Some 450,000 years ago, Britain and Europe shared what must have been one of the greatest waterfall spectacles of the age.
Researchers from Imperial College London studying geophysical data from the seabed between Dover in the U.K. and Calais in France, a section today known as the Dover Strait, have discovered evidence of massive waterfalls that once dotted an imposing land bridge connecting the two land masses. The formation, composed of the same chalk that was ripped away to reveal the modern White Cliffs of Dover, stretched 20 miles and reached heights in excess of 350 feet.
In a paper published in the journal Nature Communications, a team of researchers from Imperial College London reveal how this thin strip of land connecting Britain and Europe for over 10 million years reached its violent end.
"This was really one of the defining events for north west Europe — and certainly the defining event in Britain’s history," Professor Sanjeev Gupta, who led the study, said in a statement. "This chance geological event, if it hadn’t happened, would have meant Britain was always connected to the continent."
The beginning of the end for the Dover-Calais land bridge was caused by the presence of a vast glacial lake that began to form to the northeast of the formation. As the lake’s levels rose from meltwater and rivers, the chalk ridge became eroded and punctured by a series of massive waterfalls.
Researchers analyzing the seabed found evidence of seven massive plunge pools stretching in a straight line from the ports of Calais to Dover. So great was the force responsible for their creation that each pool spans more than a mile wide and was drilled more than 330 feet into solid rock.
"It would have been a cold world dotted with waterfalls plunging over the iconic white chalk escarpment that we see today in the White Cliffs of Dover," Dr. Jenny Collier, a co-author of the study said in a statement.
Over a period of time lasting perhaps as long as hundreds of thousands of years, the waterfalls weakened and eroded the land bridge, carving out vast parts of the English Channel. As recently as 160,000 years ago, a megaflood of epic proportions completely collapsed the land bridge and created the island we know as Great Britain today.
"We still don’t know for sure why the proglacial lake spilt over," Collier added. "Perhaps part of the ice sheet broke off, collapsing into the lake, causing a surge that carved a path for the water to cascade off the chalk ridge. In terms of the catastrophic failure of the ridge, maybe an earth tremor, which is still characteristic of this region today, further weakened the ridge. This may have caused the chalk ridge to collapse, releasing the megaflood that we have found evidence for in our studies."
The researchers plan to take core samples from the in-filled sediments in the plunge pools. By analyzing their age, they hope to be able to better narrow down the exact timeline of the land bridge’s destruction.
"The English Channel is the world’s busiest shipping lane and it has huge tidal currents," Gupta tolf the BBC. "It will be hugely challenging."