(CN) – Britain’s vote to leave the European Union this past summer wasn’t the first time the British Isles have separated from the continent: 450,000 years ago, the land bridge that joined them was obliterated by chance geological events that severed their physical connection forever.
Nearly 450,000 years ago, an ice age gripped the planet. Ice stretched across the North Sea from Britain to Scandinavia, and the resulting lower sea levels meant the entire English Channel was dry frozen tundra marked by small rivers.
Researchers have long theorized that a massive chalk ridge in the Dover Strait, between Dover and Calais, France, held back a huge lake that had formed in front of the ice sheet. Ten years ago, researchers from the Imperial College London found geophysical evidence of megaflood erosion beneath the English Channel which they believed at the time was caused by a catastrophic breach of the chalk ridge.
Now in a new study, the team and their colleagues in Europe offer details on the ridge’s breach – which first began as waterfalls when the proglacial lake overflowed. The waterfalls eroded the rock at the foot of the chalk ridge, drilling plunge pools several kilometers in diameter and around 100 meters deep into solid rock.
The plunge pools form a straight line, further bolstering the belief that the chalk ridge – the land bridge connecting Britain and Europe – held back the proglacial lake. The researchers believe the ridge was about 20 miles long and 328 feet tall until the constant pounding of the waterfalls caused it to collapse.
It’s taken the researchers 10 years to put together the geological jigsaw puzzle, but they say they’re confident they now know what caused “Brexit 1.0.”
“We still don’t know for sure why the proglacial lake spilt over,” study co-author Jenny Collier said. “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 say that but for whatever chance geological event caused the lake to spill over, Britain might have remained connected to Europe – jutting out into the sea as Denmark does. They didn’t hypothesize whether remaining physically connected to Europe would have changed the results of the June 2016 vote to leave the European Union.
They plan to take core samples of the filled-in plunge pools to figure out when the event occurred. However, they noted the challenge of their next undertaking – huge tidal changes occur in the Dover Strait, which is also the world’s busiest shipping lane.