Megaflood Created Great Divide Between Britain and France

About 450,000 years ago, a "megaflood" breached a giant natural dam near the Dover strait and began the formation of the English Channel , according to a study detailed in the July 19 issue of the journal Nature. Following this first disastrous flood, a second deluge finished the job.

"The first was probably 100 times greater than the average discharge of the Mississippi River," said Sanjeev Gupta, a geologist at Imperial College London and co-author of the study. "But that's a conservative estimate—it could have been much larger."

Gupta said his team's findings quash previous, evidence-thin theories about how the island became severed from mainland Europe.

"Britain has been an island for only a very short time period, and we've put together the first clear evidence that the valley system in the English Channel was carved by a megaflood," Gupta said.