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The Holocene Storegga Slide, adjacent to the North Sea Fan, is the most studied of all the Norwegian slides and the subject of ongoing studies (Bugge et al., 1988; Evans et al., 1996; Bryn, P. et al., 2003; Haflidason et al. 2004; Solheim et al., 2005). This was a huge slope failure of Pleistocene sediment, which took place about 8200 years ago (Bryn et al. 2005). Haflidason et al. (2004) estimated that the minimum volume of sediments displaced was 2400 km3 and the maximum was 3200 km3.
The Storegga Slide depression separates the North Sea Fan in the south from the Vøring Plateau to the north. The erosive scar measures some 290 kilometres north to south across the headwall, commonly with 30-50 m height but that can reach 120 m along limited parts of the northern escarpment (Haflidason et al.,2004), and extends at least 225 kilometres north-west from the headwall into the ocean basin. However, the development of the depression and the detailed architecture of the immediately surrounding are results from a large number of palaeoslides that have occurred intermittently since perhaps late Pliocene times (Evans et al., 2005; Nygård et al., 2005). Due to extensive and repeated sediment removal, the volumes of the older slides are difficult to establish, but it seems likely that some were at least as large as the Holocene event (Evans et al., 2005).
Numerous regional models relating to trigger mechanisms and scenarios have been proposed for the Holocene Storegga Slide, many of which would also be applicable to older slides in the area. While 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 (e.g. Mienert et al., 2005), other authors consider that the Storegga Slide may have been triggered by offshore earthquakes (e.g. Atakan & Ojeda, 2005).
Although the mechanism that initiate the Storegga Slide is still not well understood, the first event of the Holocene Storegga Slide, according to Bryn et al.(2002) was followed by successively smaller slides. In some areas sediments have moved as flows, whereas in others they remain as more-or-less coherent blocks. While the slides are generally in tectonic terms, extensional features, numerous zones of compression can be seen where individual flows and slide lobes terminate.
Studies of the sub-surface reveal a large number of palaeoslides with movements that have occurred on a number of different failure surfaces. The present-day absence of non-slide material within the Storegga area indicates that a large-scale present day regional failure in this area is highly unlikely.
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