Lead


Lay summary
Abstract:Rhonegletscher started to retreat behind a rock riegel and a proglacial lake started to form. The project plans to investigate the calving mechanims and the influence of the topography of the lake bed on the retreat of the glacier. Background: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. Calving into proglacial lakes may enhance mass loss and accelerate the retreat, and thus introduces a non-climatic process into the dynamics of a calving glacier. The retreat into deeper 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 colder climate is necessary to enable the glacer to return to the former position. Rhonegletscher, Swiss Alps, has retreated behind a rock riegel and a proglacial lake started to form for the first time in summer 2005. The terminus is expected to retreat fast into the deeper part of the basal topographic depression and will provide an easily accessible example to investigate calving. Goal:The goal of the project is to gain a more thorough understanding of the dynamics of lake-terminating glaciers in a changing climate and to understand the impact of basal sliding, stress evolution and thermal erosion and lake water temperature at the terminus on the calving rate, and to develop a new physics based mathematical model to predict the retreat rate of the glacier terminus.Significance:Proglacial and periglacial lakes are frequently formed in times of warming climate and retreating glaciers. Depending on the nature of the dam, such lakes may drain catastrophically and thus form a one-time or repeated threat to the valleys downstream of the lakes. Calving may accelerate the retreat of glaciers. In the case of a basal depression near the glacier terminus, this may lead to different steady states for given climatic conditions. This introduces a non-climatic signal in the dynamics of glaciers, which may be significant for the reconstruction of past glacierisations and for the future advance or retreat of glaciers.