Axial Channels of Submarine Canyons off California
C. K. Paull, D. Caress, W. Ussler, III, E. Lundsten, and H. Thomas
Monterey Bay Aquarium Research Institution, Moss Landing, CA, [email protected], [email protected], [email protected], [email protected], [email protected]
Ultrahigh-resolution surveys have recently been conducted that outline topography within the axial channels of eight 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 and a nearly horizontal or slightly up-canyon slope on the up-canyon side. These bedforms have 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, which suggest that these canyons are active. In contrast, the submarine canyons with heads on the outer shelf (Soquel, Santa Monica, and San Mateo) 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, which suggest that they are inactive. Apparently wave-like bedforms are a common characteristic of active submarine canyons.
AAPG Search and Discovery Article #90088©2009 Pacific Section Meeting, Ventura, California, May 3-5, 2009