FOR IMMEDIATE RELEASE
December 5, 2007
Contact: Ed Wilson or Don Drysdale, 323-1886
RAINY WEATHER, FIRE DAMAGE INCREASES RISK OF LANDSLIDES
SACRAMENTO – The California Geological Survey (CGS) today reminded residents to be aware of the potential for landslides and mudslides – especially in areas impacted by recent wildfires. Individuals who live on or below slopes, or in an area where fires have recently burned away plant life, should listen for unusual rumbling sounds and be on the lookout for new cracks in soil, bare hills or downward moving material. A list of additional landslide warning signs is attached.
“Most Californians recognize the potential danger of earthquakes,” said State Geologist Dr. John Parrish, head of CGS. “Although landslides typically aren’t as devastating, they’re much more common. The good news is that landslides, unlike earthquakes, sometimes provide warning signs that, if heeded, can help save lives and property.”
A landslide is any mass of earth and rock that moves downhill by sliding, flowing or falling. Large, slow-moving landslides composed of bedrock can cause extensive property damage, while debris flows, commonly called mudslides, move very quickly.
Landslides can happen at any time but are more likely once the rainy season begins. Areas that have been recently destroyed due to wildfire are particularly vulnerable. Fire damage causes soil to become less absorbent because ash clogs pores in the soil and oil is given off by burning plants, laying down a water-resistant veneer. As a result, rainwater runs off faster instead of sinking into the ground and erosion increases. More than a dozen federal, state and local agencies known as a Multi-Agency Support Group (MASG) are assessing burned areas in Southern California to determine the potential for landslides.
Areas that have experienced landslides in the past are more susceptible to repeat occurrences and regions that received significant amounts of rain last year have an increased potential for a landslide this winter. Exceptionally heavy rain – three or more inches a day or a quarter-inch an hour – also increases the likelihood of a landslide because soil becomes waterlogged.
When California rainfall exceeds normal levels by 150 percent or more, landslides cause, on average, property damage in excess of $100 million and as many as five deaths each year.
“Ultimately, all of us live in California by geologic consent, which is subject to change without notice,” Parrish said. “All we can do is educate ourselves and be prudent in our preparations.”
CGS, part of the California Department of Conservation, provides technical information and advice about landslides and other geologic hazards to the public, local governments, agencies and industries that make land-use decisions in California.
More information about landslides – including tips for residents and mitigation steps – can be found at http://www.consrv.ca.gov/CGS/geologic_hazards/landslides/index.htm.
Tips and Clues That May Save Your Life
Californians who live on or below hillsides, especially in Southern California, should be aware that the upcoming rainy season increases the possibility of landslides. Weak soils/bedrock or ancient landslides underlie many hillside areas in the region. The combination of 1) having steep slopes made of weak bedrock or soil, 2) modifying the land surface for the construction of homes, and 3) the saturation of the land after intense period of rain can reactivate these ancient slides or create new landslides. Slopes stripped of vegetation, by fire or other means, can be especially vulnerable.
Unlike earthquakes, impending landslides sometimes provide warning signs, according to the Department of Conservation’s California Geological Survey. Residents are advised to know these signs, check for them, and contact local authorities if they are concerned about the potential for landslides:
♦ Check around your home and property for new cracks in the soil, structural shifts within your home, the appearance of holes or bare spots on hills, tilting trees or bulges at the base of slopes, or material moving downhill.
♦ Watch for new springs or seeps and excess surface erosion on slopes on and around your property. If there are nearby streams, do they appear muddier than normal?
♦ Listen for unusual rumbling sounds or noises that may indicate moving earth and rocks or breaking vegetation or structures.
♦ Likewise, noises in your plumbing may indicate that pipes are being pulled apart.
Additional tips to keep in mind during the rainy season:
♦ Stay alert to the amount of rain falling locally during intense rainstorms. Buy a rain gauge (an inexpensive plastic one will suffice) and install it where it can be checked frequently.
♦ Whenever rainfall has exceeded 3 or 4 inches per day or ¼ inch per hour, be aware that the soil may be waterlogged and more rain can trigger mudflows.
♦ The single most important action that should be taken by residents on rainy nights is to avoid sleeping in lower-floor bedrooms on the sides of houses that face hazardous slopes.