Spreading is a type of mass movement where a sediment unit is extended and broken up into coherent blocks that are displaced and tilted along a planar slip. High-resolution seafloor data demonstrate that spreading is a common style of submarine mass movement. Submarine spreading is clearly exemplified in the Storegga Slide, Norwegian margin (Fig. 1a, b). The slide occurred 8100±250 cal a BP as a retrogressive slope failure (Haflidason et al. 2005). It is one of the largest known submarine slides and the site of repeated sliding activity. Failures on the Norwegian margin are linked strongly to the growth and retreat of the Fennoscandian ice sheets, in particular to the alternating deposition of glacigenic debrites and basal and deformation tills during glacial maxima (e.g. O1–O2 30–15 ka and O4–O7 200–130 ka sub-units of the Naust Formation), and of fine-grained glacimarine, hemipelagic and contouritic sediments during interglacials (e.g. O3 130–30 ka sub-unit of the Naust Formation). The Naust sub-units are described in full in Berg et al. (2005). Differences in the geotechnical properties of these sediments, coupled with seismicity, rapid sediment deposition, associated high pore pressures and the regional topography and structural setting, are responsible for >20 slope failures across the region during the Quaternary (Solheim et al. 2005).
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