Flow dynamics, sedimentation and erosion of glacial lake outburst floods along the Middle Pleistocene Scandinavian Ice Sheet (northern central Europe)

Abstract

During the Middle Pleistocene late Saalian glaciation of northern central Europe numerous pro‐glacial lakes formed along the southwestern margin of the Scandinavian Ice Sheet. Little is known about the drainage history of these lakes, the pathways of glacial lake outburst floods and their impacts on erosion, sedimentation and landscape evolution. This study investigated the impact of the late Saalian Weser and Münsterland Lake (Germany) outburst floods. In particular, we reconstructed the routing and flow dynamics of the lake outburst flood and analysed the flood related sediments. We employed one‐dimensional hydraulic modelling to calculate glacial lake outburst flood hydrographs. We modelled the flow pathway and local flow conditions along the pathway based on the boundary conditions of two different hydrographs and two different ice‐margin positions. The modelling results were compared with geomorphological and sedimentological field data in order to estimate the magnitude and impact of the flood on erosion and sedimentation. Two major lake drainage events are reconstructed for the study area, during which approximately 90–50 km3 of water was released. Modelling results indicate that the lake outburst floods created a high‐energy flood wave with a height of 35–50 m in confined valley areas that rapidly spread out into the Lower Rhine Embayment eventually flowing into the North Sea basin. The sedimentary record of the outburst floods comprises poorly sorted coarse‐grained gravel bars, long‐wavelength bedforms and sandy bedforms deposited by supercritical and subcritical flows. Some parts of the sandy flood deposits are rich in reworked mammoth bones or mammoth and horse teeth, pointing to reworking of older fluvial sediments, hydraulic concentration and subsequent re‐sedimentation of vertebrate remains. These deposits are preserved in sheltered areas or at high elevations, well above the influence of postglacial fluvial erosion. The flood‐related erosional features include up to 80‐m‐deep scour pools, alluvial channels and streamlined hills.

Ice‐marginal forced regressive deltas in glacial lake basins: geomorphology, facies variability and large‐scale depositional architecture

“…The geological setting and type of dam exert key controls on proglacial lake growth and drainage. Forced regression characteristically occurs during deglaciation when lake outlets are opened and rapid lake-level falls may occur (Kehew & Teller 1994;Ashley 1995;Brookfield & Martini 1999;Winsemann et al 2011;Carrivick & Tweed 2013;Winsemann et al 2016). In contrast to glaciomarine settings, glacial lake basins are typically characterized by an initial baselevel rise during glacier advance, as the glacier blocks drainage outlets.…”

“…The blocking of river valleys by the Middle Pleistocene Elsterian and Saalian ice sheets led to the repetitive formation of proglacial lakes (Eissmann 2002;Winsemann et al 2007Winsemann et al , 2009Roskosch et al 2015;Lang et al 2018). During deglaciation, the lakes catastrophically drained due to the renewed opening of lake outlets, which caused rapid, high-magnitude lake-level falls in the range of 20-80 m within perhaps a few weeks (Meinsen et al 2011;Winsemann et al 2011Winsemann et al , 2016Lang et al 2018). Maximum lake levels of~200 m a.s.l.…”

“…In contrast to glaciomarine settings, glacial lake basins are typically characterized by an initial baselevel rise during glacier advance, as the glacier blocks drainage outlets. Forced regression characteristically occurs during deglaciation when lake outlets are opened and rapid lake-level falls may occur (Kehew & Teller 1994;Ashley 1995;Brookfield & Martini 1999;Winsemann et al 2011;Carrivick & Tweed 2013;Winsemann et al 2016).…”

Paleohydraulic Reconstruction of Modern Large Floods at Subcritical Speed in a Confined Valley: Proof of Concept

“…Commonly, sedimentary sequences have been used in paleohydrology to reconstruct megafloods e.g., [1,[5][6][7][8]10,24], historical floods [20,27] and glacial-lake outburst floods [2][3][4]25]. This study has shown that instrumental records and PSI-HWMs can be used together to check the accuracy of the 2D paleohydraulic reconstruction of recent floods in a well-gauged river.…”

“…Two-dimensional hydraulic modelling has become a standard in paleohydrology [2,3,7,[23][24][25]] similar to slope-conveyance, slope-area methods and step-backwater analysis [11,26,27]-perhaps due to recent advances in computational power, the availability of Digital Elevation Models (DEM) and open-source 2D codes, e.g., DassFlow-Shallow [28,29]. Guidelines in the development and application of computational methods to environmental fluid mechanics, including quantification of uncertainty and model testing, can be found in [30].…”