The Storegga Slide: A Major Challenge on the Northeast Atlantic Margin
Espen Sletten Andersen1, Anders Solheim2, Petter Bryn1, Carl Fredrik Forsberg3,
Kjell Berg4, and Tore Kvalstad3
1 Norsk Hydro ASA, Oslo, Norway
2 International Centre for Geohazards, Oslo, Norway
3 Norwegian Geotechnical Institute, Oslo, Norway
4 Pertra AS, Trondheim, Norway
The Ormen Lange gas field, which is the second largest gas field offshore Norway, was discovered in 1997. The field is located in water depths of 850 to 1100 m, in the central scar left after the Storegga Slide. This submarine slide occurred about 8200 years ago and is one of the greatest submarine slides ever recorded. Run-out is nearly 800km into the Norwegian Sea, and the volume of mobilized sediments is roughly 3000 km3. The affected area is 90 000km2, equivalent to nearly 30% of the Norwegian mainland, and the slide caused a devastating tsunami. The Storegga Slide is only the last in a series of huge slides in the same region during the last 0.5-1.0 My.
Extensive multidisciplinary geohazard studies have been carried out since the discovery of the field, including morphology, geophysics, regional and local geology, geotechnical borings, slope stability assessments, numerical modelling, gas hydrate studies, etc. The studies have revealed a close relationship between the variable glacial – interglacial depositional regimes and large-scale sliding. Long periods of contouritic, fine-grained deposition in an interglacial to interstadial regime, are interrupted by short periods of intense, rapid glacial deposition during peak glaciation. This caused excess pore pressure to build up in the buried deposits, reducing stability. The slide was triggered on the mid-lower slope and developed retrogressively.
The studies were performed in a fruitful cooperation between industry and academia, and showed that such an integrated, multidisciplinary approach was the key to success. Despite challenging morphological and geotechnical conditions, the Ormen Lange area is considered safe with regards to new large slides. The Norwegian Parliament approved development of the Ormen Lange gas field in 2004. This presentation emphasises on the slide morphology, the deposits and the geohazard aspects of the region.