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Slide Dangers Remain, Study Finds

Federal analysis cites threat to La Conchita. But not all residents are convinced that the entire town is imperiled.

February 19, 2005|Daryl Kelley | Times Staff Writer

Following intense rain, more landslides will probably occur at La Conchita, the seaside Ventura County hamlet where 10 people were killed last month when a wave of mud and debris crushed their homes, a new federal study has found.

"Future landslides are inevitable there," said research geologist Randy Jibson, author of a U.S. Geological Survey analysis begun after the Jan. 10 tragedy and released Friday.

"I call La Conchita heaven as a landslide scientist," he said. "But it's landslide hell as a human being."

Citing historical accounts of landslides dating back to 1865, including another huge slide 10 years ago, Jibson said La Conchita's remaining 161 houses are in one of the most slide-prone areas in the nation and are not safe places to live.

Nine houses were destroyed in the March 1995 slide, and 12 more last month.

"I'm not saying there's a landslide perched there that's going to wipe out the community," Jibson said.

"But there's the potential on many different parts of that bluff for a landslide that could reach any part of that community," he said.

Without another monster storm this winter, like the record-setting rainfall in January, La Conchita will probably weather this winter without another large slide, Jibson said.

But if there were another major storm, the probability of a slide goes up dramatically, he said.

Not all La Conchita residents are convinced that the entire town is imperiled, said Mike Bell, an unofficial community spokesman.

And despite offers of federal relocation loans, some homeowners say they can't afford to leave because they're stuck with huge mortgages.

"Inevitable?" Bell said of another slide. "Absolutely, in geological time, but not in my lifetime."

Bell said that most of the small community -- wedged between a 500-foot bluff and U.S. Highway 101 -- is north of the 1995 slide and wasn't physically damaged.

"In the 10 years since the original slide, nothing has come down north of it," Bell said. "There are eight or nine streets north of it and just three or four directly below it."

Jibson said that no part of the community should be considered out of danger.

"There are a number of small landslides north of the big slide," he said.

"And the potential for slides in that area is very significant. I don't think there's anywhere on that slope that's free from landslide hazard."

Jibson's new study reinforces the findings of a string of geologists who have documented a series of slides at La Conchita since the Rincon coast was settled in 1850.

That coastline, which twists 15 miles between Ventura and Carpinteria, is unstable because it is composed of soil that was once a sandy sea bottom, they found.

It still rises at a geologically torrid pace of 5 yards every thousand years, while faults allow for rapid erosion by rainfall.

The result is a series of ravines with steep sides that collapse easily when saturated by rains.

Jibson said La Conchita, which sits on a major earthquake fault, is also subject to landslides during temblors.

After the 1994 Northridge quake, Jibson said scientists detected 11,000 landslides, most along ridgelines in the mountains near Santa Paula and Fillmore, which are composed of the same type of sandy soil as the bluff at La Conchita.

"That formation goes straight east from La Conchita," he said. "It's a shallow marine sediment, and it's very weak."

Jibson's study found that the January landslide was an offshoot of the 1995 slide.

"About 15% of the '95 slide took off in January," producing about 450,000 tons of soil and debris that rushed like water down the hillside.

"It all took about 10 or 20 seconds," he said. That was very different from what occurred in 1995, when heavy rains in January saturated the area, but the slide didn't occur until March.

Even then the mountain descended almost gradually, taking about 10 minutes to slide and giving people time to rush to safety.

No one was injured.

"My greatest concern," Jibson said, "is that the rest of the '95 slide is going to mobilize, like what happened last month, and quickly push further into the neighborhood."

Some residents are taking the threat seriously. Roger Hart, who stayed after the '95 slide because the debris didn't come close to his home, has abandoned it now.

"I won't ever spend another night in La Conchita again," he said.

"Before I stayed there because I was in denial. Well, I'm not in denial anymore."

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Times staff writer Catherine Saillant contributed to this report.

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