TABLE OF CONTENTS:
Why Talk About Landslides?
Landslides are a serious geologic hazard common to almost every state in the United States. It is estimated that nationally they cause up to $2 billion in damages and 25-50 deaths annually. Globally, they cause billions of dollars in damage and thousands of deaths and injuries each year. Individuals can take steps to reduce their personal risk. Know about the hazard potential where you live, take steps to reduce your risk and practice preparedness plans.
What are Landslides and Debris Flows? What Causes Them?
Debris flows--sometimes referred to as mudslides, mudflows, lahars or debris avalanches--are common types of fast-moving landslides. They are typically associated with periods of heavy rainfall or rapid snow melt and tend to worsen the effects of flooding. Other factors that may initiate them include steepening of slopes by erosion or construction, forest and brush fires that deplete water-absorbing vegetation, alternate freezing or thawing, earthquake shaking and volcanic eruptions. Driven by gravity, these flows usually start on steep hillsides as shallow landslides that liquefy and accelerate to about 10 miles per hour, but can exceed 35 miles per hour. The consistency ranges from watery mud to thick, rocky mud that can carry large items such as boulders, trees and cars. Debris flows from different sources can combine in channels, and their destructive power may be greatly increased. They continue growing in volume with the addition of water, sand, mud, boulders, trees and other materials. When the flows reach flatter ground, the debris spreads over a broad area, sometimes accumulating in thick deposits that can wreak havoc in developed areas.
Among the most destructive types of debris flows are those that accompany volcanic eruptions. A spectacular example in the United States was a massive debris flow resulting from the 1980 eruptions of Mount St. Helens, Washington. Areas near the bases of many volcanoes in the Cascade Mountain Range of California, Oregon and Washington are at risk from the same types of flows during future volcanic eruptions.
Wildfires can also lead to destructive debris-flow activity. In July 1994, a severe wildfire swept Storm King Mountain, west of Glenwood Springs, Colorado, denuding the slopes of vegetation. Heavy rains on the mountain in September resulted in numerous debris flows, one of which blocked Interstate 70 and threatened to dam the Colorado River.
Learn whether landslides or debris flows have occurred in your area by contacting local officials, state geological surveys or departments of natural resources and university departments of geology.
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Awareness Information
Areas that are generally prone to landslide hazards include existing old landslides; the bases of steep slopes; the bases of drainage channels; and developed hillsides where leach-field septic systems are used.
Areas that are typically considered safe from landslides include those that have not moved in the past; relatively flat spaces away from sudden changes in slope; and areas at the top or along ridges, set back from the tops of slopes.
Learn what to watch for prior to major landsliding. Look for patterns of storm-water drainage on slopes near your home, noting especially the places where runoff water converges, increasing flow over soil-covered slopes. Check hillsides around your home for any signs of land movement, such as small landslides or debris flows or progressively tilting trees.
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Plan for a Landslide
Develop a Family Disaster Plan. Develop landslide-specific
planning. Learn about landslide risk in your area. 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 detailed analysis of your property, and corrective measures you can take, if necessary. Also, assemble a disaster supplies kit.
If you are at risk from landslides:
- Talk to your insurance agent. Debris flow may be covered by flood insurance policies from the National Flood Insurance Program (NFIP).
- Develop an evacuation plan. You should know where to go if you have to leave. Trying to make plans at the last minute can be upsetting and create confusion.
- Discuss landslides and debris flow with your family. Everyone should know what to do in case all family members are not together. Discussing disaster ahead of time helps reduce fear and lets everyone know how to respond during a landslide or debris flow.
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How to Protect Your Property
- If your property is in a landslide-prone area, contract with a private consulting company specializing in earth movement for opinions and advice on landslide problems and on corrective measures you can take. Such companies would likely specialize in geotechnical engineering, structural engineering or civil engineering. Local officials could possibly advise you as to the best kind of professional to contact in your area. Taking steps without consulting a professional could make your situation worse.
- Install flexible pipe fittings to avoid gas or water leaks. Flexible fittings will be less likely to break.
Media and Community Education Ideas
- In an area prone to landslides, publish a special newspaper section with emergency information on landslides and debris flows. Localize the information by including the phone numbers of local emergency
services offices, the American Red Cross chapter and hospitals.
- Report on what city and county governments are doing to reduce the possibility of landslides. Interview local officials about local land-use zoning regulations.
- Interview local officials and major insurers regarding the National Flood Insurance Program. Find out if debris flow is covered by NFIP flood insurance policies and contact your local emergency management office to learn more about the program.
- Work with local emergency services and American Red Cross officials to prepare special reports for people with mobility impairments on what to do if evacuation is ordered.
- Support your local government in efforts to develop and enforce landuse and building ordinances that regulate construction in areas susceptible to landslides and debris flows. Buildings should be located away from steep slopes, streams and rivers, intermittent-stream channels and the mouths of mountain channels.
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What to Do Before Intense Storms
- Become familiar with the land around you to better assess your risk of danger. Learn whether landslides and debris flows have occurred in your area by contacting local officials, state geological surveys or departments of natural resources and university departments of geology.
- Watch the patterns of storm-water drainage on slopes near your home, and especially the places where 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. These could alert you to the potential of a greater threat.
What to Do During Intense Storms
- Stay alert and awake. Many debris-flow fatalities occur when people are sleeping. Listen to a National Oceanic and Atmospheric Administration (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. Embankments along roadsides are particularly susceptible to landslides. Watch the road for collapsed pavement, mud, fallen rocks and other indications of possible debris flows.
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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.
What to Do During a Landslide
- Quickly move out of the path of the landslide or debris flow. Moving to a stable area will reduce your risk.
- If escape is not possible, curl into a tight ball and protect your head. This position will provide the best protection for your body.
What to Do After a Landslide
- Stay away from the slide area. There may be danger of additional slides.
- Check for injured and trapped persons near the slide, without entering the direct slide area. Direct rescuers to their locations.
- Help neighbors who may require special assistance--infants, seniors and people with disabilities. People who care for them or who have large families may need additional assistance.
- 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 because they may be started by the same event.
- Look for and report broken utility lines 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. Such damage 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.
- Seek the advice of 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.
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Produced by the National Disaster Education Coalition: American Red Cross, Federal Emergency Management Agency, International Association of Emergency Managers, Institute for Business and Home Safety, National Fire Protection Association, National Weather Service, United States Department of Agriculture/Cooperative State Research, Education and Extension Service and United States Geological Survey
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