Groundwater flow under a land-based palaeo-ice stream of the Scandinavian ice sheet and its geomorphological implications
|Location||International Geological Congress,oslo 2008|
|Author||Hermanowski, Piotr۱; Piotrowski, Jan A.۲; Piotrowski, Andrzej۳|
|Holding Date||07 October 2008|
Palaeo-ice streams of the southern part of the Scandinavian Ice Sheet substantially influenced ice balance, sediment transfer, and geomorphic processes in the central European Lowland. These ice streams terminated in large lobes projecting tens of km beyond the main ice sheet margin. They dramatically affected groundwater system by pressurizing it and recharging with glacial meltwater leading to re-organization of groundwater flow directions, velocities and fluxes in relation to non-glacial times. This profound modification of the subglacial groundwater drainage through a system of feedbacks affected the ice/bed coupling and the formation of subglacial landforms and sediments.
We have used experiments in time-dependent three-dimensional numerical modelling of subglacial groundwater flow to constrain interactions between ice, water and sediment under the Odra ice lobe, one of the main ice lobes of the southern part of the Scandinavian Ice Sheet during the last glaciation. The lobe covered an area of ca. 18,500 km2 in NE Germany and NW Poland protruding at least 45 km beyond the main ice marginal zone. Our Finite Difference (MODFLOW) model simulates groundwater flow in 35 time steps corresponding to different position of the advancing ice margin yielding temporal and spatial data. We focused on groundwater fluxes in the uppermost model layers to a depth of about 150 m.
The model shows evolution of groundwater fluxes, velocities and flow directions underneath the ice sheet and some distance in front of it during the advance. Coupling the simulation results with empirical estimates of basal melting rates suggests that, on the whole, only a small fraction of basal meltwater could have drained into the bed. The surplus water likely accumulated at the ice/bed interface facilitating fast ice flow as some combination of basal sliding and soft sediment deformation. On a local scale, the ice/bed interface appears as a mosaic of areas with groundwater discharge and recharge. Areas with noticeable groundwater upwelling from the bed to the glacier sole seem to spatially correspond with areas where eskers and drumlins occur. Tunnel valleys that post-date other subglacial landforms suggest that fast ice flow was terminated by rapid drainage of large amounts of water from the ice/bed interface through channels.