Rock-Ice Bridge & Glacial Lake, artist concept (credit: Imperial College London)
In what must have been some of the most dramatic geomorpholocial events ever, a glacial lake burst through a land-bridge consisting of chalk, rock, and ice in prehistoric Europe. The resulting cataracts carved the gap now existing between Britain and France. The remnants of the bursting dam have been uncovered in a study by the Earth Sciences Department at the Imperial College of London. The new research determined the events occurred at the end of an ice age more than 450,000 years ago and created the English Channel.
Initially, waterfalls from a chalk and ice dammed glacial lake, created by meltwater from a receeding ice-cap and rivers in northern Europe, breached the ridge at the Dover Strait producing episodes of mass erosion. Measurements of the bottom of the present-day English Channel revealed sediment-infilled depressions deeply incised into bedrock and interpreted as giant 'plunge pools' created by the massive waterfalls. These depressions provide an initial model for the erosion of the Dover Strait by the spillover, with plunge pool erosion, and subsequent dam breaching by mega-floods in a 2-step process. According to the college announcement:
"previously, the researchers 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. Now working with colleagues in Europe, they have shown the details of how this chalk ridge in the Dover Strait was breached. New geophysical data 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. Cross-cutting of the submerged landforms by a prominent eroded valley, characterized by features that are typically associated with catastrophic flooding, indicate the final opening of the Strait by high-magnitude floodings."
Pre-strait Landform, Cataract, & Plunge Pools with Flooding Map of English Channel (credit: Imperial College of London)
One of the lead researchers, Jenny Collier, noted:
"Based on the evidence that we’ve 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."
A brief explanation of the pre-channel, tundra environmental was included with the report.
The complete Imperial College study is available here.