Flooding Northern Germany: Impacts and Magnitudes of Middle Pleistocene Glacial Lake-Outburst Floods

The major objective of this study is to summarise the routing and impact of lake- outburst floodsalong the south-western margin of the Middle Pleistocene (Saalian) Fennoscandian ice sheet. We provide an overview about the spatial and temporal evolution and drainage history of ice-dammedlakes in northern Germany. The repeated drainage of these ice-dammedlakes contributed to the destabilisationof the ice margin and triggered ice-streamingand/or local re-advances. Major flood-related channels became part of the ice-marginal drainage system during the decay of the Saalian ice sheets. The most proximal lake- outburst flooddrainage routes are characterised by deep plunge pools, channels, megaflutes, scour pools and streamlined hills cut into Pleistocene deposits and Cenozoic and Mesozoic bedrock. Depositional features include large sand and gravel bars and fields of sandy bedformsdeposited by supercritical to subcritical flows. The clast composition of bars commonly indicates a strong reworking and redeposition of local fluvial and colluvial material, partly rich in mammothbones. To quantify flow characteristics during glacial lake-outburst floods, 2D hydraulic simulations were conducted for different ice-margin configurations and flood hydrographs. Subsequently, the model outcomes were compared with the sedimentological and geomorphological evidence for the lake-drainage events in order to estimate the most likely flood pathways, the impact of the flood on erosion, sediment distribution and post-glacial landscape evolution.