Geologic Controls on the Distribution of Submarine Landslides along the U.S. Atlantic Continental Margin

Submarine landslides are recognized as an important hazard on continental margins, especially in the generation of tsunamis, and the increased availability of multibeam bathymetry and sidescan sonar imagery along nearly the entirety of the U.S. Atlantic continental slope and rise provides an opportunity to evaluate the controls on their formation and distribution. Landslide distribution is strongly, although not exclusively, controlled by proximity to areas covered by continental glaciers. Landslides cover 33% of the continental slope and rise of the glacially influenced New England margin, 16% of the sea floor offshore of the fluvially dominated Middle Atlantic margin, and 13% of the sea floor south of Cape Hatteras. Quaternary shelf-edge deltas are common on the glacially influenced New England margin, scattered on the Middle Atlantic margin, which is influenced by a few large rivers, and absent south of Cape Hatteras. The headwall scarps of landslides are most common on the lower slope, and the deposits are thin (mostly 20-40 m thick) and comprised primarily of Quaternary material. The largest failures along the margin were sourced on the open slope offshore of the shelf-edge deltas. Two exceptions are large failures south of Cape Hatteras that are sourced on the open slope near salt domes that breach the sea floor. Faults that breach the sea floor and the occurrence of small earthquakes, plus hydrate destabilization along this section of the margin, may have been the triggers for these landslides. Landslides occur on the walls of submarine canyons as well, but the volumes of the deposits from canyon source areas are much smaller than those from open-slope source areas. The distribution of landslides suggests that depositional processes during the Quaternary shaped the shallow stratigraphy and morphology of this margin, and these in turn had a strong control on the stability of the slope.