Topography within the Axial Channel of Seven Submarine Canyons off California
The submarine canyons that head near the shoreline (Monterey, Hueneme, Mugu, Redondo and La Jolla) all contain similar wave-like bedforms with wavelengths of 20 to 100 m and amplitudes of up to 2.5 m oriented roughly perpendicular to the channel axis. These bedforms are asymmetric with a steep face on the down-canyon side while the other face is nearly horizontal or dips up-canyon, and form crescent-shaped crests oriented concave down-canyon. They are observed to occur throughout the surveys (from ~80 to ~800 m water depths) and appear to be grouped into genetically similar packages 0.1 to 3 km long that terminate upslope at a somewhat higher topographic step. Generally, the bedform groups are contained within the axial channel, but some wave-like bedforms extend up the sidewalls of the canyon. ROV-collected vibracores show that near-seafloor sediments associated with the bedforms are composed of recent coarse-grained gravity flow deposits, suggesting these canyons are active. In contrast, the two submarine canyons with heads on the outer shelf (Soquel and Santa Monica) lack these bedforms and have relatively smooth axial channel floors. ROV-collected vibracores show that these canyons are filled with generally uniform fine-grained deposits, suggesting they are inactive. Apparently wave-like bedforms are a common characteristic of active submarine canyons.