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The three Storegga Slides are considered to be amongst the largest known landslides. They occurred under water, at the edge of Norway's continental shelf (Storegga is Old Norse for the "Great Edge"), in the Norwegian Seamarker, 100 km north-west of the Møre coast. An area the size of Icelandmarker slumped, causing a very large tsunami in the North Atlantic Oceanmarker. This collapse involved an estimated 290 km length of coastal shelf, with a total volume of 3,500 km3 of debris. Based on carbon dating of plant material recovered from sediment deposited by the tsunami, the latest incident occurred around 6100 BC. In Scotlandmarker, traces of the subsequent tsunami have been recorded, with deposited sediment being discovered in Montrose Basinmarker, the Firth of Forthmarker, up to 80 km inland and 4 metres above current normal tide levels.

As part of the activities to prepare the Ormen Lange natural gas field, the incident has been thoroughly investigated. One conclusion is that the slide was caused by material built up during the previous ice age, and that a recurrence would only be possible after a new ice age. This conclusion is supported by numerous exhaustive published scientific studies.

Facts and arguments supporting this conclusion were made public in 2004. Earlier it was concluded that the development of the Ormen Lange gas field would not significantly increase the risk of triggering a new slide. A new slide, potentially larger than Denmark in area and 400–800 metres high, would trigger a very large tsunami that would be devastating for the coast areas around the North Sea and the Norwegian Sea.

Possible mechanism

Earthquakes, together with gases (e.g. methane) released from the decomposition of gas hydrates, are considered to be the likely triggering mechanisms for the slides. Another possibility is that the sediments became totally unstable and failed perhaps under the influence of an earthquake or ocean currents.

Impact on human populations

At the time of the last Storegga Slide, a land bridge known to archaeologists and geologists as "Doggerland" existed, linking Great Britainmarker with Denmarkmarker and the Netherlandsmarker across what is now the southern North Seamarker. This area is believed to have included a coastline of lagoons, marshes, mudflats, and beaches, and to have been a rich hunting, fowling and fishing ground populated by Mesolithic human cultures. Although the conventional view has been that Doggerland was submerged through a gradual rise in sea level, it has been suggested instead that much of the land was inundated by a tsunami triggered by the Storegga Slide, thus helping to create the island of Great Britain. This event would have had a catastrophic impact on the contemporary coastal Mesolithic population, and separated cultures in Britain from those on the European mainland.

References

  1. "Doggerland Project", University of Exeter Department of Archaeology
  2. Vincent Gaffney, "Global Warming and the Lost European Country"
  3. "Britain's Drowned World", Time Team, Channel 4 Television, 24 April 2007
  4. Bernhard Weninger et al., The catastrophic final flooding of Doggerland by the Storegga Slide tsunami, Documenta Praehistorica XXXV, 2008



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