Link to USGS home page
Sound Waves Monthly Newsletter - Coastal Science and Research News from Across the USGS
Home || Sections: Spotlight on Sandy | Fieldwork | Research | Outreach | Meetings | Awards | Staff & Center News | Publications || Archives

 
Outreach

San Francisco Bay Floor Explored in Public Lecture


in this issue:
 previous story | next story

Cover photo from USGS Circular 1259.
Above: Cover photo from USGS Circular 1259, "Shifting Shoals and Shattered Rocks…." This panoramic view from the Marin Headlands shows a large container vessel passing beneath the Golden Gate Bridge and entering west-central San Francisco Bay. Photograph by Mike Diggles, USGS. [larger version]

A public lecture on "Shifting Shoals and Shattered Rocks—How Man Has Changed the Floor of San Francisco Bay" drew more than 100 people to the U.S. Geological Survey (USGS) campus in Menlo Park, Calif., on the evening of November 17, 2005. The audience sat spellbound as geologists John Chin and Florence Wong of the USGS Western Coastal and Marine Geology Team (WCMG) related historical events that have affected the bay and described mapping techniques that let us view its floor in unprecedented ways.

John began the lecture with a short history of human influences on the bay. He showed striking photographs of hydraulic mining washing away whole hillsides in the foothills of the Sierra Nevada during the 19th-century California Gold Rush; before this practice was banned in 1884, it sent enormous volumes of sediment down the rivers and into San Francisco Bay, reducing the water depth over large areas. He identified bedrock knobs on the west-central bay floor that have been repeatedly blasted to accommodate increasingly larger vessels, and showed photographs of blasting in the early 1900s. He explained how San Francisco's Marina District, once sand dunes, was transformed into the site of the 1915 Panama-Pacific Exposition (only the Palace of Fine Arts remains from this era), and how Treasure Island was created from dredged sand for the 1939 Golden Gate Exposition.

Blasting of Arch Rock in 1901. Hydraulic mining at the Malakoff Diggings in the foothills of the Sierra Nevada.
Above Left: Blasting of Arch Rock in 1901. View from San Francisco. Alcatraz Island is in the right middle ground. Photograph courtesy of U.S. Army Corps of Engineers. [larger version]

Above Right: Hydraulic mining at the Malakoff Diggings in the foothills of the Sierra Nevada. Photograph by Carleton E. Watkins, courtesy of the Bancroft Library, University of California, Berkeley. [larger version]

Lefthand image is part of a navigational chart published in 1883. Center image is the same chart overlaid with soundings collected by the National Oceanic and Atmospheric Administration in the 1990s. Right-hand image is the same area mapped by multibeam swath sonar in 1997.
Above: Increasing data density has led to increasingly detailed bay-floor maps. Lefthand image is part of a navigational chart published in 1883; each number represents one sounding (depth reported in fathoms). Center image is the same chart overlaid with soundings (blue dots) collected by the National Oceanic and Atmospheric Administration (NOAA) in the 1990s. Right-hand image is the same area mapped by multibeam swath sonar in 1997. Red rectangle in the center image contains 1 sounding; the same area (yellow rectangle) in the right-hand image contains 48 soundings. [larger version]

John also described multibeam swath-sonar mapping, a fairly recent technology that has enabled scientists to study the San Francisco Bay floor in more detail than ever before. In contrast to single-point soundings that were the norm through the early 1900s, and lines of soundings that were collected from World War II into the 1990s, multibeam mapping allows scientists to map virtually 100 percent of the sea-floor surface, producing photograph-like views of the sea floor. In her section of the lecture, Florence Wong explained how geographic-information-system (GIS) techniques allow scientists to reconfigure multibeam and other mapping data for numerous purposes—from detecting and quantifying past changes, such as alteration of land by urbanization, to making models and predictions about the future, such as the likely intensities of earthquake shaking in different areas. She showed how multibeam data collected by the USGS in San Francisco Bay had been used to calculate how much rock must be removed from a bedrock knob to eliminate its threat to deep-draft vessels, and to reconstruct how disposal of dredged material transformed a deep depression off Alcatraz Island into a large mound (contradicting expectations that tidal currents would sweep away the disposed material).

Computer-Generated "Flythrough"
still image from computer-generated flythrough High-density multibeam swath-sonar data produce photograph-like views of underwater terrain, as shown in this frame from a computer-generated "flythrough" created by Peter Dartnell from USGS data collected in 1997.

Watch the "flythrough" (8.9 MB MPEG)

NOTE - QuickTime(TM) Required: You will need to have the the free QuickTime(TM) Player installed on your computer to watch the video.

Florence closed the lecture with a computer-generated "flythrough" of the central bay floor, created from multibeam-mapping data by Peter Dartnell, also of WCMG. This virtual tour, in which the viewer skims past Alcatraz Island, around Angel Island, over large sandwaves, deep depressions, and bedrock knobs, and out to the brink of the Golden Gate, drew so many oohs and ahhs from the crowd that it was played twice. The lecture was based on a USGS Circular that John and Florence coauthored with Paul Carlson, now a WCMG emeritus scientist. Circular 1259 is posted online at URL http://pubs.usgs.gov/circ/2004/c1259/.


Related Web Sites
Shifting Shoals and Shattered Rocks—How Man Has Transformed the Floor of West-Central San Francisco Bay - U.S. Geological Survey Circular 1259
U.S. Geological Survey (USGS)

in this issue:
 previous story | next story

 

Mailing List:


print this issue print this issue

in this issue: Fieldwork
cover story:
USGS Scientists Investigate New Orleans Levees

special feature:
Post-Katrina Cleanup—a Volunteer's Reflections

Offshore Impacts of Hurricane Katrina

Sediment-Toxicity Studies in Western Long Island Sound

Sea-Floor Geology Off Massachusetts Coast

Alvin Dives to Deep-Water Coral Habitats

Research Study Links Urbanization to Amphibian Decline

Outreach San Francisco Bay Floor Explored

Briefing on Coastal Research in Hawai'i

USGS Research on the Kona Coast, Hawai'i

Meetings Third International Symposium on Deep-Sea Corals

Awards Award for USGS Map Hawaii's Volcanoes Revealed

Staff USGS Citizen Soldier on the Move!

Native-Plant Landscaping in Florida

Publications New Book on Benthic Habitats and the Effects of Fishing

Dec. 2005 / Jan. 2006 Publications List


FirstGov.gov U. S. Department of the Interior | U.S. Geological Survey
Sound Waves Monthly Newsletter

email Feedback | USGS privacy statement | Disclaimer | Accessibility

This page is http://soundwaves.usgs.gov/2006/01/outreach.html
Updated April 15, 2014 @ 01:53 PM (JSS)