USGS Hosts Onshore-Offshore Geologic Map Workshop

By Helen Gibbons and Guy Cochrane July 2007

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Above: USGS scientists use instruments mounted on personal watercraft to conduct bathymetric surveys in shallow areas, such as the surf zone, where water depths can be less than 1 m. Abbreviations: GPS, global positioning system; RTK, real-time kinematics. [larger version]

The U.S. Geological Survey (USGS) and the California Geological Survey (CGS) cohosted a Coastal Map Development Workshop on May 2-3, 2007, in Menlo Park, California, to discuss the content and format of a prototype onshore-offshore geologic map. Typically, onshore geologic and topographic maps are separated from their offshore equivalents not only by an unmapped intertidal zone but also by differences in methods of data acquisition and interpretation. The USGS and the CGS are collaborating with other State and Federal agencies to develop a new type of coastal geologic map that will bridge this gap and serve as an important tool for addressing a broad range of coastal-zone management issues.

The workshop assembled producers and users of coastal maps to discuss the problems and benefits of merging onshore and offshore geospatial data. Attendees from the West Coast, Alaska, the Northeast, and the Gulf States represented numerous organizations, including the USGS, the CGS, the Minerals Management Service, the National Park Service, the National Oceanic and Atmospheric Administration, the U.S. Army Corps of Engineers, many State and local organizations, and private institutions.

Organized by Guy Cochrane of the USGS Western Coastal and Marine Geology Team, the workshop was divided into sessions for presentations and discussions of bathymetry and topography, geology, habitat, and the needs of end users. An extended lunch period allowed people to lay out existing maps and discuss their merits and shortcomings. Participants and other interested persons will also have the opportunity to review the prototype map to be produced for the California Coast State Waters Mapping Project. This map will consist of seamless bathymetry/topography and geology at a scale of 1:24,000 for an area around Santa Barbara, California, where the USGS and California State agencies are already conducting sea-floor mapping and onshore geologic mapping (for example, see Sound Waves article, "Mapping the Sea Floor Off Santa Barbara, California").

A goal of the recent workshop was to develop a plan for maximizing the utility of the prototype map, which will serve as a model for similar maps in other areas. It is expected that onshore-offshore geologic maps will be used by coastal-zone managers and the broad scientific community to address a host of important issues, including coastal erosion and sediment management, sediment and contaminant budgets and transport, onshore and offshore landslides, effects of dam removal, designation of marine protected areas, onshore and offshore infrastructure and development, potential earthquake sources, and potential offshore tsunami sources and tsunami-inundation modeling.

Mapping the Sea Floor Off Santa Barbara, California September 2006

California Coast State Waters Mapping Project State of California

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July 2007

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in this issue:

cover story:
Newly-Discovered Fossil Sponges

Public Lecture: Alchemy in the Abyss

USGS at Florida's Marine Quest

College Students Introduced to USGS Studies

Potential Impacts of Future Sea-Level Rise

Onshore-Offshore Geologic Map Workshop

High-Resolution Map Merges Tampa Bay Bathymetry and Topography

70 Years of Coastal Cliff Retreat in California

July Publications List