Arbeitsbericht NAB 10-18

Glaciological conditions in northern Switzerland during recent Ice Ages

Based primarily on reconstructions and various model calculations, quantitative estimates are compiled concerning ice conditions in northern Switzerland during the past Ice Age. The penetration of winter sea ice to low latitudes and the corresponding closure of the Atlantic Ocean as a humidity source caused extremely cold/dry conditions in central Europe during the time period of maximum cold and most extended area of surface ice. At this stage, the large lobes of the piedmont glaciers spreading out over much of the Swiss Plateau were predominantly polythermal to cold, surrounded by continuous periglacial permafrost up to 150 m thick and characterised by low driving stresses (typically 30 to 50 kPa). Mass balance gradients, mass turnover and ice flow velocities on these piedmont glaciers were correspondingly low. Subsurface temperatures and groundwater conditions were strongly influenced by the presence of extended surface and subsurface ice. Glacial erosion in the ice-marginal zones was probably limited due to strongly reduced basal sliding and melt-water flow. More humid conditions with higher flow velocities, more basal sliding and stronger erosion by abrasion and melt-water effects must have prevailed during ice advance across the Swiss Plateau, and rapid downwasting or even collapse (calving instability in lakes) is likely to have taken place during the retreat phase back into the Alpine valleys. It appears plausible to assume that similar cycles were characteristic for past Ice Ages in general and could also be characteristic for future Ice Age conditions in northern Switzerland. Some key questions concerning effects of deep glacial erosion are formulated.