Megaflood in English Channel separated Britain from France

edyong — Mon, 08 Jun 2009 06:30:27 +0000

Hundreds of thousands of years ago, one of the largest floods in Earth's history turned us into an island and changed the course of our history. Britain was not always isolated from our continental neighbours. In the Pleistocene era, we were linked to France by a land ridge called the Weald-Artois anticline that extended from Dover, across what are now the Dover Straits.

This ridge of chalk separated the North Sea on one side from the English Channel on the other. For Britain to become an island, something had to have breached the ridge.

Now, Sanjeev Gupta and colleagues from Imperial College London have found firm evidence that a huge 'megaflood' was responsible. They analysed a hidden series of massive valleys on the floor of the English Channel - vast gouges of bedrock 50 metres deep and tens of kilometres wide.

These valleys were first noticed by geologists in the 1970s but until now, no one really knew what caused them. Gupta decided to find out with the help of some modern technology. He used high-resolution sonar to create a contour map of the Channel floor, and found that this hidden world was remarkably well preserved.

He saw a clear picture of the huge, linear valleys, branching out in a westerly direction. In and among the valleys lay long ridges and grooves running parallel to the channel, V-shaped scours that taper upstream, and streamlined underwater islands up to 10km long.

All in all, these images show that the valleys are geological scars, formed by erosive torrents of water travelling west from the Dover straits. Their size and features are consistent with a massive flood, carving out the land in its wake.

During the Pleistocene, the North Sea was actually a giant lake, closed off at its northern edge by merged ice sheets from Britain and Scandinavia, and at its southern edge by the Weald-Artois ridge.

This lake was fed by both the Thames and the Rhine rivers. That, combined with the melting ice, eventually burst the Weald-Artois barrier, sending the lake's water surging into the Channel.

Gupta estimated that the flood would have lasted for several months and involved at least two episodes. At its peak, one million cubic metres of water flowed into the Channel every second, a thousand times more than the Victoria Falls.

The megaflood changed both the local geography and the course of British history. It reorganised the drainage of the Thames and Rhine rivers to the Channel rather than the North Sea. And most importantly, it permanently separated Britain from continental Europe.

The flood made migration into the newborn island more difficult and aside from some early attempts at settlement, Britain was completely devoid of humans for about 100,000 years.

Once humans finally colonised this green and pleasant land, our island status has affected our entire history from our power as a naval empire, to our strategies during the Second World War to our national character.

Reference: Gupta, Collier, Palmer-Felgate & Potter. 2007. Catastrophic flooding origin of shelf valley systems in the English Channel. Nature 448: 342-346.

edyong Mon, 06/08/2009 - 02:30

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Earth sciences

Britain

English Channel

Europe

flood

france

megaflood

I went to a lecture about 10? years ago, where this theory was put forward. Seems it took a while to be accepted...

How long ago is the estimate for the flood? Interesting post!

I am now living near to glacial Lake Agassiz, where in places there are clearly marked shorelines. Presumably the North Sea was higher than normal sea level so there should be traces of the ancient shoreline. Is there anywhere where these have been found?

Oh, cool! I'm glad you re-posted this one - I hadn't known that the North Sea had been an ice-dammed lake, and I didn't know the structures and/or geomorphology that makes Britain an island. Thank you!

Countdown to some random crationists use this as evidence for Noah's flood: 5... 4... 3...

Interesting, where was the Northern shores of the "North Sea Lake" ? There is presumably a series of shallows somewhere, around the Dogger Bank perhaps, further North it would seem to be deeper. And also, this implies that the sea level itself was a lot lower, so was this during an ice age or recently after ?

So that's another giant flood event for Eurasia. Pretty awesome, and it makes me think what's going to happen in the next decade or so, what with all the major glaciers in the world melting at record rates...

Great post, Ed.

@Zach There's simply not enough ice or big enough glaciers left impound big lakes to create the sort of flooding we saw at the end of the Pleistocene.

#1>Seems it took a while to be accepted...
I've heard that the vatican has recently forgiven Galileo for his heretical fantasies.
"Earth revolve around the sun? Never!"

I had heard this theory long ago, and I just assumed it was well accepted. I didn't know that there was some controversyâthat's how science works!

This article is fascinating enough, but to imagine world history if this hadn't happened takes it to another level. Maybe William the Conqueror would have been an English subject because Normandy was connected to England, and we would be speaking some ancient Germanic tongue rather than a Anglo-French patois. Maybe Spain wouldn't have needed an Armada and defeated Elizabeth I in a battle at Calais. Maybe England wouldn't have become a huge naval power, the the US speaks Dutch. And, of course, Hitler wouldn't have stopped at the English Channel.

I'm going to ignore the random creationists, and think about how the alternative history writers will have fun with this over the next few years.

I thought that in subsequent ice ages (lke the last glacial maximum 21000 yrs ago) the sea level had again fallen so that there was a land bridge with France and the Netherlands as recently as about 15000 years ago, when modern humans arrived. And Neanderthals got here before then. So this flood event was not the final isolation of Britain from Europe.

Paul

what blocked off the channel's southern end, and when did it open?

Nomen. I think that the North sea, at the time, was at a higher elevation. Once it carved out the path through the anticline, it flowed downhill to the Atlantic. The flooding waters then eroded the land, and as seas rose, it filled the eroded valleys.

At least, that's how I'm reading it.

So how does this fit with the new discovery of the dinosaur found on the coast of Dover?
Was the dinosaur in the sea dead before the great flood or after?

Mark

The dinosaur was dead before.