Abstract

The U.S. Navy nuclear research submarine NR-1 was used to investigate the Storegga Slide (Norwegian Sea) shelf break, headwall, and upper debris-flow fields to a maximum water depth of 630 m (2070 ft). About 275 km (170 mi) of seafloor was traversed in 1 week, collecting 150-kHz side-scan sonar, current speed and direction, bathymetry, optic imagery, and visual observations. Side-scan imagery was used to identify four provinces, some corresponding to distinct optic-scale characteristics. We found the Storegga outer shelf streaked and locally incised by iceberg plow marks or otherwise “lineated” in the side-scan imagery. We attribute the “streaking” to the strong Norwegian-Atlantic Current and perhaps the Norwegian Coastal Current. Despite our short current-sampling “snapshot,” we found good agreement between measured current directions and current-generated seafloor features. Along the headwall, just seaward of the iceberg plow marks, are deep-water, coral (Lophelia pertusa) reefs. Recent instability (post-8.15 ka) along part of the headwall region is indicated by cobble/boulder fields devoid of sessile biota (such as sponges). No obvious fluid expulsion or extensional features were discovered in the small portion of the Storegga Slide that was investigated.

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