GLACIATIONS, PERMAFROST, AND PALEO GROUNDWATER FLOW IN SWITZERLAND

We developed a hydrogeologic model using Elmer/Ice to study the impacts of permafrost development and glaciations on regional groundwater flow patterns across Switzerland over the past 100,000 years. Elmer/Ice is a high-performance computer code that solves for coupled variable-density groundwater flow, heat transfer (including permafrost formation/melting), and geomechanical loading. Permeability reduction in the model occurs as a function of pore fluid ice content. The model included 12 hydrostratigraphic units as well as a thick portion of the underlying crystalline basement. The cross-sectional model was oriented NW-SE from the Alps into the foreland region of Switzerland and was 132 km in length and over 15 km thick. We used sine function boundary conditions to represent temporal changes in ice sheet thickness and land surface temperatures along the top boundary. Model results indicate that following the glacial maximum, permafrost formation occurred within the Alps which partially blocked upland recharge. At the glacial maximum, the thick alpine ice sheet maintains wet-based conditions enhancing recharge. Enhanced hydraulic gradients during periods of glaciation resulted in temperature overturns due to convective heat transfer effects both in upland and lowland regions. The overturns in the lowland profiles are not observed in lowland today due to lower groundwater flow rates and vertical conductive thermal relaxation. The model results should be viewed as conceptual since we imposed idealized boundary conditions.