Nearly 450,000 years ago, when Earth was in the grip of an ice age, ice stretched right across the North Sea, from Britain to Scandinavia. The low sea levels meant that the entire English Channel was dry land, a frozen tundra landscape, crisscrossed by small rivers.

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 from Imperial College London and their colleagues from institutes in Europe 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. 

Ten years ago, the researchers from Imperial College London 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 by the team, working with their colleagues in Europe, now shows for the first time the details of how this chalk ridge in the Dover Strait, between Dover and Calais, was breached. New geophysical data collected by colleagues 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 authors of today’s study show 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 believe 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.

David Fuller's view

Our subscriber added the comment:

And we loved our independence ever since!

Yes, and I’m forecasting that our second natural Brexit process will be slightly less traumatic.