Geology of the Gulf of the Farallones National Marine Sanctuary

Summary

"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 deposi...