Landslide

The U.S. Geological Survey defines landslides to include a wide range of ground movement, such as rock falls, deep failure of slopes, and shallow debris flows. Although gravity acting on an over-steepened slope is the primary reason for a landslide, there are other contributing factors.

Landslides and mudslides can be initiated by storms, earthquakes, fires, volcanic eruptions, or human modification of the land. They can move rapidly down slopes or through channels and can strike with little or no warning at avalanche speeds, posing a serious hazard to properties on or below hillsides.

When landslides occur—in response to such changes as increased water content, earthquake shaking, addition of load, or removal of downslope support—they deform and tilt the ground surface. The result can be destruction of foundations, offset of roads, breaking of underground pipes, or overriding of downslope property and structures.

SAFER: Areas that are typically considered safe from landslides

  • On hard, non-jointed bedrock that has not moved in the past.

  • On relatively flat-lying areas away from sudden changes in slope angle.

  • At the top or along the nose of ridges, set back from the tops of slopes.

LESS SAFE: Areas that are generally prone to landslide hazards

  • On existing old landslides.

  • On or at the base 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.

  • Developed hillsides where leach field septic systems are used.

    What Can You do? Prepare for Landslides

    BEFORE

    • Do not build near steep slopes, close to mountain edges, near drainage ways, or natural erosion valleys.
    • Get a ground assessment of your property.
    • Contact local officials, state geological surveys or departments of natural resources, and university departments of geology. Landslides occur where they have before, and in identifiable hazard locations. Ask for information on landslides in your area, specific information on areas vulnerable to landslides, and request a professional referral for a very detailed site analysis of your property, and corrective measures you can take, if necessary.
    • Watch the patterns of storm-water drainage near your home, and note the places where runoff water converges, increasing flow in channels. These are areas to avoid during a storm.
    • Learn about the emergency-response and evacuation plans for your area. Develop your own emergency plan for your family or business.
    • Minimize home hazards:
      • Have flexible pipe fittings installed to avoid gas or water leaks, as flexible fittings are more resistant to breakage (only the gas company or professionals should install gas fittings).
      • Plant ground cover on slopes and build retaining walls.
      • In mudflow areas, build channels or deflection walls to direct the flow around buildings. Remember: If you build walls to divert debris flow and the flow lands on a neighbor's property, you may be liable for damages.

    DURING

    • Stay alert and awake. Many debris-flow fatalities occur when people are sleeping. Listen to a NOAA Weather Radio or portable, battery-powered radio or television 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.
    • If you are in areas susceptible to landslides and debris flows, consider leaving if it is safe to do so. Remember that driving during an intense storm can be hazardous. If you remain at home, move to a second story if possible. Staying out of the path of a landslide or debris flow saves lives.
    • 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. Moving debris can flow quickly and sometimes without warning.
    • If you are near a stream or channel, be alert for any sudden increase or decrease in water flow and for a change from clear to muddy water. Such changes may indicate landslide activity upstream, so be prepared to move quickly. Don't delay! Save yourself, not your belongings.
    • Be especially alert when driving. Bridges may be washed out, and culverts overtopped. Do not cross flooding streams!! Turn Around, Don't Drown®!. Embankments along roadsides are particularly susceptible to landslides. Watch the road for collapsed pavement, mud, fallen rocks, and other indications of possible debris flows.
    • Be aware that strong shaking from earthquakes can induce or intensify the effects of landslides.

    What to Do if You Suspect Imminent Landslide Danger

    • Contact your local fire, police, or public works department. Local officials are the best persons able to assess potential danger.
    • Inform affected neighbors. Your neighbors may not be aware of potential hazards. Advising them of a potential threat may help save lives. Help neighbors who may need assistance to evacuate.
    • Evacuate. Getting out of the path of a landslide or debris flow is your best protection.
    • Curl into a tight ball and protect your head if escape is not possible.

    AFTER

    • Stay away from the slide area. There may be danger of additional slides.
    • Listen to local radio or television stations for the latest emergency information.
    • Watch for flooding, which may occur after a landslide or debris flow. Floods sometimes follow landslides and debris flows because they may both be started by the same event.
    • Check for injured and trapped persons near the slide, without entering the direct slide area. Direct rescuers to their locations.
    • Help a neighbor who may require special assistance - infants, elderly people, and people with disabilities. Elderly people and people with disabilities may require additional assistance. People who care for them or who have large families may need additional assistance in emergency situations.
    • Look for and report broken utility lines and damaged roadways and railways to appropriate authorities. Reporting potential hazards will get the utilities turned off as quickly as possible, preventing further hazard and injury.
    • Check the building foundation, chimney, and surrounding land for damage. Damage to foundations, chimneys, or surrounding land may help you assess the safety of the area.
    • Replant damaged ground as soon as possible since erosion caused by loss of ground cover can lead to flash flooding and additional landslides in the near future.
    • Seek advice from a geotechnical expert for evaluating landslide hazards or designing corrective techniques to reduce landslide risk. A professional will be able to advise you of the best ways to prevent or reduce landslide risk, without creating further hazard.

     

    What Can You do? Prepare for Landslides

    The City of Cupertino works to mitigate the risk of landslides through mitigation, preparedness, response and recovery efforts

    MITIGATION

    Infrastructural maintenance and upgrades, summarized in the City Work Program, target slope stability, evacuation route hardening, and other projects aimed at shoring up infrastructural vulnerabilities in a catastrophic event.

    PREPAREDNESS

    The City offers personal and family emergency preparedness training to residents throughout the year.  The Public Safety Forum, hosted for the City each October, provides residents an array of public safety and preparedness resources to use before or during an event like a landslide.  Visit the City Calendar to view and register for these, and other public safety events.

    RESPONSE

    The City coordinates with special districts and non-governmental organizations like the American Red Cross to prepare to staff shelters in the event of an emergency where people are displaced.  In 2023 the Red Cross and the City Office of Emergency Management collaborated on training City staff to support care and sheltering operations.

    The City Office of Emergency Management develops and maintains the Emergency Operations Plan, Continuity of Operations Plan, and Multijurisdictional Hazard Mitigation Plan.  Learn more about these plans, and the role they play guiding emergency management on our Plans page. Provide feedback on plan development and maintenance.

    RECOVERY

    The City is prepared to support the community throughout the recovery process, connecting residents with local, state, and federal resources when they are available.

     

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