Flooding Northern Germany: Impacts and Magnitudes of Middle Pleistocene Glacial Lake-Outburst Floods
2020
The major objective of this study is to summarise the routing and impact of lake-outburst floods along 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-dammed lakes in northern Germany. The repeated drainage of these ice-dammed lakes contributed to the destabilisation of the ice margin and triggered ice-streaming and/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 flood drainage 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 bedforms deposited 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 mammoth bones. 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.
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