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What are Landslides?


Landslides are rock, earth, or debris flows on slopes due to gravity. They can occur on any terrain given the right conditions of soil, moisture, and the angle of slope. Integral to the natural process of the earth's surface geology, landslides serve to redistribute soil and sediments in a process that can be in abrupt collapses or in slow gradual slides. Such is the nature of the earth's surface dynamics. Also known as mud flows, debris flows, earth failures, slope failures, etc., they can be triggered by rains, floods, earthquakes, and other natural causes as well as human-made causes, such as grading, terrain cutting and filling, excessive development, etc. Because the factors affecting landslides can be geophysical or human-made, they can occur in developed areas, undeveloped areas, or any area where the terrain was altered for roads, houses, utilities, buildings, and even for lawns in one's backyard.

Areas that are generally prone to landslides


* On existing landslides, old or recent
* On or at the base or top 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


Areas that are generally safe from landslides


* On hard, non-jointed bedrock that has not moved in the past
* On relatively flat-lying areas away from slopes and steep river banks
* At the top or along the nose of ridges, set back from the tops of slopes


Features that might be noticed before major landslides


* 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
* 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

What to do if you suspect immediate landslide danger


* Contact your local fire, police or public works department
* Inform affected neighbors
* Leave the area quickly
* Contact a consulting geologist

Safety Tips:  

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 be those specializing 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.

What to Do Before Intense Storms

Become familiar with the land around you. 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. Knowing the land can help you assess your risk for danger.

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. 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 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.


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 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 slides.

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.

Listen to local radio or television stations for the latest emergency information.

Additional Information
http://walrus.wr.usgs.gov/elnino/landslide-guidelines.html

© 2008 - Department of Meteorology, 383, Bauddhaloka Mawatha, Colombo 07, Sri Lanka.
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