Britain’s geological separation from mainland Europe may have been a two-stage process according to a study in Nature Communications this week. New evidence indicates that the opening of the Dover Strait - the narrowest gap between Britain and Europe - was the result of erosion caused by an overflowing glacial lake followed by catastrophic flooding. Determining how the Strait was breached has implications for our understanding of how the creation of island Britain altered colonisation of the British Isles and changed the drainage of water from northwest Europe.
Britain was once connected to continental Europe via a chalk ridge that extended from southeast England to northwest France. Previous theories have suggested that spillover from a glacial lake contributed to the opening of the Dover Strait, but testing this hypothesis has been limited by a lack of high-resolution data from the inferred breach-point.
Sanjeev Gupta and colleagues present new evidence that suggests the opening of the Strait involved at least two major episodes of erosion. Their analyses support a model of lake overspill causing initial erosion around 450,000 years ago, in which waterfalls cut through the chalk and caused a rock dam to fail, releasing lake water into the English Channel. The data reveals that a second catastrophic flooding event was needed to fully open the Dover Strait; the timing of this event is not clear, but it was likely around 160,000 years ago, the authors suggest, based on marine mollusc assemblages in coastal sediments.