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Coastal and Marine Geology Program > Geology of the Gulf of the Farallones National Marine Sanctuary

Geology of the Gulf of the Farallones National Marine Sanctuary

USGS Fact Sheet

Dr. Herman Karl and colleagues.
Dr. Herman Karl and colleagues. [larger version]
"The geology and oceanography of the Farallones and surrounding area is atypical and complex. These factors complicate the process of understanding the environmental effects of man's influence such as the disposal of dredge spoils and radioactive wastes. Our goal is to assemble, in a non-crisis mode, geological information to support sound management decisions for any purpose."

- Dr. Herman Karl, U.S. Geological Survey

Considerable public attention has focused on the environmental stress in and around the Gulf of the Farallones National Marine Sanctuary (NMS).

The U.S. Geological Survey (USGS) provides geological information in support of studies related to proposed siting of offshore areas for disposal of dredge spoils and to determining locations of barrels of radioactive waste. The potential for damage to the marine environment from disposal of dredge materials and from rupture of waste containers is difficult to assess without a detailed knowledge of geology, oceanography, and the movement and ultimate fate of transported sediments.

USGS studies perform a critical role in the preliminary study of potential disposal sites for dredge materials.

Cooperative work since 1990 with the Environmental Protection Agency (EPA), the Army Corps of Engineers, and the U.S. Navy has reduced the number of candidate disposal sites from six to three in an approximate 1,000 square mile area west of San Francisco. Sidescan sonar surveys were conducted in all areas in cooperation with the private sector and geological interpretations were derived from these images in preparation for site-specific studies conducted by EPA. A key set of geological characteristics for a proposed dredge-materials disposal site, among other logistical attributes, includes a featureless plain with gentle slopes, no evidence of mass movement of sediments or rock, a lack of strong currents that might redisperse dredge materials, and low-level biota. The ideal site would be geologically stable with net deposition rather than erosion or sediment instability.

Shaded relief map of onshore and offshore areas in the San Francisco-San Jose, California region.
Shaded relief map of onshore and offshore areas in the San Francisco-San Jose, California region showing the Farallon Islands National Marine Sanctuary (green outline). Areas of special environmental concern include three of the six EPA candidate site (yellow outline) for disposal if dredge spoils from San Francisco Bay, and the large areal extent of dumping toxic waste barrels (red outline). Note the three sites (stars) that are designated radwaste disposal sites. [larger version]

The role of USGS scientists is simply to interpret the geological and geophysical data for regulatory agencies. USGS does not make judgments about the suitability of an area as a disposal site. Officials responsible for enforcing environmental regulations use these geologic interpretations along with other criteria to select appropriate disposal sites.

USGS scientists have mapped a small portion of the area known to contain hazardous wastes, and have made significant advances in interpreting sonar signals attributed to the containers.

Digitally-enhanced images used to disringuish sonic returns. Barrel of radioactive waste.
Digitally-enhanced images used to distinguish sonic returns. Top - A double blip characterizes the return from a 55-gallon oil drum. Bottom - Tightly-gathered multiple returns are characteristic of a cluster of barrels that were originally strapped together before being dumped overboard. [larger version] Barrel of radioactive waste on the steep continental slope at a depth below sea level of about 2,000 feet (610 meters). Photo courtesy of R. Dryer, U.S. Environmental Protection Agency. [larger version]

Between 1946 and 1970, nearly 50,000 drums of hazardous and radioactive wastes were dumped over a 350 square nautical mile area that overlaps the Farallones NMS. The task facing environmental managers is to assess contamination of the environment around the 55-gallon drums. However, managers do not know the precise locations of these containers and therefore cannot put together an effective sediment and water sampling program that will provide clues to the extent of contamination, if any. USGS mapping, in cooperation with the National Oceanic and Atmospheric Administration (NOAA), to date covers just 15 percent of the potentially contaminated area. USGS scientists have determined that the sonar backscatter signal can be digitally enhanced to distinguish non-geologic targets such as waste containers, from geologic targets.

USGS scientists understanding of the geology in the marine environment is a key to selecting appropriate mapping technology.

Broad-beam sonar scanning used for reconnaissance mapping of the Exclusive Economic Zone (EEZ) yields insufficient detail. High-resolution scanning yields very fine detail but these surveys take much time and money to complete. USGS researchers use a mid-range frequency for this type of surveying in 3,000 feet of water to resolve features on the seafloor that, with correct interpretation, can lead to a generalized map showing geology as well as other targets of interest. The importance of such USGS maps is realized when the presence and location of specific targets such as hazardous waste containers is sought.

USGS scientists work towards finishing the mapping of the Marine Sanctuary.

Research in cooperation with NOAA and with the private sector continues to produce newer and better means for surveying the seafloor. As the remaining 85 percent of the area is mapped, techniques for resolving seafloor features and for detecting targets of interest are documented for application to other marine environments, such as those offshore from major metropolitan areas or in the vicinity of existing and proposed marine sanctuaries. A library of data combining near- and offshore surveys is available for use in applications requiring geological information.

Contact Information
Dr. Herman Karl
U.S. Geological Survey
345 Middlefield Rd
Menlo Park, CA 94025
Phone: (650) 329-5280
Fax: (650) 329-4710

Related Research Projects:

Gulf of the Farallones Disposal Issues
USGS Coastal & Marine Geology Program

Related Publications:

Beyond the Golden Gate—Oceanography, Geology, Biology, and Environmental Issues in the Gulf of the Farallones - USGS Circular 1198
USGS Coastal & Marine Geology Program

Detection of Barrels that contain Low-level Radioactive Waste in Farallon Island Radioactive Waste Dumpsite Using Side-scan Sonar and Underwater-Optical Systems—Preliminary Interpretation of Barrel Distribution - USGS Open File Report 92-178
USGS Coastal & Marine Geology Program

Current patterns over the shelf and slope adjacent to the Gulf of the Farallones Executive Summary - USGS Open File Report 92-382
USGS Coastal & Marine Geology Program

Map of Seafloor Declivity and Fall Lines on the Continental Slope, Gulf of the Farallones, Central California - USGS Open File Report 93-298
USGS Coastal & Marine Geology Program

Related Links:

Environmental Protection Agency
U.S. Federal Government

U.S. Army Corps of Engineers
U.S. Army

U.S. Navy
U.S. Department of Defense

National Oceanic and Atmospheric Administration
U.S. Department of Commerce

Gulf of the Farallones National Marine Sanctuary
National Oceanographic and Atmospheric Administration

Coastal and Marine Geology Program > Geology of the Gulf of the Farallones National Marine Sanctuary

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