1. Department of Earth Science and Engineering, Imperial College London, London SW7 2AZ, UK
2. UK Hydrographic Office, Admiralty Way, Taunton, Somerset TA1 2DN, UK

Correspondence to: Sanjeev Gupta¹ Correspondence and requests for materials should be addressed to S.G. (Email: s.gupta@imperial.ac.uk).

Abstract

Megaflood events involving sudden discharges of exceptionally large volumes of water are rare, but can significantly affect landscape evolution, continental-scale drainage patterns and climate change¹. It has been proposed that a significant flood event eroded a network of large ancient valleys on the floor of the English Channel—the narrow seaway between England and France^{2, 3, 4}. This hypothesis has remained untested through lack of direct evidence, and alternative non-catastrophist ideas have been entertained for valley formation^{5, 6}. Here we analyse a new regional bathymetric map of part of the English Channel derived from high-resolution sonar data, which shows the morphology of the valley in unprecedented detail. We observe a large bedrock-floored valley that contains a distinct assemblage of landforms, including streamlined islands and longitudinal erosional grooves, which are indicative of large-scale subaerial erosion by high-magnitude water discharges. Our observations support the megaflood model, in which breaching of a rock dam at the Dover Strait instigated catastrophic drainage of a large pro-glacial lake in the southern North Sea basin². We suggest that megaflooding provides an explanation for the permanent isolation of Britain from mainland Europe during interglacial high-sea-level stands⁷, and consequently for patterns of early human colonisation of Britain together with the large-scale reorganization of palaeodrainage in northwest Europe⁴.

1. Department of Earth Science and Engineering, Imperial College London, London SW7 2AZ, UK
2. UK Hydrographic Office, Admiralty Way, Taunton, Somerset TA1 2DN, UK

Correspondence to: Sanjeev Gupta¹ Correspondence and requests for materials should be addressed to S.G. (Email: s.gupta@imperial.ac.uk).

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