450,000BCE-200,000BCE: The Origins of Island Consciousness – the torrent that created the English Channel

Seven Sisters, by Homemade

From the BBC (published 18th July 2007) -

Some event, or combination of events, resulted in a huge lake breaching the chalk ridge between what is now Dover and Calais. Scars from the torrent are still evident in sonar images of the Channel floor today, presented (right) as a processed 3D perspective view.

Britain became separated from mainland Europe after a catastrophic flood some time before 200,000 years ago, a sonar study of the English Channel confirms.

The images reveal deep scars on the Channel bed that must have been cut by a sudden, massive discharge of water.

Scientists tell the journal Nature that the torrent probably came from a giant lake in what is now the North Sea.

Some event – perhaps an earthquake – caused the lake’s rim to breach at the Dover Strait, they believe.

Dr Sanjeev Gupta, from Imperial College London, and colleagues say the discharge would have been one of the most significant megafloods in recent Earth history, and provides an explanation for Britain’s island status.

“This event, or series of events, that caused [the breach] changed the course of Britain’s history,” Dr Gupta told BBC News.

“If this hadn’t happened, Britain would always have been a peninsula of Europe. There would have been no need for a Channel Tunnel and you could always have walked across from France into Britain, as early humans did prior to this event.”

Tremor trigger?

The idea of a great flood stems from scientists’ understanding of northern Europe’s ice age past.

It is believed that hundreds of thousands of years ago, when ice sheets had pushed down from Scotland and Scandinavia, there existed a narrow isthmus linking Britain to continental Europe.

This gently upfolding chalk ridge was perhaps some 30m higher than the current sea level in the English Channel.

Palaeo-researchers think it bounded a large lake to the northeast that was filled by glacial meltwaters fed by ancient versions of the rivers Thames and Rhine.

Then – and they are not sure of the precise date – something happened to break the isthmus known as the Weald-Artois ridge.

“Possibly this was just the build-up of water behind. Possibly something triggered it; it’s well known today that there are small earthquakes in the Kent area,” explained Imperial’s Dr Jenny Collier.

Re-routing rivers

Either way, once the ridge was broken, the discharge would have been spectacular.

The Imperial College and UK Hydrographic Office study used high-resolution sonar waves to map the submerged world in the Channel basin.

The images detail deep grooves and streamlined features, the hallmarks of landforms that have been gouged by large bodies of fast-moving water.

At its peak, it is believed that the megaflood could have lasted several months, discharging an estimated one million cubic metres of water per second. And from the way some features have been cut, it is likely there were at least two distinct phases to the flooding.

“I was frankly astonished,” said Dr Collier. “I’ve worked in many exotic places around the world, including mid-ocean ridges where you see very spectacular features; and it was an enormous surprise to me that we should find something with a worldwide-scale implication offshore of the Isle of Wight. It was completely unexpected.”

The researchers tell Nature that the ridge breach and the subsequent flooding would have helped reorganise river drainage in northwest Europe, re-routing both the Thames and the Rhine.

Fossil filling

The megaflood theory has been around for some 30 years; but the sonar images represent the clearest narrative yet for the story.

Previous studies of prehistoric animal remains from the past half-million years have already revealed the crucial role the English Channel has played in shaping the course of Britain’s natural history.

The Channel has acted as a filter through time, letting some animals (including humans) in from mainland Europe but not others.

And even when water was locked up in giant ice sheets and sea levels plummeted, the Rhine and the Thames rivers would have dumped meltwater into a major river system that flowed along the Channel’s floor.

Scientists can see all of this influence written in the type and mix of British fossils they find at key periods in history.

Professor Chris Stringer is director of the Ancient Human Occupation of Britain (Ahob) project, which has sought to fill out the details of the British Isles’ prehistory.

“The timing and method of formation of the Channel has been a long-running argument – after all, it really makes Britain what it is today, geographically,” he commented.

“The evidence presented in this paper is spectacular. It certainly explains and reinforces the picture the Ahob project has been putting together of the increasing isolation of Britain from Europe after 400,000 years ago.”

From the BBC (published 26th September 2006) -

A study of prehistoric animals has revealed the crucial role of the English Channel in shaping the course of Britain’s natural history.

The Channel acted as a filter, letting some animals in from mainland Europe, but not others.

Even at times of low sea level, when Britain was not an island, the Channel posed a major barrier to colonisation.

This was because a massive river system flowed along its bed, UK researchers told a palaeo-conference in Gibraltar.

Today the English Channel is 520km long, 30-160km wide, about 30-100m in depth and slopes to the south-west.

Even now, the bed of the Channel is incised by a network of valleys, the remains of the river system, which may have been cut by catastrophic drainage of meltwater from further north.

“It would have been an incredible barrier at times of high sea level, but it would also have been a formidable barrier at times of low sea level for populations trying to move south to north,” said Chris Stringer of London’s Natural History Museum.

Professor Stringer presented the results here at the Calpe conference, a meeting of pre-history experts from all over the world.

The big flood

The evidence comes from the Ancient Human Occupation of Britain Project (AHOB). This five-year undertaking by some of the UK’s leading palaeo-scientists has reassessed a mass of scientific data and filled in big knowledge gaps with new discoveries.

Chris Stringer’s co-researchers Andy Currant, Danielle Shreve and Roger Jacobi have been studying how the mammal fauna of Britain has changed over the last 500,000 years.

During that period, animals have colonised, abandoned and re-colonised Britain many times as the climate shifted from warm to cold and back to warm.

The Channel is thought to have formed during a cold period 200,000 years ago or more.

Meltwater from an ice sheet formed a lake, which then overflowed in a catastrophic flood – cutting through a chalk ridge that previously connected Britain to France.

Changes in climate were accompanied by changing sea levels. At the height of an ice age, these would have been low. During interglacial periods, when the climate was warm, sea levels rose.

But even when water was locked up in the ice sheets and sea levels plummeted, the Rhine and the Thames rivers dumped meltwater into a major river system that flowed along the floor of the Channel.

Unusual collections

This means that once the Channel formed, there was never again a simple land crossing to be made from northern France to Britain.

“We find we’re getting only a selection of the mammals during the British interglacials that there are in mainland Europe,” said Professor Stringer.

For example, at one pre-historic site, researchers found hippopotamus and fallow deer; but unlike mainland Europe at the time, there were no horses and no humans.

“This suggests that the Channel, or the Channel river system, is acting as a filter to prevent the movement of some of these [mammal] forms into Britain,” Professor Stringer added.

Once sea levels rose high enough for Britain to be an island, the select fauna that had made it across from mainland Europe could develop in extraordinary ways.

During one warm stage, about 80,000 years ago, fossils from Banwell Cave in Somerset show Britain was populated by some very unusual animals. These included reindeer, bison, and a giant bear similar to a polar bear.

Interestingly, there are no hyena fossils at Banwell Cave, as there were in mainland Europe. Instead, it appears, their role in the food chain may have been taken up by wolves.

“The wolves were developing much larger jaws. Their teeth show incredible signs of breakage and wear as if they’re chomping bones like hyenas,” said Professor Stringer.

The mammals at Banwell seem to be the kinds of animals normally found today in cold regions. But they lived in Britain during a warm stage and seemed to be adapting to their new environment.

The team thinks the antecedents of these animals must have arrived in Britain when the climate was cold. But when conditions warmed up, sea levels rose and isolated Britain, marooning this cold-adapted fauna in a warm land.