How Flood Turned Britain Into An Island

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How flood turned Britain into an island

 

http://www.timesonline.co.uk/tol/news/uk/s...l&offset=12

(Richard Pohle/The Times)

 

The cliffs at Dover and the English Channel

Mark Henderson, Science Editor

 

Britain was turned into an island by an enormous flood that opened the Channel and changed the course of history, scientists have discovered.

 

Some time between 450,000 and 200,000 years ago, a natural land dam at the Strait of Dover failed, sending a wall of water surging into the once-dry basin that is now the Channel bed, with at least ten times the destructive power of the Indian Ocean tsunami, and redrawing the map of Europe.

 

Anything in the floodwater’s path would have been obliterated, as a discharge 100,000 times greater than that of the River Thames flowed through the breach.

 

It was one of the most severe floods known, according to research published in the journal Nature.

 

The legacy was the vast Channel river, which at its height drained half the waterways of Europe into the Atlantic, and cut Britain off from the rest of the Continent.

 

When the ice sheets that covered the British Isles and Scandinavia later melted, the entire basin was flooded to create the Channel as it is today.

 

Without this dramatic chain of events, which has been revealed by a new high-resolution sonar survey of the Channel floor, it is entirely possible that Britain would never have become an island or developed the seafaring culture that eventually turned much of the global map pink.

 

While scientists do not yet understand what triggered the megaflood. one possibility is that it was started by a small earthquake at a moment when summer meltwaters in what is now the North Sea were high.

 

Jenny Collier, of Imperial College, London, a leader of the study team, said: “This was the event that finally made us an island, and therefore gave us our unique historical development.

 

“We don’t actually know why the dam failed. It is possible that it was the pressure of rising water and that it would have happened anyway, but there are little earthquakes in that area — there was one recently in Kent — and it is a tantalising possibility that one triggered the flood.

 

“It might never have happened, and Britain would have gone through history always joined to Europe.”

 

One consequence was to cut Britain off from the European mainland even during periods of heavy glaciation when sea levels were low, making it much harder for early humans to settle what was previously a peninsula.

 

This, in turn, seems to have contri-buted to a population crash. While there is evidence of habitation by Homo heidelbergensis and Neanderthal Man from 700,000 years ago to about 180,000 years ago, there is none for 120,000 years after that.

 

Researchers believe that as isolated Neanderthal communities grew sparse, the Channel or Channel river made it impossible for others to move north to repopulate the island.

 

While it has long been known that Britain was once joined to the Continent during glacial periods when sea levels were lower than today, the origins of the Channel have remained controversial, with some experts preferring a flood hypothesis and others favouring gradual erosion.

 

The new analysis led by Dr Collier and her colleague, Sanjeev Gupta, shows that a flood was responsible, and not just any flood at that. The first of two vast inundation events, it was one of the largest recorded in history.

 

About 450,000 years ago the Channel was a basin known as an embayment, which was periodically flooded when sea levels were high but was otherwise dry land.

 

The southern part of the modern North Sea was a lake fed by meltwater from the British and Scandinavian ice sheets, and by the Thames and Rhine river systems.

 

The chalk ridge of the Weald ran continuously into the Artois region of northern France and Belgium, and this held back the waters of the North Sea lake.

 

The new high-resolution sonar scans have shown that at some point during the next 250,000 years, this natural dam broke. The force can be seen in the gouges and scour marks at the bottom of the Channel, which cannot be explained by any other process.

 

The event also carved out one of Britain’s most iconic geographical features — the White Cliffs of Dover — and rerouted the Thames and the Rhine so that both fed the Channel river.

 

Only when sea levels rose as the world emerged from glaciation did these rivers again flow into the North Sea as they do today.

 

Dr Gupta said: “This prehistoric event rewrites the history of how Britain became an island and may explain why early human occupation of Britain came to an abrupt halt for almost 120,000 years.”

 

Professor Chris Stringer, of the Natural History Museum, who heads the Ancient Human Occupation of Britain Project, said: “We know of ancient humans 700,000 years ago at Pakefield, 500,000 years ago at Boxgrove, 400,000 years ago at Swanscombe and 220,000 years ago at Pontnewydd, but there is no evidence beyond 180,000 years ago until around 60,000 years ago.”

[woodsmoke]

Awesome stuff; sounds a lot like the megaflood that created the Scablands in Washington.