Landslide and Debris Flow (Mudslide)
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Why Talk About Landslides?
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Landslides are a serious geologic hazard common to almost
in the United States. It is estimated that nationally they cause up to
$2 billion in damages and from 25 to 50 deaths annually. Globally,
landslides cause billions of dollars in damage and thousands of deaths
and injuries each year. Individuals can take steps to reduce their
risk. Know about the hazard potential where you live, take steps to
your risk, and practice preparedness plans.
What Are Landslides and Debris Flows, and What Causes Them?
Some landslides move slowly and cause damage gradually, whereas others
move so rapidly that they can destroy property and take lives suddenly
and unexpectedly. Gravity is the force driving landslide movement.
that allow the force of gravity to overcome the resistance of earth
to landslide movement include: saturation by water, steepening of
by erosion or construction, alternate freezing or thawing, earthquake
and volcanic eruptions.
Landslides are typically associated with periods of heavy
rapid snow melt and tend to worsen the effects of flooding
accompanies these events. In areas burned by forest and brush fires, a
lower threshold of precipitation may initiate landslides.
Debris flows, sometimes referred to as mudslides,
or debris avalanches, are common types of fast-moving landslides.
flows generally occur during periods of intense rainfall or rapid snow
melt. They usually start on steep hillsides as shallow landslides that
liquefy and accelerate to speeds that are typically about 10 miles per
hour, but can exceed 35 miles per hour. The consistency of debris flows
ranges from watery mud to thick, rocky mud that can carry large items
as boulders, trees, and cars. Debris flows from many different sources
can combine in channels, and their destructive power may be greatly
They continue flowing down hills and through channels, growing in
with the addition of water, sand, mud, boulders, trees, and other
the flows reach flatter ground, the debris spreads over a broad area,
accumulating in thick deposits that can wreak havoc in developed areas.
Among the most destructive types of debris flows are those
volcanic eruptions. A spectacular example in the United
a massive debris flow resulting from the 1980 eruptions of Mount St.
Washington. Areas near the bases of many volcanoes in the Cascade
Range of California, Oregon, and Washington are at risk from the same
of flows during future volcanic eruptions.
Wildfires can also lead to destructive debris-flow
July 1994, a severe wildfire swept Storm King Mountain, west of
Springs, Colorado, denuding the slopes of vegetation. Heavy rains on
mountain in September resulted in numerous debris flows, one of which
Interstate 70 and threatened to dam the Colorado River.
Learn whether landslides or debris flows have occurred in
by contacting local officials, state geological surveys or departments
of natural resources, and university departments of geology.
Areas that are generally prone to landslide hazards include
old landslides; the bases of steep slopes; the bases of drainage
and developed hillsides where leach-field septic systems are used.
Areas that are typically considered safe from landslides
areas that have not moved in the past; relatively flat-lying areas 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
such as small landslides or debris flows or progressively tilting trees.
Plan for a Landslide
Develop a Family Disaster Plan. Please see the "Family
Disaster Plan"section for general family planning
landslide-specific planning. Learn about landslide risk in
Contact local officials, state geological surveys or departments of
resources, and university departments of geology. Landslides occur
they have before, and in identifiable hazard locations. Ask for
on landslides in your area, specific information on areas vulnerable to
landslides, and request a professional referral for a very detailed
analysis of your property, and corrective measures you can take, if
If you are at risk from landslides:
Please see the section "Disaster
general supplies kit information. Landslide-specific supplies should
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. (See "Evacuation"
in the "Family Disaster Plan" section.) You should know where to go if
you have to leave. Trying to make plans at the last minute can be
and create confusion.
Discuss landslides and debris flow with your family.
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.
Disaster Suplies Kit basics.
Evacuation Supplies Kit.
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
on landslide problems and on corrective measures you can take.
companies would likely be those specializing in geotechnical
structural engineering, or civil engineering. Local officials could
advise you as to the best kind of professional to contact in your area.
Taking steps without consulting a professional could make your
Install flexible pipe fittings to avoid gas or water leaks.
fittings will be less likely to break.
Media and Community Education Ideas
In an area prone to landslides, publish a special newspaper section
emergency information on landslides and debris flows. Localize the
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
of landslides. Interview local officials about local land- use zoning
Interview local officials and major insurers regarding the National
Flood Insurance Program. Find out if debris flow is covered
insurance policies from the National Flood Insurance Program and
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
impairments on what to do if evacuation is ordered.
Support your local government in efforts to develop and enforce
and building ordinances that regulate construction in areas susceptible
to landslides and debris flows. Buildings should be located away from
slopes, streams and rivers, intermittent-stream channels, and the
of mountain channels.
What to Do Before Intense Storms
Become familiar with the land around you. Learn
and debris flows have occurred in your area by contacting local
state geological surveys or departments of natural resources, and
departments of geology. Knowing the land can help you assess your risk
Watch the patterns of storm-water drainage on slopes near
and especially the places where runoff water converges, increasing flow
over soil-covered slopes. Watch the hillsides around your
any signs of land movement, such as small landslides or debris flows,
progressively tilting trees. Watching small changes could alert you to
the potential of a greater landslide threat.
What to Do During Intense Storms
Stay alert and awake. Many debris-flow
fatalities occur when people
are sleeping. Listen to a NOAA
Radio or portable, battery-powered radio or television for
of intense rainfall. Be aware that intense, short bursts of rain may be
particularly dangerous, especially after longer periods of heavy
and damp weather.
If you are in areas susceptible to landslides and debris
leaving if it is safe to do so. Remember that driving during
storm can be hazardous. If you remain at home, move to a second story
possible. Staying out of the path of a landslide or debris flow saves
Listen for any unusual sounds that might indicate moving
as trees cracking or boulders knocking together. A trickle of
or falling mud or debris may precede larger landslides. Moving debris
flow quickly and sometimes without warning.
If you are near a stream or channel, be alert for any
or decrease in water flow and for a change from clear to muddy water.
Such changes may indicate landslide activity upstream, so be prepared
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
mud, fallen rocks, and other indications of possible debris flows.
What to Do if You Suspect Imminent Landslide Danger
Contact your local fire, police, or public works
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 Lanslide
Quickly move out of the path of the landslide or debris
away from the path of the flow to a stable area will reduce your risk.
If escape is not possible, curl into a tight ball and
protect your head.
A tight ball 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
Check for injured and trapped persons near the slide,
the direct slide area. Direct rescuers to their locations.
Help a neighbor who may require special assistance -
people, and people with disabilities. Elderly people and
disabilities may require additional assistance. People who care for
or who have large families may need additional assistance in emergency
Listen to local radio or television stations for the
Watch for flooding, which may occur after a landslide or
Floods sometimes follow landslides and debris flows because they may
be started by the same event.
Look for and report broken utility lines to appropriate
Reporting potential hazards will get the utilities turned off as
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
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
or designing corrective techniques to reduce landslide risk.
will be able to advise you of the best ways to prevent or reduce
risk, without creating further hazard.
Produced by the National
Disaster Education Coalition:
Red Cross, FEMA,
and USGS. HTML
formating By the
From: Talking About Disaster: Guide for Standard
by the National Disaster Education Coalition, Washington, D.C., 1999.
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