2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 9
Presentation Time: 10:15 AM

Topography within the Axial Channel of Seven Submarine Canyons off California

PAULL, Charles1, CARESS, David1, USSLER III, William1, LUNDSTEN, Eve1, THOMAS, Hans2 and ROCK, Steve1, (1)Monterey Bay Aquarium Research Institution, Moss Landing, CA 95039, (2)Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA 95039, paull@mbari.org

Ultrahigh resolution surveys have recently been conducted that outline topography within the axial channels of seven submarine canyons off California. Multibeam bathymetry (vertical precision of 0.15 m and horizontal resolution of 1.0 m at 50 m survey altitude) and chirp seismic-reflection profiles (vertical resolution of 0.11 m) were collected from an autonomous underwater vehicle (AUV). An inertial navigation system combined with a Doppler velocity sonar allows the AUV to fly through the sinuous canyons at 3 knots on a pre-programmed route while maintaining an ~50 m altitude over bottom.

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.