The scientists explained when Earth was in the grip of an ice age , years ago ice stretched right across the North Sea from Britain to Scandinavia. Low sea levels meant the entire English Channel was dry, a frozen tundra landscape crisscrossed by small rivers much like modern day Siberia. The chalk rock ridge between Dover and Calais held back a pro-glacial lake — a type of lake formed in front of an ice sheet — in the North Sea.
The scientists found seven plunge holes over a mile wide and feet deep in a straight line suggesting these were from the lake in the southern North Sea cascading off one single rock ridge that formed a land bridge. But then surge water from the lake caused this ridge to give way and and fully opened the Dover Strait hundreds of thousands of years later. This tidal wave created a new valley system, the Lobourg Channel along the seabed of the English Channel.
This is Brexit 1. Further research will try and establish a timeline which will allow scientists to learn more about the distinctive evolution of Britain, compared to mainland Europe. As it turns out, Brexit was not the first time Britain has separated from the European mainland.
Scientists say that England and France were once connected by a ridge of land, until powerful waterfalls from an overfull lake demolished their connection. An earlier version of this story said the plunge pools were hundreds of kilometers deep; they were hundreds of meters deep. Some , years ago, Europe was a very different place. The English Channel was not a wide strip of water separating present-day England and France, but instead a frozen, river-ribboned tundra connecting the two lands.
The debate over how the dry tundra turned into a wide waterway has dogged scientists for decades. Was it a sudden change or a gradual process? Discovered in the s while engineers were surveying the sea floor, these depressions could stretch roughly seven kilometers wide and hundreds of meters deep.
These pits had been filled with looser sediment, forcing officials to reroute construction of the Channel Tunnel. In the s, Bedford College marine geologist Alec Smith suggested that powerful, prehistoric waterfalls dug those enormous holes, but at the time, scientists lacked the data to determine whether this idea was true.
Their analysis shows that Britain was once connected to the mainland thanks to a chalk ridge that extended from Dover home of the famous white-chalk cliffs in England to Calais in France, right across the Dover Strait.
This ridge kept a proglacial lake — a lake formed in front of a glacier — at bay, until some unknown event caused it to spill over the natural dam, plunging into the valley below. This must have occurred at several spots along the ridge, leaving the telltale string of seven or so oversized plunge pools stretching from Dover to Calais. Perhaps a chunk of ice broke off the glacier and plunged into the lake, causing it to slosh over the ridge like sugar cubes dropped into a generous cup of tea.
But the authors suggest that a second, more catastrophic breach subsequently occurred — possibly hundreds of thousands of year later, irrevocably separating Britain from Europe. This final collapse of the land bridge is marked out by a larger seafloor channel named the Lobourg Channel, which cuts through the earlier structures. This appears to have been carved by a major cataclysmic flood from the North Sea into the English Channel.
The timings of the two-stage erosion, including the final destruction of the connecting bridge, are uncertain, but mollusc shells found either side of the breach indicate that it was complete at least , years ago. The latest observations are the result of a broad marine geophysics campaign to tackle the problem. Ship-based seismic surveys of the floor of the English Channel have been combined with a type of sonar to provide an astoundingly detailed picture of the sea floor and its sub-surface.
Uncertainty remains over the exact timings of each of the events, and researchers have set their sights on drilling into the sea floor to retrieve samples from the plunge pool sediments to determine their precise ages. The erosion of the land bridge hundreds of thousands of years ago set Britain on its path to becoming an island nation. Portsmouth Climate Festival — Portsmouth, Portsmouth.
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