The Storegga tsunami along the Norwegian coast, its age and runup

The statigraphy in 25 coastal lakes shows that most of the Norwegian coastline was impacted by a large tsunami about 7200 C-14 BP. The methodology has been to core a staircase of lake basins above the contemporary sea level in several areas and to map the tsunami deposit to its maximum elevation. The tsunami was identified in the sedimentary record as an erosional unconformity overlain by graded or massive sand with shell fragments, followed by redeposited organic detritus. The greatest recorded runup along the coast (10-11 m above high tide) is found in areas most proximal to the Storegga slide scar on the Norwegian continental slope (Sunnmore). To the north and south, runup is less, about 6-7 m at Bjugn (250 km north of Sunnmore) and about 3-5 m in Austrheim (200 km to the south of Sunnmore). This runup pattern supports the suggestion that the tsunami was generated by the Second Storegga Slide. The recorded runup heights are consistent within and between the investigated areas, and imply that the tsunami wave was not significantly influenced by the local topography, suggesting a very long wave length. The mapped runup estimates are in good agreement with a numerical model of the tsunami generated by the Second Storegga slide, and indicate that the slide was a single major event rather than a set of smaller slides.