Megaflood left Britain unoccupied

A catastrophic megaflood separated Britain from France hundreds of thousands of years ago, changing the course of British history, according to new research.

3d perspective view showing details of Channel valley. The erosional scours carved into floor of valley are clearly evident. The smaller drainages cut into valley sides formed after the flood event by normal river processes.

Using high-resolution sonar waves the team - led by Sanjeev Gupta and Jenny Collier from Imperial College London - captured images of a huge valley tens of kilometres wide and up to 50 metres deep carved into chalk bedrock on the floor of the English Channel. The maps highlight deep scour marks and landforms which were created by torrents of water rushing over the exposed channel basin.

Dr Sanjeev Gupta, from the Department of Earth Science & Engineering at Imperial said: “This prehistoric event rewrites the history of how the UK became an island and may explain why early human occupation of Britain came to an abrupt halt for almost 120 thousand years.”

At its peak, it is believed that the megaflood could have lasted several months, discharging an estimated one million cubic metres of water per second. This flow was one of the largest recorded megafloods in history and could have occurred 450,000 to 200,000 years ago.

To the north of the channel basin was a lake which formed in the area now known as the southern North Sea. It was fed by the Rhine and Thames, impounded to the north by glaciers and dammed to the south by the Weald-Artois chalk ridge which spanned the Dover Straits.

It is believed that a rise in the lake level eventually led to a breach in the Weald-Artois ridge, carving a massive valley along the English Channel, which was exposed during a glacial period.

Dr Collier said: “The preservation of the landscape on the floor of the English Channel, which is now 30-50 meters below sea-level, is far better than anyone would have expected. It opens the way to discover a host of processes that shaped the development of north-west Europe during the past million years or so.”

The research is published in Nature.