Text from USGS, modified and supplemented by BYU-Idaho faculty

Portugese Bend landslide complex, Palos Verdes peninsula, southern California (BYUI)

Learning Objectives Landslides are common problems across the country and in many parts of the world. Next to flooding, they are the most likely natural hazard you may have to deal with in your lifetime. Your goals for studying this chapter are:

• Understand where landslides occur.

• Understand the warning signs of landslides.

• Understand what to do in the event of a landslide.

• Understand the basic types of landslides and related

terminology.

• Understand the geologic and man-made causes of

landslides.

• Understand landslide mitigation measures and how they

are best applied.

(Utah Geological Survey)

Where do Landslides Occur? (USGS)

Landslides occur in every state and U.S. territory. The Appalachian Mountains, the Rocky Mountains and the Pacific

Coastal Ranges and some parts of Alaska and Hawaii have severe landslide problems. Any area composed of very weak

or fractured materials resting on a steep slope can and will likely experience landslides.

Although the physical cause of many landslides cannot be removed, geologic investigations, good engineering practices,

and effective enforcement of land-use management regulations can reduce landslide hazards.

USGS scientists continue to produce landslide susceptibility maps for many areas in the United States. In every state,

USGS scientists monitor streamflow, noting changes in sediment load carried by rivers and streams that may result from

landslides. Hydrologists with expertise in debris and mud flows are studying these

Why Study Landslides?

Landslides are a serious geologic hazard common to

almost every State in the United States. It is estimated

that in the United States, they cause in excess of $1

billion in damages and from about 25 to 50 deaths each

year. Globally, landslides cause hundreds of billions of

dollars in damages and hundreds of thousands of deaths and

injuries each year.

The National Landslide Information Center, developed by

the U.S. Geological Survey, is a multifunctional enterprise

dedicated to collection and distribution of all forms of

information related to landslides. It is designed to serve

landslide researchers, geotechnical practitioners engaged in

landslide stabilization, and all other people and entities

concerned in any way with landslide hazards analysis and

mitigation. Palos Verdes peninsula, southern California (BYUI)

Go to USGS http://landslides.usgs.gov/state_local/nationalmap/ for the interactive version of this map.

What is a Landslide?

The term landslide (or mass wasting, or mass movement) includes a wide range of ground movement such as rockfalls,

rock avalanches, slumps, mud flows, and debris flows. Although gravity acting on an over-steepened slope is the primary

reason for a landslide, there are other contributing factors:

-erosion by rivers, glaciers, or ocean waves create over-steepened slopes

-rock and soil slopes are weakened through saturation by snowmelt or heavy rains

-earthquakes create stresses that make weak slopes fail

-volcanic eruptions produce loose ash deposits and lahars

-excess weight from accumulation of rain or snow, stockpiling of rock or ore, from waste piles, or from man-made

structures may stress weak slopes to failure and other structures

Landslide Preparedness

Landslide Warning Signs

• 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.

• Rapid increase in creek water levels, possibly accompanied by increased turbidity (soil content).

• 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.

• A faint rumbling sound that increases in volume is noticeable as the landslide nears.

• Unusual sounds, such as trees cracking or boulders knocking together, might indicate moving debris.

(USGS)

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.

Areas that are typically considered safe from landslides

• On hard, unfractured 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.

El Salvador (USGS)

What To Do Before a Landslide

• 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.

(USGS)

What To Do During a Landslide

• 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. (USGS)

(USGS)

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.

(USGS)

What To Do After a Landslide

• 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.

(USGS)