FLOODING LEFT BRITAIN AN ISLAND

[Bianca]

STUDY:  FLOODING LEFT BRITAIN AN ISLAND
 






By THOMAS WAGNER, Associated Press Writer
 
LONDON - One of Earth's largest-ever floods broke apart a strip of land connecting what is now Britain and France, permanently separating them, researchers say.
 
The flood unleashed about 35 million cubic feet of water per second, 100 times greater than the water discharge of the Mississippi River.

The natural disaster, which occurred about 400,000 years ago during a glacial period, was later followed by rising sea levels that created what is now the English Channel, the study says.

It is not known if humans died during the disaster, but the study says the flooding may have ended migration by early humans and mammals such as horses across the land, which was at least 28 miles wide.

The theory that Britain became an island during a catastrophic flood — rather than through the course of normal erosion — was first proposed in the 1980s. The new study, outlined in the journal Nature, used high-resolution sonar data that were previously unavailable to produce three-dimensional, high-quality imagery of the region.

In a commentary in the journal, Philip Gibbard, a University of Cambridge geologist who was not involved in the study, praised the research. "It is no exaggeration to say that this Channel flood was probably ... one of the largest ever identified ... (and) it had profound long-term geographical consequences," he wrote.

Another outside expert, Chris Stringer, a paleontologist at the Natural History Museum, also welcomed the report.

"The timing and method of formation of the Channel have been a long-running argument — after all it really makes Britain what is today, geographically — and the evidence presented in this paper is spectacular," Stringer said.

He said it explains and reinforces the picture his museum's "Ancient Human Occupation of Britain" project is putting together about the increasing isolation of Britain from Europe after 400,000 years ago.

The study — by three scientists at Imperial College London and an official at the UK Hydrographic Office — says the megaflood occurred during the first major extension of a continental ice sheet into lowland central Europe and Britain.

The ice advanced across the emergent North Sea floor from southern Scandinavia, blocking rivers flowing northward into the Atlantic and causing a gigantic glacial lake to develop in front of it, dammed by higher ground to the south and fed by the drainage of much of Western Europe.
 When this dam overflowed, it produced a huge deluge that quickly broke apart the land mass connecting what is now England and France.

The glacier eventually withdrew from the area, but about 160,000 years ago, during a second significant glaciation, another ice sheet reached central Netherlands and again dammed a lake in the southern Northern Sea, the study says.

When this barrier broke it produced a vast volume of water that surged through the land gap, dramatically deepening it to about its current level and sealing Britain's fate as an island.

The study also says the two almost instantaneous releases of huge volumes of fresh water into the Atlantic may have triggered changes in ocean circulation that in turn may have affected the climate of the entire North Atlantic region.

http://news.yahoo.com/s/ap/20070719/ap_on_sc/britain_megafloods;_ylt=AtAhWU6xrDadLpC7SWklVXJxieAA

[Manetho]

 Megaflood Created Great Divide Between Britain and France
Dave Mosher
LiveScience Staff Writer
LiveScience.com
Wed Jul 18, 1:25 PM ET
 


The cultural rift between Britain and France endures as an amusing mystery for many, but the physical divide between them can now be blamed on two ancient floods.

 
About 450,000 years ago, a "megaflood" breached a giant natural dam near the Dover strait and began the formation of the English Channel , according to a study detailed in the July 19 issue of the journal Nature. Following this first disastrous flood, a second deluge finished the job.


"The first was probably 100 times greater than the average discharge of the Mississippi River," said Sanjeev Gupta, a geologist at Imperial College London and co-author of the study. "But that's a conservative estimate—it could have been much larger."


Gupta said his team's findings quash previous, evidence-thin theories about how the island became severed from mainland Europe.


"Britain has been an island for only a very short time period, and we've put together the first clear evidence that the valley system in the English Channel was carved by a megaflood," Gupta said.


Chalky dam


Prior to the first megaflood, which originated from an enormous lake of freshwater in what is now the North Sea, a quaint river valley was the only waterway obstructing France and Britain. Inattentive to building materials, nature contained the monstrous, ice-locked lake with chalky stone.


"Some freak event, whatever it was, caused the dam to fail at some point," Gupta said, although he noted that the breach may have resulted from simply too much water built up behind the dam.


When the 19-mile-wide barrier failed, the deluge that followed carved an impressive basin 33 feet deep and almost 31 miles wide in a matter of weeks.


"The dimensions are enormous," Gupta said. "This was when sea levels were about 100 meters (328 feet) lower than today, when a lot of ocean water was locked up in ice sheets."


Double deluge


An even larger and more cataclysmic event, however, outdid the first megaflood, sometime prior to 180,000 years ago. This second deluge created the characteristic English Channel bottom seen today, according to the study.


The second torrent added insult to injury, whittling polished mesa-like islands out of the basin floor. Gupta said such structures are tell-tale signs of megafloods.


"The Channeled Scablands, in eastern Washington state, is an area where a huge ice-dammed lake created some of these extraordinary features," Gupta said. "They're analogous to what we see underwater in the English Channel."


Gupta is uncertain what initiated the second megaflood, but he thinks a large embankment of glacial deposits could have released freshwater that etched out canyon-like valleys.


Old evidence, new discovery


Making the discovery, Gupta explained, arose out of sheer boredom.


"I went to the library and came across an older book laying out this theory," Gupta said, noting that the author had little evidence to support it. Yet Gupta realized advances in sonar technology allowed mapping the English Channel's floor in high-resolution, which was done for purposes of ship safety. It was simply a matter of bringing the two pieces together, he pointed out.

"We were astonished by what we found. Quite frankly, we have better maps of Mars than we do of shallow seas around Britain," he said.

Gupta explained three dominant English-Channel-forming theories are shored up by the findings. Glaciers couldn't have carved out the Channel because the polar ice sheets never crept that far south. He explained that erosion by river or ocean also can't account for the underwater valley because it is too wide and has structures characteristic of a major flood.

"The valley cuts across a large number of rock types, simply ignores the different layers," he said, explaining that only a rapid, enormous and powerful flood can account for the bedrock-scouring features.

In the future, Gupta and his team plan to look for remnants of the enormous natural dam.

"We want to map the ancient lake out, see if there are any other features we've missed," Gupta said. "We may be able to find large boulders left behind from the dam. Be prepared for big discoveries in the future—this is a whole new avenue of research."


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Original Story: Megaflood Created Great Divide Between Britain and France
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[Manetho]

Nice find, Bianca, I like your graphics!