Photo Credit: theguardian

Once upon a time, geologists say, anyone could have walked from Dover in Britain to Calais in France. Looking at the vast chasm of water that rests between the two locations now makes it hard to believe that that was once true.

‘It happened in two stages’

Scientists who sought to explain the reason for the formation of Island Britain in the past had the theory that all it took was one process (rise in sea water levels) for the English Channel to form. Recent findings have raised questions as to the validity of the theory.

Led by Professors Sanjeev Gupta and Jenny Collier of the Imperial College in London, an international team consisting of French, British and Belgian scientists scoped out the underwater topography of the English Channel. The whole point for this mapping was to show how the chasm came to be. “We wanted to find evidence to back up the hypotheses that had been formulated before,” Professor Gupta said.

The researchers worked with the assumption that one there had been a ridge made of chalk that linked Britain to France. The ridge was thought to be made of chalk because of the residue left on the Dover Cliffs.

In the team’s paper published in the Nature Communications Journal, the researchers postulated that the separation occurred in two stages. The researchers wrote that the first phase involved the ridge’s erosion by a massive waterfall.

In their paper, Sanjay and his team postulated that the Cover-Calais ridge acted as a dam of sorts. The ridge, in the team’s estimation, held back water from rivers like the Thames and the Rhine. During the Ice Age some 450,000 years ago, a glacier was formed upstream so that in addition to supporting meltwater, the dam held an ice lake. When the Ice Age abated, the western side of the lake spilled over the dam-like ridge and eroded it on that side. Shallow valleys on the west side support this claim.

The waterfalls were so powerful and large, stated the scientists, that they created plunge pools about 450 feet deep and miles wide in diameter. As the water level fell behind the ridge, the waterfalls receded, and sediments were deposited on that western region and in the pools.

After a while, water again began to accumulate behind the dam as more ice sheets melted. It did not take long for the force of the water to partially erode the chalk ridge until it became shorter than the land masses bordering it. Water from The Lobourg Channel cut across the plunge pools which were shallow after sedimentation. It was released in a megaflood that covered the whole of the English Channel to which the Lobourg Channel supplied water. “We found streamlined walls on the [English] Channel, evidence that tremendous force has eroded them,” Gupta noted. The megaflood described is the second stage of the formation of Island Britain.

With the ridge covered by water, Britain was separated from France. Rising sea levels isolated the island more and thus secured the first and only geographical Brexit: Britain’s parting with Europe.