Scientists, including one of Indian origin, have found evidence of a 'geological Brexit' that happened about 450,000 years ago when ancient Britain separated from the rest of the Europe.
Researchers from Imperial College London in the UK and colleagues have worked out how a thin strip of land that once connected ancient Britain to Europe was destroyed.
Britain's separation from mainland Europe is believed to be the result of spill over from a proglacial lake — a type of lake formed in front of an ice sheet — in the North Sea, but this has remained unproven.
Now, researchers show that the opening of the Dover Strait in the English Channel occurred in two episodes, where an initial lake spill over was followed by catastrophic flooding.
Previously, the researchers had revealed geophysical evidence of giant valleys on the seafloor in the central part of English Channel.
They believed these valley networks were evidence of a megaflood gouging out the land, which they speculated may have been caused by a catastrophic breach in a chalk rock ridge joining Britain to France.
The new study shows for the first time the details of how this chalk ridge in the Dover Strait, between Dover and Calais, was breached.
"The breaching of this land bridge between Dover and Calais was undeniably one of the most important events in British history, helping to shape our island nation's identity even today," Professor Sanjeev Gupta from the Department of Earth Science and Engineering at Imperial, said.
"When the ice age ended and sea levels rose, flooding the valley floor for good, Britain lost its physical connection to the mainland. Without this dramatic breaching Britain would still be a part of Europe. This is Brexit 1.0 - the Brexit nobody voted for," said Gupta.
Geophysical data collected from Belgium and France has been combined with seafloor data from the UK showing evidence of huge holes and a valley system located on the seafloor.
The team show that the chalk ridge acted like a huge dam and behind it was a proglacial lake.
This lake was first hypothesised by scientists more than 100 years ago and the new study shows how the lake overflowed in giant waterfalls, eroding the rock escarpment, weakening it and eventually causing it to fail and release huge volumes of water onto the valley floor below.
The team believes that the huge holes that they analysed on the seafloor are plunge pools, created when water cascading over an escarpment hit the ground and eroded rock.
The plunge pools in the Dover Strait are huge — up to several kilometres in diameter and around 100 metres deep and were drilled into solid rock.
Around seven plunge pools run in a line from the ports of Calais to Dover.
The researchers suggest these plunge pools are evidence of an overflow of water from the lake in the southern North Sea.
The straight line of the plunge pools suggests they were cascading off one single rock ridge perhaps 32 kilometres long and 100 metres high — the land bridge between Europe and the UK.
"Based on the evidence that we have seen, we believe the Dover Strait 450,000 years ago would have been a huge rock ridge made of chalk joining Britain to France, looking more like the frozen tundra in Siberia than the green environment we know today," Jenny Collier, from the Department of Earth Science and Engineering at Imperial, said.
"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," said Collier.
The research was published in the journal Nature Communications.
