Introduction
During past El Niño seasons, landslides and debris flows were a major hazard.
The following guidelines reflect what areas are generally prone to landslides, and what residents of these areas should do before, during, and after intense storms. Additional information is provided for residents who live near steep hills.
These guidelines are generalized.
Many areas have specific landslide concerns. Check the information section below for details.
Areas that are generally prone to landslides
- On existing landslides, old or recent
- On or at the base or top of slopes
- In or at the base of minor drainage hollows
- At the base or top of an old fill slope
- At the base or top of a steep cut slope
Areas that are generally safe from landslides
- On hard, non-jointed bedrock that has not moved in the past
- On relatively flat-lying areas away from slopes and steep river banks
- At the top or along the nose of ridges, set back from the tops of slopes
Features that might be noticed before major landslides
- Springs, seeps, or saturated ground in areas that have not typically been wet before
- New cracks or unusual bulges in the ground, street pavements or sidewalks
- Soil moving away from foundations
- Ancillary structures such as decks and patios tilting and/or moving relative to the main house
- Tilting or cracking of concrete floors and foundations
- Broken water lines and other underground utilities
- Leaning telephone poles, trees, retaining walls or fences
- Offset fence lines
- Sunken or down-dropped road beds
- Sudden decrease in creek water levels though rain is still falling or just recently stopped.
- Sticking doors and windows, and visible open spaces indicating jambs and frames out of plumb
What to do if you suspect immediate landslide danger
- Contact your local fire, police or public works department
- Inform affected neighbors
- Leave the area quickly
- Contact a consulting geologist
If you live near steep hills
Before Intense Storms
- Become familiar with the land around you. Learn whether landslides or debris flows have occurred in your area by contacting local officials, state geological surveys or departments of natural resources, USGS maps, and university departments of geology. Slopes where landslides or debris flows have occurred in the past are likely to experience them in the future.
- Support your local government in efforts to develop and enforce land-use and building ordinances that regulate construction in areas susceptible to landslides and debris flows. Buildings should be located away from known landslides, debris flows, steep slopes, streams and rivers, intermittent-stream channels, and the mouths of mountain channels.
- Watch the patterns of storm-water drainage on slopes near your home, and note especially the places were runoff water converges, increasing flow over soil-covered slopes. Watch the hillsides around your home for any signs of land movement, such as small landslides or debris flows or progressively tilting trees.
- Contact your local authorities to learn about the emergency response and evacuation plans for your area, and develop your own emergency plans for your family and business.
During Intense Storms
- Stay alert and stay awake! Many landslide and debris flow fatalities occur when people are sleeping. Listen to a radio for warnings of intense rainfall. Be aware that intense short bursts of rain may be particularly dangerous, especially after longer periods of heavy rainfall and damp weather.
- Listen for any unusual sounds that might indicate moving debris, such as trees cracking or boulders knocking together. A trickle of flowing or falling mud or debris may precede larger landslides. If you are near a stream or channel, be alert for any sudden increase or decrease in water flow. Such changes may indicate landslide activity upstream, so be prepared to move quickly. Don't delay! Save yourself, not your belongings.
- If you are in areas susceptible to landslides and debris flows, consider leaving if it is safe to do so. If you remain at home, move to a part of the house farthest away from the source of the landslide or debris flows, such as an upper floor, but keep an escape route open should it become necessary to leave the house.
- Be especially alert when driving. Embankments along roadsides are particularly susceptible to landslides. Watch the road for collapsed pavement, mud, fallen rocks, and other indications of possible landslides or debris flows.
After Intense Storms
- Keep looking for signs that the land is moving. Landslides can occur weeks or months after intense storms.
For more information on landslides
- Contact your state or county geologist - some cities also have staff geologists.
- If a very detailed site analysis is desired, contract with a private consulting company that specializes in earth movement. Such companies would likely be those specializing in geotechnical engineering, structural engineering, or civil engineering. Your local, state or county geologist can usually advise you as to the best kind of professional to contact.
- Visit the USGS National Landslide Information Center
- For past studies on landslides:
- Find more USGS information on Landslides
Source: USGS Press Release, 3 October 1997.
USGS El Niño Home Page
URL: http://walrus.wr.usgs.gov/elnino/landslide-guidelines.html
Maintained by: Laura Zink Torresan
Last modified: 15 October (lzt)
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