Town Given a New Warning

A pair of geologists warned that an earthquake could loosen a bluff over the seaside hamlet of La Conchita, triggering a landslide worse than the one in January that wiped out part of the community and killed 10 people.

Geologists from UC Santa Barbara reported their findings Wednesday at the annual meeting of the Geological Society of America in Salt Lake City. They said a “megaslide” occurred 20,000 to 30,000 years ago and sent tons of mud and rock into the ocean. It is believed to have been one of the largest landslides in the United States, they said.

Researchers Larry Gurrola and Ed Keller are concerned that another giant slide could be in the area’s future, because a major fault bisects Rincon Mountain behind La Conchita.

“That’s the thing that could really get this megaslide moving,” said Gurrola, referring to a possible earthquake. “And if this megaslide reactivates, it could move out a much farther distance, burying the town of La Conchita and Highway 101 under 40 or 50 feet of debris. It makes the threat to residents much greater than previously recognized.”

A powerful storm in January collapsed a cliff overlooking the beachfront town, destroying 12 homes, damaging 11 others and killing 10 people, including several children.

A similar slide in 1995 destroyed nine homes, but no one was hurt that time.

Both scientists said the megaslide broke up the rocks on the cliff, making La Conchita more vulnerable to smaller slides. The cliff also comprises soft shale, which turns into mud during periods of intense rainfall.

The geologists created a computerized digital elevation map of the mountainside behind La Conchita that depicted the telltale semicircle of a giant landslide. The data showed that the rock on the slopes was broken into pieces.

“Once we put the whole picture together, we could say that that entire slope was landslide,” Gurrola said.

Their findings back a report released in February by the U.S. Geological Survey that said a variety of landslide hazards threaten La Conchita. The report found records, dating to 1865, showing that landslides are commonplace and that all 150 homes remaining in the community probably remain vulnerable to another slide.

The western half of the 1995 slide area poses the most immediate danger, geologists said. The eastern half collapsed in January.

The scientists don’t know whether the cliff can be stabilized to provide safe living for residents.

“We just don’t want to see more people killed there, particularly children,” Keller said. “Now we know a lot more about what’s driving the whole thing.”