaciers have sculptured the surface of the Alps for hundreds of thousands of years. The U-shaped alpine valleys have been eroded by the ice that flowed down from the highest peaks to the forelands north and south of the mountains. We owe the existence of Lake Garda, Lake Constance or Lake Geneva to this ice age erosion. On a smaller time scale since about 1600 AD, climate fluctuations have prompted alpine glaciers to advance on a local scale, usually not going below 2000 m asl. In these advances they left their marks when they deposited the material they had eroded at their base as terminal or lateral moraines. Since their maximum stage 1850 AD they have been melting at an accelerating pace, interrupted by only minor re-advances around 1920 and 1980. This retreat promoted a different kind of erosion: that of till and sediments by water below the glaciers and by landslides from the lateral moraines. They used to be covered and supported by the glacier and are now being transported down valley in form of suspensions and bed load of the rivers, reshaping the landscape and gradually filling the basins of alpine power plants. This mass transport is the central theme of the multi-facetted PROSA Project. The subproject Glaciology observes and measures on top, in, and below the moving and melting ice. Cavities are being melted out by water at the base of the glaciers; they implode and cause funnel shaped depressions of the ice surface. Their development and the motions of rocks lying on the glacier surface which indicate the speed of ice flow are being monitored by two automated cameras on either side of the glacier tongue. Three daily pictures help to quantify these processes. The change of the glacier tongue is recorded at the beginning and at the end of the winter season by airborne laser scanning at an accuracy of few centimeters in order to measure motion and mass balance of the glacier tongue. Its thickness is determined by ice penetrating radar. Its internal layering and changes in the subglacial sediments are annually recorded by vibroseismic soundings, the most recent development in the sensing of ice and subglacial structure. Other subprojects of PROSA monitor mass transport in the melt water and erosion of lateral moraines and sediments in front of the glacier, altogether providing a modern view of processes and changes in the glacier environment in the course of recent climate change.