15 December 2000
American Geophysical Union Fall Meeting
Media Contact: Debbie Meyer, AGU press room, Dec. 15-19, (415) 905-1007 or at MBARI
(831) 775-1807, firstname.lastname@example.org
Researchers report on submarine
landslide hazards off Santa Barbara, California
SAN FRANCISCO, California—Using high-resolution bathymetric data and remotely operated vehicles, geologists at the Monterey Bay Aquarium Research Institute (MBARI) have uncovered new evidence of extensive underwater landslides off the coast of Santa Barbara, California. These data have produced one of the clearest images of a submarine landslide ever obtained.
Boxed area (enlarged right) shows a large submarine landslide off Santa Barbara, California.
Detailed view of this complex, compound landslide.
MBARI scientist Gary Greene will summarize results of these studies at the American Geophysical Union meeting in San Francisco during the press briefing "Predicting submarine mass failures and tsunami hazards" (Monday, December 18 at 11:00 AM). These observations are helping scientists who study tsunami hazards to determine the causes and geographical extent of potential tsunami-producing landslides in southern California.
This research began in 1998 when MBARI conducted a high-resolution bathymetric survey of the Santa Barbara Basin seafloor. The resulting maps revealed features that Greene and his colleagues interpreted as submarine landslides along the northern flank of the basin. They mapped in detail a large, 130 km2 slump off Coal Oil Point near Goleta. This prominent slump is 14.6 kilometers long by 10.5 kilometers wide and extends from 90 meters to a depth of 570 meters.
"We were surprised to see the extent and complexity of apparent mass seafloor wasting in the Santa Barbara Basin," said Greene. "This slide evidently moved in three different events. Each event displaced enough sediment to be capable of generating a tsunami, if the displacements occurred rapidly."
What triggered these underwater slides? To address this question, Greene and his colleagues used ROV Ventana in October 1998 to collect seafloor samples and video. They were particularly interested in testing the role of fluids in weakening the sediments and stimulating the landslides. Sediment push cores were taken in three areas of the Goleta slide (upper, middle, and lower). The ROV also recovered samples of carbonates in the upper, or headscarp, area. The carbonates were suggestive of fluid seepage in the past, but the researchers found no direct evidence of venting fluids. They returned to the Goleta slide headscarp with ROV Tiburon in May 2000. Additional sampling in this area did not uncover evidence of fluid venting. However, push cores from dives on smaller slides to the west and east contained some bacterial mats— organisms that are indicators of seepage.
Dating submarine slides continues to be a challenge for geologists and this study was no exception. Greene and his colleagues were unable to find conclusive evidence for dating the slide. Their observations have contributed to the growing information about submarine canyons but there are still many unanswered questions that require additional study. Better understanding of the timing and mechanisms involved in submarine landslides may help scientists assess future landslide potential in other areas.
Press briefing, Monday 11:00, MC 112
Predicting submarine mass failure and tsunami hazards
OS21H-10, Tuesday 11:15, MC 122
Greene, Maher, and Paull. Landslide hazards of off Santa Barbara, California