What
landslides and debris flows are
Landslides occur when masses of rock, earth, or debris move down
a slope. Debris flows, also known as mudslides, are
a common type of fast-moving landslide that tends to flow in channels.
What
causes landslides and debris flows
Landslides are caused by disturbances in the natural stability of a slope.
They can accompany heavy rains or follow droughts, earthquakes, or volcanic
eruptions. Mudslides develop when water rapidly accumulates in the ground
and results in a surge of water-saturated rock, earth, and debris. Mudslides
usually start on steep slopes and can be activated by natural disasters.
Areas where wildfires or human modification of the land have destroyed
vegetation on slopes are particularly vulnerable to landslides during
and after heavy rains.
Health
threats from landslides and debris flows
In the United States, landslides and debris flows result in 25 to 50 deaths
each year. The health hazards associated with landslides and mudflows
include:
- Rapidly
moving water and debris that can lead to trauma;
- Broken
electrical, water, gas, and sewage lines that can result in injury or
illness; and
- Disrupted
roadways and railways that can endanger motorists and disrupt transport
and access to health care.
What
areas are at risk
Some areas are more likely to experience landslides or mudflows, including:
- Areas
where wildfires or human modification of the land have destroyed vegetation;
- Areas
where landslides have occurred before;
- Steep
slopes and areas at the bottom of slopes or canyons;
- Slopes
that have been altered for construction of buildings and roads;
- Channels
along a stream or river; and
- Areas
where surface runoff is directed.
What
you can do to protect yourself
Before
intense storms and rainfall
- Assume
that steep slopes and areas burned by wildfires are vulnerable to landslides
and debris flows.
- Learn
whether landslides or debris flows have occurred previously in your
area by contacting local authorities, a county geologist or the county
planning department, state geological surveys or departments of natural
resources, or university departments of geology.
- Contact
local authorities about emergency and evacuation plans.
- Develop
emergency and evacuation plans for your family and business.
- Develop
an emergency communication plan in case family members are separated.
- If you
live in an area vulnerable to landslides, consider leaving it.
During
intense storms and rainfall
- Listen
to the radio or watch TV for warnings about intense rainfall or for
information and instructions from local officials.
- Be aware
of any sudden increase or decrease in water level on a stream or creek
that might indicate debris flow upstream. A trickle of flowing mud may
precede a larger flow.
- Look for
tilted trees, telephone poles, fences, or walls, and for new holes or
bare spots on hillsides.
- Listen
for rumbling sounds that might indicate an approaching landslide or
mudflow.
- Be alert
when driving. Roads may become blocked or closed due to collapsed pavement
or debris.
- If landslide
or debris flow danger is imminent, quickly move away from the path of
the slide. Getting out of the path of a debris flow is your best protection.
Move to the nearest high ground in a direction away from the path. If
rocks and debris are approaching, run for the nearest shelter and take
cover (if possible, under a desk, table, or other piece of sturdy furniture).
After
a landslide or debris flow
- Stay
away from the site. Flooding or additional slides may occur after a
landslide or mudflow.
- Check
for injured or trapped people near the affected area, if it is possible
to do so without entering the path of the landslide or mudflow.
- Listen
to the radio or TV for emergency information.
- Report
broken utility lines to the appropriate authorities.
- Consult
a geotechnical expert (a registered professional engineer with soils
engineering expertise) for advice on reducing additional landslide problems
and risks. Local authorities should be able to tell you how to contact
a geotechnical expert.
Where
you can get additional information on landslide and mudflow hazards
The Federal
Emergency Management Agency (FEMA) has a fact sheet containing information
on landslides and mudflows in the United States, as well as recommendations
on how to prepare and behave during and after a landslide.
The U.S.
Geological Survey (USGS) has a fact sheet containing information on
landslide hazards and characteristics.
The American
Red Cross (ARC) has a Web site containing information on landslides
and mudslides.
The United
States Geological Survey (USGS) landslide news Web site provides up-to-date
information on recent and past landslide events.
For information
about reducing losses from landslides at the national, state, and local
levels, in both public and private sectors, review the following document:
Spiker EC, Gori PL. National
landslide hazards mitigation strategy -- a framework for loss reduction.
U.S. Geological Survey Circular 1244 - Online Version 1.0, 2003.
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