Sidescan and video exploration of the Storegga slide headwall region by submarine NR-1

The U.S. Navy nuclear research submarine NR-1 was utilized in the Norwegian Sea to investigate the Storegga slide shelf break, headwall, upper debris flow fields, and a region north of the headwall. Sidescan imagery was used to identify six provinces, some corresponding to distinct optic-scale characteristics. We found the Storegga outer shelf streaked and locally incised by iceberg plowmarks or otherwise lineated in the sidescan imagery, and sediment waves were mapped north of the slide. We attribute both streaking and sediment waves to the strong NNE-flowing Norwegian-Atlantic Current, and perhaps the north-flowing Norwegian Coastal Current. Despite our short current-sampling “snapshot”, we found good agreement between measured current directions and current-generated seafloor features. North of the slide scar, but collinear with the headwall escarpment, both sidescan sonar and visual observations show abundant pockmarks of various sizes, as well as regularly spaced, shallow linear depressions that are possible indications of sediment porewater or gas escape, extension and incipient failure. However, no obvious vent-related or extensional features were discovered in the small portion of the Storegga slide that was investigated.