La Jolla coast rich with sand

San Diego Union Tribune
By Terry Rodgers
April 12, 2007

Scientists from UC San Diego's Scripps Institution of Oceanography have measured and mapped what amounts to a Fort Knox of sand on the seafloor off northern La Jolla.

Scripps Institution of Oceanography Scripps Institution of Oceanography researchers have mapped an enormous repository of seafloor sand off Torrey Pines State Beach. The 12-square-mile area contains an estimated 78.5 million cubic yards of sand, which may become useful as replacement material for eroding beaches.

Much of the sand, which was carried into the area by waves and currents, was trapped by a 20-foot-high ridge that runs along the seafloor. The ridge, created by an uplifted fault line, captured the sand in the same way a snow fence traps snowdrifts. A few of the sand drifts are 65 feet thick.

The sand bank mapped by the researchers could someday be an important “borrow” site for obtaining sand to nourish the region's erosion-plagued beaches, said Rob Rundle, a planner with the San Diego Association of Governments.

In 2001, the association oversaw a project in which 1.5 million cubic yards of sand was dredged from offshore sand drifts and pumped onto beaches from Oceanside to Imperial Beach.

The researchers were able to map the contours of the ocean floor and measure the thickness of the sand by towing a submerged instrument panel with a boat. One of the instruments transmitted acoustic signals capable of penetrating 80 feet of sand.

Geology professor Neal Driscoll, who co-authored a paper describing the project's findings, said researchers also documented “a rich tapestry of rock types” caused by the movement of underwater fault lines.

“These (rock types) really play an important role in what kinds of biological life is going to occur there,” Driscoll said.

For instance, kelp generally grows best where it can attach its roots to a seafloor comprised of rock that is hard and dense.

Anglers will be interested in the underwater ridge identified in the study because it's the type of structure that acts as a fish magnet.

Other scientists who contributed to the study include Leah Hogarth, Jeffrey Babcock, Nicholas Le Dantec, Jennifer Haas, Douglas Inman and Patricia Masters.

The findings were published earlier this month by the Geological Society of America.