The Storegga Submarine Landslide - and Tsunami
Wednesday, September 24, 2008 1:37:07 PM
The Storegga Slide was also one of the bigger - or should I say Storegga slides, because sometimes it is seen as a series of slides. The 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 slid into the Norwegian Sea. This collapse involved an estimated 290 km length of coastal shelf, with a total volume of 3,500 km3 of debris (Haflidason et al. (2004) estimated that the minimum volume of sediments displaced was 2400 km3 and the maximum was 3200 km3). The (largest) incident occurred around 6100 BC, that is around 8000 years ago. The mass slid around 800 kilometres into the deep sea, and its back edge is around 300 kilometres long.
Some authors associate the failure of the Storegga Slide with excess pore pressures caused by gas-hydrate dissociation due to sea-level/water-temperature change, other authors consider that the Storegga Slide may have been triggered by offshore earthquakes.
The Storegga submarine landslide occurred indeed (supposedly?) from an area rich in gas hydrates and at about the same time as a large increase in atmospheric methane concentrations recorded in a Greenland ice core. This increase has been hypothesized to reflect methane releases from the Storegga slide debris for several hundred years following the slide. Methane is a powerful greenhouse gas, and methane release from the Storegga submarine landslide may have contributed to the rapid termination of the brief but intense cold event about 8200 years ago and the subsequent evolution of Holocene climate (The Holocene is a geological epoch, which began approximately 10,000 years ago). See: Methane gas release from the Storegga submarine landslide linked to early Holocene climate change: a speculative hypothesis.
The slide speed and the displaced volume were such that they produced a megatsunami. Its consequences are noticeable in Scotland and along the coasts of Iceland, Norway, the Faroe Islands and Shetland. There is evidence that the tsunami reached a height of 25 metres in Shetland. This gigantic tsunami is known as the Storegga Tsunami.
“Record-breaking Height for 8000-Year-Old Tsunami in the North Atlantic” by Bondevik et al.
Eos,Vol. 84, No. 31, 5 August 2003, pp 289–300