Giant flood made UK an island

By Michael Kahn

LONDON (Reuters) - A huge flood hundreds of thousands of years ago cut Britain off from the rest of Europe and turned it into an island, according to a new study that offers clues to how England was settled.

Using high-resolution sonar waves, researchers mapped the floor of the English Channel and turned up images of an enormous valley tens of kilometres wide and up to 50 metres deep carved into chalk bedrock.

The images were similar to an area in the U.S. state of Washington where a megaflood some 15,000 years ago also created a landscape of distinctive land formations -- indicating that the same thing happened in Britain, the researchers said.

Scientists said the study provides the best evidence yet in the debate seeking to explain how the English Channel formed and cut Britain off from the rest of Europe.

"It showed us for the first time the existence of this huge valley in the centre of the English Channel," said Sanjeev Gupta, a researcher at Imperial College London. "You can identify a whole series of land forms that are indicative of erosion by catastrophic flooding."

Gupta said the flood likely occurred 450,000 to 200,000 years ago when the Rhine and Thames rivers fed a large lake in the area now known as the southern North Sea and may have lasted several months.

Glaciers blocked the lake to the north and a chalk ridge stretching from Dover to France dammed the water to the south, the researchers said in the study published in Nature on Wednesday.

The flood carved out a giant gap that filled with water when sea levels rose, leaving Britain separated from France, the researchers said.