Catastrophic flooding origin of shelf valley systems in the English Channel

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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 France2,3,4. This hypothesis has remained untested through lack of direct evidence, and alternative non-catastrophist ideas have been entertained for valley formation5,6. 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.

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Figure 1: Location map and inferred distribution of palaeovalleys on the English Channel shelf.
Figure 2: Sonar bathymetry of the north-central English Channel shelf.
Figure 3: Details of geomorphology of the Northern Palaeovalley.
Figure 4: Bathymetry images showing tributary confluence morphology and post-flooding secondary drainages.

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Acknowledgements

The bathymetry surveys were funded by the Maritime and Coastguard Agency under the UK Civil Hydrography Programme; we thank J. Collins and R. Spillard for support. Data acquisition for Fig. 4b was funded by the Aggregates Levy Sustainability Fund through English Heritage and by the Joint Research Equipment Initiative (HEFCE/HEFCW). We thank B. Coakley, A. Densmore, R. S. Anderson, P. A. Allen, C. Paola, S. Parfitt, R. Preece and N. Ashton for discussions, and V. Baker and P. Gibbard for their comments.

Author Contributions S.G. and J.S.C. analysed the bathymetry data and wrote the paper. G.P. compiled and processed the data, together with A.P.-F. who also aided the analysis.

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Correspondence to Sanjeev Gupta.

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Supplementary information

Supplementary Information

This file contains Supplementary Notes with additional discussion of interpretation of flood landforms and Supplementary Figures S1-S3. Supplementary Figure S1 shows high-resolution details of the margin of the Northern Palaeovalley; Supplementary Figure S2 shows the location of detailed bathymetry images in Figures 3 and 4; Supplementary Figure S3 shows a LANDSAT satellite image of some streamlined islands in the Channelled Scabland. (PDF 3798 kb)

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Gupta, S., Collier, J., Palmer-Felgate, A. et al. Catastrophic flooding origin of shelf valley systems in the English Channel. Nature 448, 342–345 (2007) doi:10.1038/nature06018

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