Storegga Slide

The three Storegga Slides were large landslides. They occurred under water, at the edge of Norway's continental shelf, in the Norwegian Sea. This is between Norway and Greenland, just north of Great Britain.
They caused a very large tsunami in the North Atlantic Ocean. About 290 km length of coastal shelf, 3,500 km3 of debris fell. This is an area the size of Iceland covered to a depth of 34 m (112 ft).
Based on carbon dating of plant material, the latest incident occurred around 6100 BC. 
In Scotland, traces of this tsunami have been found in the Montrose Basin (estuary of the South Esk river), and the Firth of Forth, up to 80 km inland and 4 metres above today's normal tide levels.
For 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 it would only happen again after a new ice age. This conclusion is supported by scientific studies. Facts and arguments supporting this conclusion were made public in 2004.
It was decided that the development of the Ormen Lange gas field would not significantly increase the risk of triggering a new slide. A new slide would trigger a very large tsunami which would be devastating for the coast areas around the North Sea and the Norwegian Sea.