Half a million years ago England and France shared a land connection that also formed the dam for a glacial lake that covered much of northern Europe.
The soft chalk bedrock dam was breached by the waters of the glacial lake between 450 and 180 thousand years ago, forming the Strait of Dover. As with the torrent that breached the Straits of Gibraltar and filled the Mediterranean, modeling indicates that waters rushed through the Dover Strait at rates up to 1 million cubic meters per second.
The evidence for this rush of water comes from sonar imaging of the submerged valley carved by the flood waters. Broad grooves up to 100 meters wide and 15 km long were carved into the valley floor. These features indicate high flow rates, and are associated with other mega floods.
Source: Birth of an Island: Megaflood severed Europe from Britain. SN July 21, 2007, v. 172, p. 35; based on Gupta, S., et al., 2007. Nature July 19
Illustration credit: http://islesproject.com/2009/01/12/450000bce-200000bce-the-origins-of-island-consciousness-the-torrent-that-created-the-english-channel/
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