A Census Study of Submarine Canyons in the Eastern Pacific

**Statement of Problem**: More than 30 years ago Francis Shepard lead a
nine-year expedition that collected approximately 200 current meter
records in the axis of more than 20 submarine canyons (Shepard et al.,
1979). These pioneer data provided the impetus for submarine canyon
research all over the world. These studies were technologically limited
by their primitive (although state-of-the-art at the time)
instrumentation. Specifically, the data lacked the length of
observation, resolution, and vertical depth range of instrumentation
that are necessary to categorize and quantify the hydrodynamics and
transport (of particles, including sediment and contaminants) in
submarine canyons. We propose a new project to collect field data in
known active submarine canyons with state-of-the-art equipment and much
improved temporal and spatial coverage to update and greatly improve our
understanding of submarine canyon processes. We also propose to collect
geophysical data and maps of the studied canyons. The geophysical data
and the advanced oceanographic data will help us to interpret the
hydrodynamics, transport, and the evolutions of the submarine canyons.

**Objectives**: The main objectives are:

-   To collect oceanographic data for the much-needed update to
    Shepard's pioneer studies of submarine canyons.

-   To collect concurrent geophysical data of the canyons studied.

-   To integrate and interpret both the legacy and new data to better
    understand oceanographic and geological processes (frequency and
    size of turbidity currents, cross-margin particle transport,
    response and relation to sea level rise); to identify geological
    hazards and/or beneficial use of the canyons (sand resources, sewage
    discharges, dredge dumps etc.); and to build a baseline for future
    studies of canyon evolution.

**Work Strategy**: In this multi-year project, USGS and partners will
first decide on a prioritized list of canyons to be studied based on
scientific importance, societal relevance, fund availability, and
logistic practicality. The geophysical (high-resolution swath
bathymetry, sub-bottom profiles) and oceanographic (moorings) data may
be collected concurrently, but the oceanographic moorings will require
at least 6 -- 9 months deployment for seasonal coverage.

**Relevance and Impact**: Active submarine canyons extend across
continental shelves and generally head in the nearshore zone where there
is active sediment transport in littoral cells or where the canyon is
fed directly by a river. These canyons form preferential (an order of
magnitude difference comparing with non-canyon transfer) conduits for
cross-margin transfer of sediment, pollutants, e.g., DDT residues, as
well as carbon and other ecosystem-relevant elements. In addition, the
canyons pose potential geological hazards because submarine landslide
commonly occurs on the steep canyon walls and could potentially generate
tsunamis and/or turbidity currents. Data from this proposed project
would aid decision-making on how some canyons can be utilized to benefit
the coastal societies (e.g., institute sand bypassing to replenish
beaches) and/or to mitigate the adverse impact by inevitable human
activities such as dumps for dredging spoils or sewage outfall
discharges into submarine canyons. Moreover, the improved understanding
of processes operating in canyons and Shepard's baseline observations
could stimulate discussions over the relationship between climate change
and canyon circulation.

**Partnerships**: NOAA, CSUMB, MBARI, NPS

**Contact**: Jingping Xu (<jpx@usgs.gov>) and William Normark
(<wnormark@usgs.gov>), USGS Coastal and Marine Geology Team, Menlo Park,
CA

# References

Shepard, F.P., et al., 1979. Currents in Submarine Canyons and Other
Seavalleys. AAPG Studies in Geology No.8,