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One of the World’s largest known submarine slides is found in the Storegga area off the coast of Mid-Norway. The slide area has been investigated by seismic profiling, seabed sampling and long-range (Gloria) and medium-range side-scan sonars. The 290 km long headwall is located at the shelf edge 100 km off the coast. The slide extends down the continental slope and into the abyssal plain to a distance of more than 800 km. The maximum thickness is 450 m and a total of about 5600 km 3 of sediment was involved in the sliding. Three main slide events are distinguished. The First Storegga Slide was the largest (about 3880 km 3 ) and probably was formed 30000—50000 years BP. The two other events seem to have occurred in near succession about 6000—8000 years BP. The Second Slide, which consisted of more consolidated sediments than the First Slide, cut back 6-8 km headwards beyond the First Slide and removed some 450 km 2 of the continental shelf edge. It involved large blocks (olistoliths) of sediments that can be recognized in hummocky slide deposits both within the slide scar and on the abyssal plain. Two huge sediment slabs, 150—200 m thick and up to 10 x 30 km wide, were transported about 200 km down an average slope 0.3°. The Third Storegga Slide was limited to the upper part of the Second Slide scar, and probably occurred as a final, somewhat delayed stage of the Second Slide. In the deepest part of the Norway Basin, more than 750 km from the headwall, a thick (more than 6 m) fine-grained turbidite is related to the Second Storegga Slide. Several other turbidites are found in cores from within the slide scar and on the inner part of the abyssal plain. We believe that earthquake loading and decomposition of gas hydrates caused liquefaction of the sediments and thus triggered the slides.

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About 3 million years ago, major ice sheets developed over Scandinavia and began to deliver large volumes of sediment to the mid-Norwegian shelf. The shelf was built out in a prograding pattern towards the west, and more than 1000 m of sediments was deposited over large areas on the middle/outer shelf. The dominating large-scale depositional pattern is a series of prograding wedges and flat-lying, sheet-like units mainly of glacial origin. On top of these units are flat-lying till units deposited during the last few glaciations, commonly separated from the underlying units by one or several erosional unconformities. The lithology of these layers is generally fine-grained, mainly clay and silt, but with sporadic clasts up to boulder size. Based on regional and detailed bathymetry, the ice-flow pattern from the last glaciation has been reconstructed on the shelf. This involved a very dynamic ice sheet with fast-flowing ice streams in the transverse, cross-shelf troughs, separated by more passive ice domes on the intermediate shallow banks. The ice streams appear to follow the cross-shelf troughs from glaciation to glaciation, but occasionally they switched to new flow paths. The thick Quaternary sediments on the outer part of the mid-Norwegian shelf represent a challenge for hydrocarbon exploration. Several large slides have occurred from the shelf break and down the continental slope. During the last few years there has been an increased focus on investigating the Quaternary succession in order to search for hydrocarbon prospects. The potential for finding reservoirs in these sediments is discussed, and a few examples of gas discoveries are shown. The Peon gas field (c. 250 km2) is located in the glacially eroded Norwegian Channel above the Upper Regional Unconformity (URU) separating flat-lying glaciogenic sediments from dipping sedimentary units. The reservoir is developed in glaciofluvial sands a few hundred thousand years old, and sealed by flat-lying glaciomarine sediments and till units.