In an instant, the rain-drenched hillsides above the La Conchita, CA coastal village came roaring down Jan. 10, killing at least three residents, injuring nearly a dozen and leaving almost two dozen missing.
Video images revealed what appeared to be flowing vegetation as tons of soaked earth, vegetation and debris flowed onto and over 15 homes and a four-block expanse of the community in perhaps the worst, but not the only, landslide that has occurred in California since a series of rain storms began pounding the state two weeks ago.
Heavy rainstorms have been a welcomed relief to drought conditions throughout the state, but they've also revealed the vulnerability of homes dotting the mountainous and hilly regions throughout California.
The U.S. Geological Survey says landslides in the United States occur in all 50 States, but more often in the coastal and mountainous areas of California, Oregon, and Washington, as well as Rocky Mountain states, and mountainous and hilly regions of the East, Alaska and Hawaii.
Peter Yanev, an Orinda, CA-based consulting civil and structural engineer who works in catastrophe management says landslides are most common on hilly and steeply sloped areas, but they can occur wherever there is a slope as shallow as 15 degrees or more.
Landslides can be backyard size or miles long, shallow or deep and they can move a few inches or several miles. They range from soil and mud flows to rock and boulder falls, all of which can take vegetation, structures, vehicles and parts of roadways and other debris along for the ride, according to JCP Geologists of Fremont, CA.
Yanev, also author of "Peace of Mind In Earthquake Country", says landslides are considered a "low probability-high consequence" event and the low probability side of the equation causes people to build and live where they shouldn't.
"It often has nothing to do with how the home was built. Land is cheaper in these areas, but the house should never have been built there in the first place," Yanev says.
On the other side of the equation, the geological event is so potentially disastrous, insurance protection for homeowners is only available through Lloyds of London at a prohibitively expensive $900 to $1,200 annual premium, according to Tully Lehman, a spokesman for the Insurance Information Network of California.
"It may not be available in areas where there have been past land movements and there are unstable soils," said Lehman.
Mudslides or mudflows, a highly liquefied form of landslide, are covered by flood insurance through the federal National Flood Insurance Program. Flood insurance policies, mandated for certain high flood risk areas, but available to anyone who wants to purchase it, costs an average $400 a year, Lehman says.
The high cost of insurance, when it is available, and the potential for disaster associated with living in hilly or mountainous regions, leaves residents shouldering most of the risk.
Civil and geotechnical engineer Allen Kropp of Allen Kropp & Associates, a geotechnical engineering company in Oakland, CA, says residents should be familiar with how near they are to landslide prone areas.
The U.S. Geological Survey, state agencies, including the California Geological Survey and companies like Kropp's offer maps of landslide regions.
"Virtually every city in the San Francisco Bay Area has slides," Kropp said.
Yanev says home buyers or current owners concerned that they are too near a landslide area may want to hire a professional to assess the potential for disaster. That could include a structural engineer to examine the home for signs of landslide activity and a soils engineer to inspect the earth.
"Cracking in the foundation, doors slightly rotated so they jam, both on the downhill side, that's an indication in the instability of the land," said Yanev.
Kropp says most landslides don't occur like the fast-moving La Conchita slide or others which can move as fast as 10 to 20 miles an hour or more, but are more often measured in inches or feet a day -- slow enough to yield warnings.
"The most ominous thing is cracking of the ground in a kind of arcuate fashion, like an arch shaped crack. Most landslides are curved as opposed to liner cracks," said Kropp.
Yanev said, similarly, hillside scalloped shapes with a berm forming at the bottom of the slope is also an indication.
"If you look at hillsides with a big area where there are no oak trees, most likely they slid down the hill. Areas dense with old trees is a good indication of stability," said Yanev.
A report from JCP Geologists says hilly areas left barren of grasses, plants, shrubs and trees, say, by fire, are particularly vulnerable to landslides especially during and after heavy rains. Quakes and construction can trigger landslides, but too much water for the land to hold and the force of gravity is the most common cause.
JCP says geological changes near your home can signal an impending slide. Those changes include new above-ground springs, cracked soil or rocks, bulging slopes, new holes or bare spots on hillsides, tilted trees, muddy waters and excessive ponding.
Only very early landslide prevention efforts are successful at holding back the earth.
"You can protect yourself once a slide starts to move, but it's almost always too cost prohibitive to stop the slide," said Kropp.
Visit the "Victims of La Conchita" website to learn about the outpouring of fundraising efforts, benefits, memorial funds, and other efforts still needed to assist the town's victims.