Huge Flood Cut Britain From Europe

July 18, 2007 — Britain is an island thanks to a megaflood that dug out the English Channel, according to a study released on Wednesday by the journal Nature.

The catastrophic flood, one of the mightiest in recorded history, occurred between 450,000 and 200,000 years ago and created a barrier to human migration to Britain that probably lasted for tens of thousands of years.

Imperial College London researchers Sanjeev Gupta and Jennifer Collier used high-resolution sonar to build up a highly detailed picture of the floor of the Channel.

They captured spectacular images of a vast submerged valley, dozens of miles wide and up to 165 feet deep, that was carved into the Channel's chalky bedrock.

They believe the valley is the flood-scoured remnant of a land bridge that was destroyed when a natural dam, running across what is now the Dover Straits, was breached.

This so-called Weald-Artois ridge was the southern wall of a gigantic lake which spanned what is now the southern North Sea.

Two rivers, the Rhine and the Thames, fed the great lake, and towering glaciers provided its northern wall.

The Weald-Artois ridge collapsed, presumably because of a rise in the lake's level, unleashing a megaflood that lasted for several months. Thirty-five million cubic feet of water per second poured southwards, Gupta and Collier calculate.

The torrent formed the "Channel River," digging out what is now a valley on the Channel floor.

At that time, Earth was in a glacial period. Sea levels were much lower than they are today, as so much water was locked up in icesheets.

When the ice age came to an end, sea levels rose once more and the valley was permanently drowned, leaving today the sister cliffs of Dover and Cap Gris-Nez as signatures that Britain and France were once joined.

In addition to changing the region's topography forever, the "Channel River" must also have altered the course of human history, the paper suggests.

"This prehistoric event rewrites the history of how the United Kingdom became an island and may explain why early human occupation of Britain came to an abrupt halt for almost 120,000 years," suggests Gupta.