More Slope Failures May Lie Ahead

Wednesday’s devastating landslide in Laguna Beach could be just the beginning of a months-long season of falling debris and mud, even though the rains that saturated Southern California last winter are long past, geologists warn.

As a result, local governments are scrambling to prepare for the possibility of damage through the summer and the fall in hilly, slide-prone neighborhoods.

Although rainstorms can cause some unstable hillsides to fail relatively quickly, the worst landslides can occur well after the clouds are gone, said Randall Jibson, a landslide specialist with the U.S. Geological Survey. That’s because it takes weeks for the rain to percolate down through rocks and soil before it collects in enough volume to do real damage.

“We could be looking at a spring or summer or even fall where this sort of thing could pop off all over the Southern California region,” Jibson said. “The rain causes the shallow ones, and then when spring and summer come, that’s when you get the bad ones.”

For example, Jibson said, Wednesday’s slide in Bluebird Canyon in Laguna Beach occurred three months after the bulk of the winter storms passed through the region. An earlier slide there in 1978 took place even later in the year, in October.

Concerned that more slides may be on the way, Glendale has hired an engineering firm to study the sites where slides occurred during winter rains and recommend ways to avoid more damage as water percolates through the Verdugo Hills.

Steve Zurn, the city’s director of public works, said engineers were watching for any slight movements of trees, telephone poles and dirt near slide-prone parts of Camino San Rafael, Cavanaugh Road, Gladys Drive and a nearby service road, as well as several other unstable locations. Except for the Gladys Drive area, where three houses were damaged by winter slides, the other risky portions do not have residential developments.

At the Camino San Rafael site, he said, the earth has been moving steadily since the rainstorms. To avoid future slides, Zurn said, the city plans to remove a significant amount of soil -- from the top of the hill to the bottom.

“I don’t want to go in and repair the obvious damage just to have another failure later,” Zurn said. Storm damage is already estimated to have cost the city $27 million this rainy season, and any additional work could cost millions more, he said.

The city of Los Angeles is monitoring hillsides that its engineers say are prone to landslides, geotechnical engineer Christopher Johnson said in a prepared statement.

“We have geologists in the field on a daily basis,” he said.

Road and utility crews working for Los Angeles County have been instructed to watch for signs that hillsides in unincorporated areas are continuing to move: cracks in streets, tilting trees or telephone poles, muddy drainage.

In particular, county officials have been concerned about homeowners living in areas that were scorched by wildfires in 2002 and 2003, because bare earth left after a fire is more likely to slide during a rainstorm, said county public works spokesman Ken Pellman.

He said his department had notified homeowners in the many hillside areas that had been affected by fire in the county that there was a possibility of landslides and offered tips on how to spot the beginnings of a slide. Additional information is available from the Homeowner’s Guide for Flood, Debris and Erosion Control, on the county’s website, at https://ladpw.org/wmd/HomeOwners/index.cfm.

Pellman also suggested that homeowners check geological maps to see if their property is in a landslide zone and pay attention to moving debris, popping noises and other signs that the hill has become unstable.

If the hill begins to move, leave immediately and call 911, Pellman said. Don’t worry about gathering clothes or keepsakes. “Don’t start packing. It’s better to be safe than dead.”