Breaking Britain: submerged and buried landforms suggest catastrophic flood breaching of the Dover Strait

The separation of Britain from mainland Europe in the late Quaternary is widely considered to be a consequence of spillover of a proglacial lake that occupied the present-day southern North Sea basin. This event had significant palaeogeographic, biological and archaeological implications. Lake spillover is inferred to have caused breaching of a Chalk rock dam to form the Dover Strait, thus releasing a significant flood into a subaerial English Channel. Whilst evidence for catastrophic flooding derived from sonar imaging of the seabed in the central Channel is strong, the breaching model is controversial through lack of data at the inferred spillpoint in the Dover Strait. We combine high-resolution sonar-derived bathymetry and seismic reflection data from the eastern English Channel to test the breaching hypothesis. We find a set of isolated, sediment-infilled depressions that are deeply incised into bedrock. Sub-circular to elliptical in planform, <4 kilometres in diameter and ~100 m in depth, these features are clustered along the projected trend of the Chalk dam and best interpreted as giant plunge pools formed by vertical drilling into bedrock by waterfalls. Bathymetric data show evidence of second opening event of the Strait. The floor of a prominent bedrock channel is eroded into cataracts and extensive longitudinal ridge-and-groove bedforms, features characteristic of erosion by catastrophic flood flows. This evidence strongly supports initial erosion of the Dover Strait by lake overspill, plunge pool erosion by waterfalls and subsequent dam breaching. Subsequent modification of the Strait by flood erosion of the Lobourg Channel may have been a consequence of spillover of younger ice-marginal lake systems.