I got this from the San Jose Mercury News website:

Wet winter most likely triggered Laguna landslide, scientists say


Associated Press

LOS ANGELES - Accumulated rainfall from an unusually wet winter most likely triggered Wednesday's landslide that destroyed 18 luxury hillside homes in Orange County's Laguna Beach, scientists say.

Rainwater from the second-wettest season on record in Southern California has been slowly seeping into soil in the Bluebird Canyon area, a process that may have caused saturated slopes to become unstable and eventually slide.

At least four people suffered minor injuries when 18 multimillion-dollars homes tumbled down the hill. Dozens of homes in the neighborhood were in immediate danger and about 1,000 people were evacuated from 350 other homes on the hillside.

Earlier this year, scientists warned that destructive slides would be possible months after the rain stopped and they point to Laguna Beach as a wake-up call for other coastal communities to be on the lookout for any slight earth movement.

"We're not out of the woods yet," said Randall Jibson, a geologist at the U.S. Geological Survey in Golden, Colo.

Houses uphill from the Laguna Beach slide could be in danger of crashing down in the coming days or weeks, landslide experts said.

The hillsides of Bluebird Canyon are made up of weak sandstone rocks and clay sediments that are highly susceptible to landslides. Heavy rainfall in the winter of 1977-78 caused a landslide in the same canyon that destroyed or damaged 50 expensive homes. Most of the houses were rebuilt after the city removed tons of unstable soil.

This year's record rainfall spurred numerous landslides across Southern California, including the deadly La Conchita mudslide that killed 10 people. That shallow, fast-moving mudslide occurred shortly after heavy rain drenched the area, causing massive debris flows that swept away trees and vegetation, leaving huge scars of raw earth on the bluff.

By contrast, the Laguna Beach slide was a slow-moving one that struck nearly a month after the last trace of rainfall. The majority of residents were able to escape after hearing sounds of the earth shifting.

Although scientists cannot predict when the next landslide will occur, property owners in Southern California hillside communities should call in a geologist if they see any visible foundation cracks, tilted telephone poles, buckled streets or other signs of a landslide, said Pam Irvine, a senior engineering geologist at the California Geological Survey.


USGS landslide page: http://landslides.usgs.gov

California Geological Survey: http://www.consrv.ca.gov/cgs/index.htm