Catastrophic megaflood cut Britain off from France
A catastrophic megaflood which swept through the English Channel hundreds of thousands of years ago was responsible for cutting Britain off from mainland Europe, according to new research. Writing in the journal Nature, Sanjeev Gupta of Imperial College London and colleagues provide the first direct evidence that the English Channel was carved out by a sudden and massive flood, and not by fluvial processes, tidal scour or glacial erosion as others have proposed. 'This prehistoric event rewrites the history of how the UK became an island and may explain why early human occupation of Britain came to an abrupt halt for almost 120 thousand years,' commented Dr Gupta. 450,000 years ago the landscape of northern Europe looked very different to today. At that time, a vast lake covered what is now the southern part of the North Sea. Fed by many European rivers, including the Rhine and the Thames, this lake was hemmed in by glaciers to the North and the European landmass to the South. At its south-west corner, it was dammed by the narrow Weald-Artois chalk ridge, which spanned what is now the Dover Strait. The researchers believe that a rise in the level of this ancient lake lead to a breach in the ridge, triggering an epic flood which carved a massive valley through what is now the English Channel. The flood may have lasted several months, and at its peak a million cubic metres of water per second could have swept through the gap. Proof of this flood comes in the form of maps based on high resolution sonar measurements taken in the Channel. These show a huge valley, tens of kilometres wide and up to 50 metres deep. The deep scour marks and landforms could only have been formed by torrents of water rushing over the exposed Channel basin, the researchers state. With the breach of the Weald-Artois ridge, Britain's island fate was sealed. This prevented both humans and animals from reaching Britain for many millennia. Furthermore, the flood significantly reorganised river drainage systems in north-western Europe, and the sudden flow of large amounts of freshwater into the Atlantic would have affected ocean circulation patterns and ultimately the climate. 'The preservation of the landscape on the floor of the English Channel, which is now 30-50m below sea level, is far better than anyone would have expected,' said Jenny Collier of Imperial College, who participated in the study. 'It opens the way to discover a host of processes that shaped the development of north-west Europe during the past million years or so.'
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