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Ancient floods split Britain from rest of Europe

Water gushes carved away a land bridge, delaying for ages human migration, study finds.

July 19, 2007|Amber Dance | Times Staff Writer

Scientists using sonar to probe the floor of the English Channel have found that Britain was sliced from the European continent by massive prehistoric floods that cut it off from human migration for 120,000 years.

The new research, published today in the journal Nature, found evidence of at least two floods between 180,000 and 450,000 years ago.

The months-long gushes of water cut through the island's chalky land bridge to Europe "like a buzz saw through Styrofoam," said Steven Dutch, a geologist at the University of Wisconsin-Green Bay who was not associated with the study.

The mega-floods broke through at the present Straits of Dover, the narrowest part of the channel, leaving the white cliffs of Dover where the bridge once began.

For The Record
Los Angeles Times Friday July 20, 2007 Home Edition Main News Part A Page 2 National Desk 1 inches; 38 words Type of Material: Correction
English Channel floods: An article in Thursday's Section A about how Britain was sliced from the European continent said that the Scablands floods were caused by glacial lakes in Idaho. The lakes were in what is now Montana.

"That land bridge had been there for 13 million years," said Philip Gibbard, a geologist at the University of Cambridge, who was not part of the study.

The researchers' map of the seabed found a valley that was miles wide and more than 150 feet deep in some places. They also saw scour marks, layers and islands carved in the rock, said Sanjeev Gupta, lead author of the study and a geologist at Imperial College London.

Gupta compared the features with those of the Scablands in eastern Washington state -- a scarred region covering thousands of square miles, comprising deep, dry canyons, giant holes and scattered boulders.

The region is a geological example of a landscape formed by mega-floods. The Scablands floods took place thousands of years ago, when glacial lakes in Idaho drained into the area. To a geologist, the most striking feature of the Scablands is the ripples.

"This looks just like what you'd see in a stream, but it's scaled up 100 times," Dutch said. "There are places where you can see ripple marks that are 50 feet crest to crest."

The bottom of the English Channel has similar features that could only come from a giant flood, the scientists said.

The researchers surmised that the source of the flooding was a lake in the region of the modern North Sea that overflowed because advancing glaciers blocked water from draining elsewhere.

The water poured out at a rate of more than 250 million gallons per second, the scientists said.

The mega-floods altered Britain's course in history, cutting early humans off from the island and temporarily halting migration.

"Between 180,000 years ago and 60,000 years ago there's actually no evidence for humans living in Britain," Gupta said.

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amber.dance@latimes.com

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