The Storegga Slide and Tsunami in the North Atlantic Region
by
Alastair Dawson
Coventry University, UK
Coauthors: Sue Dawson, David Smith (Coventry University, UK), Stein Bondevik (University of Tromso, Norway), Jon-Inge Svendsen, Jan Mangerud (University of Bergen, Norway), Petter Bryn (Norsk Hydro, Norway), Carl Harbitz, Bjorn Gjevik and Geier Pedersen (University of Oslo), David Long (British Geological Survey, Edinburgh, UK), Shaozhong Shi (Liverpool Hope University, UK)

One of the world's largest submarine slides with a total volume of ca. 5,600 km3 occurs on the continental slope west of Norway. Part of the sediment complex, with a volume of ca. 1700 km3 is generally believed to have moved as an underwater slide approximately 7200-7300 radiocarbon years ago. The scale of the slide deposit is demonstrated, for example, by a scarp slope 150km in width that defines the head of the slide and by individual blocks of Quaternary sediment up to 200m in length that are incorporated within the slide complex. The sudden movement of sediment across the Norwegian continental slope and onto the abyssal plain of the Norwegian Sea is believed to have generated a large tsunami that was propagated across the North Atlantic and Norwegian Sea regions. Deposits attributable to this tsunami have been discovered at numerous coastal locations in western Norway, Scotland, Faeroe Isles and as far south as eastern England. Modelling of the slide and tsunami appear to indicate that it had an average velocity of ca. 35m/s and it is estimated that the majority of the sediment mass was moved during approximately 2 days. Modelling of the tsunami runup at the coast would appear to suggest that at certain locations in western Norway, the generation of the tsunami was associated with an initial drawdown (lowering) of sea level at the coast in the order of -8m and that this was quickly followed by a sea surface rise in the order of +16m. Geological studies of coastal deposits in Scotland and Norway attributable to the tsunami indicate that the tsunami runup exhibits strong local and regional variability that was strongly influenced by coastal configuration and the effects of wave resonance within individual bays and estuaries. In parts of the Shetland Isles, the runup at the coast may have been as much as between +25/+30m above sea level. It is not known if the slide was generated by a large offshore earthquake or by gas release from within the slide sediments.

Date received: April 30, 2002