Storegga Slide

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 Sea, 100 km north-west of the Møre coast. An area the size of Iceland slumped, causing a very large tsunami in the North Atlantic Ocean. This collapse involved an estimated 290 km length of coastal shelf, with a total volume of 3,500 km³ of debris.cite journal | first = Stein | last = Bondevik | coauthors = Dawson, Sue; Dawson, Alastair; Lohne, Øystein | year = 2003 | month = 5 August | title = Record-breaking Height for 8000-Year-Old Tsunami in the North Atlantic | journal = EOS, Transactions of the American Geophysical Union | volume = 84 | issue = 31 | pages = 289, 293| url = http://www.ibg.uit.no/~stein/Bondevik-al-03-EOS.pdf | accessdate = 2007-01-15] Based on carbon dating of plant material recovered from sediment deposited by the tsunami, the latest incident occurred around 6100 BC. [cite conference | author=Bondevik, S; Lovholt, F; Harbitz, C; Stormo, S; Skjerdal, G | title=The Storegga Slide Tsunami - Deposits, Run-up Heights and Radiocarbon Dating of the 8000-Year-Old Tsunami in the North Atlantic | booktitle=American Geophysical Union meeting | year=2006 | pages=] In Scotland, traces of the subsequent tsunami have been recorded, with deposited sediment being discovered in Montrose Basin, the Firth of Forth, 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 reoccurrence 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.

References

External links

* [http://www.hydro.com/ormenlange/en/about_ormen/key_features/storegga_slide/index.html The Storegga slide investigation, including animations]