The Storegga slide: evaluation of triggering sources and slide mechanics

The Storegga slide occurred about 8200 years ago. The enormous slide was released in an area where the average slope inclination is in the order of 0.6-0.7°. Slide mechanisms and possible triggering sources that can cause large scale slide events at such low inclinations have been studied. The morphology of the upper part of the slide scar shows lateral spreads along marine clay layers indicating a retrogressive slide mechanism. Mechanical models of this slide mechanism have been developed considering the stain softening behaviour typical for marine clays. Numerical modelling of the rapid sedimentation during glacial periods and field measurements show that excess pore pressure existed, and still exists in areas adjacent to the slide. The three factors; slide mechanism, excess pore pressure and strain softening, have been incorporated in a retrogressive slide model, which demonstrates that large scale slide processes are possible, even at the low slope gradients in the Storegga area.