Background
Used with permission of EOS
The consequence of a sub-marine land slide, the Storegga tsunami is one of the largest of its type that is known to have ever occurred. The slide and tsunami are believed to have taken place about 8,000 years ago in the Norwegian Sea causing massive waves to run up on the surrounding coasts to elevations as high as 20 meters or 66 feet above sea level (Bondevik et al. 2003).
Soil deposits from coastal areas near the Norwegian and North seas have been studied to determine the age and run up of the tsunami. By examining the sandy soil, and the organic materials trapped within it, geologists have been able to estimate the age of the event with Carbon 14 dating. Dating the layer of sand deposited by the tsunami and the layers of peat immediately above and below proves that the sand is much older than the peat and that the seam of sand was deposited around the year 7,000 BCE (Bondevik et al. 2004).
The wave was generated by a massive sub-marine landslide (approximately 3500 km3 or 840 mi3) that pushed the surrounding ocean waters in the Norwegian Sea in a South/South East direction, with the main front of the wave being felt by the small Shetland Islands off the northern coast of Scotland (Bondevik et al. 2003). Global warming and deglaciation, occurring as the world exited the last major ice age, are believed to have created especially high rates of sediment accumulation on the sea floor in the area where the slide occurred.
This extra sediment, being added at such an accelerated rate, causes greater weight on the soil slopes and excess pore pressures in the soil, which overwhelmed the soil's shear strength and caused the slope to fail, creating the slide (Bondevik et al. 2004). Modern scientists have been able to study the event by looking at the scarring on the sub-marine slope and soil deposits on the surrounding coasts.
