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The real story behind Britain’s geological exit
New evidence from the floor of the Dover Strait helps paint a picture of how the island has repeatedly separated from and rejoined the European continent.
Philip Gibbard 7 Jun 2017 in Research & Technology
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| The lake that spilled over to separate Great Britain from Europe Credit: Imperial College London |
More than 400 000 years ago, a vast glacial lake in the North Sea basin spilled over its banks and triggered a catastrophic flood, unleashing water at roughly the rate at which Lake Erie surges over Niagara Falls today. The water quickly overwhelmed a ridge of Cretaceous period sedimentary rocks, mostly white chalk, between what is today southeastern England and northern France. For the first time, the island of Great Britain separated from the European continent...
In April a team of geologists presented exciting new evidence from the floor of the Dover Strait that paints a clearer picture than ever of the great floods that isolated Britain from the rest of Europe. Much of the coverage of the Nature Communications study plugged the flooding episodes as the “original Brexit.”...
Since the first flood that formed the Dover Strait, isolation of Britain from the rest of Europe has happened periodically during eras of high, interglacial sea level, like today. The separation inhibited the free exchange across the divide of plants and animals—including humans, who were absent from the British Isles during the Last Interglacial period 125 000 years ago. By contrast, during the intervening cold periods, when sea level was as much as 120 m lower than today, Britain was connected both by the emergent channel and by the southern North Sea. That connection allowed free passage of animals and plants, albeit under cold-climate conditions. Britain was last connected in this way until about 8000 years ago in the North Sea, and we can expect it to be reconnected during future glacial periods.
Since the first flood that formed the Dover Strait, isolation of Britain from the rest of Europe has happened periodically during eras of high, interglacial sea level, like today. The separation inhibited the free exchange across the divide of plants and animals—including humans, who were absent from the British Isles during the Last Interglacial period 125 000 years ago. By contrast, during the intervening cold periods, when sea level was as much as 120 m lower than today, Britain was connected both by the emergent channel and by the southern North Sea. That connection allowed free passage of animals and plants, albeit under cold-climate conditions. Britain was last connected in this way until about 8000 years ago in the North Sea, and we can expect it to be reconnected during future glacial periods.
Two-stage opening of the Dover Strait and the origin of island Britain
- Nature Communications
- doi:10.1038/ncomms15101
Abstract
Late Quaternary separation of Britain from mainland Europe is considered to be a consequence of spillover of a large proglacial lake in the Southern North Sea basin. Lake spillover is inferred to have caused breaching of a rock ridge at the Dover Strait, although this hypothesis remains untested. Here we show that opening of the Strait involved at least two major episodes of erosion. Sub-bottom records reveal a remarkable set of sediment-infilled depressions that are deeply incised into bedrock that we interpret as giant plunge pools. These support a model of initial erosion of the Dover Strait by lake overspill, plunge pool erosion by waterfalls and subsequent dam breaching. Cross-cutting of these landforms by a prominent bedrock-eroded valley that is characterized by features associated with catastrophic flooding indicates final breaching of the Strait by high-magnitude flows. These events set-up conditions for island Britain during sea-level highstands and caused large-scale re-routing of NW European drainage.
