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News Release

October 3, 1997
Heidi Koehler 303-236-5900 x302

El Nino May Trigger Landslides... USGS Map Indicates Susceptibility and Incidence of Landslides

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Floods, coastal erosion and heavy precipitation aren’t the only predicted consequences of the El Nino phenomena. Landslides and debris flows could happen in areas where intense rainfall occurs.

To aid in awareness of these hazards, the U.S. Geological Survey has published a digitized version of a national landslide map for the conterminous United States. The map, at a scale of 1:3,750,000, shows landslide susceptibility and incidence. A high-resolution, image file of the map can be downloaded from its website,,or a paper copy can be ordered through USGS publication outlets beginning in mid-October. Information about the map can be obtained by calling the National Landslide Information Center at 303/273-8588.

Landslides, including rockfalls, debris flows, and a variety of other slope movements cause billions of dollars in property losses in the United States, and between 25 and 50 deaths annually, according to USGS scientists. All 50 states have landslide problems to some extent.

"Many people think of landslides as isolated, local events brought about by special sets of unique conditions, occurring sporadically across the landscape," said Lynn Highland, coordinator for the USGS Landslide Information Center in Golden, Colo. "While this perception is partly true, many of the most significant landslides are produced by powerful geologic systems operating on much larger scales."

In addition to landslides and debris flows that occur following heavy rainfall, landslides can be triggered by earthquakes, volcanic eruptions, coastal and river bank erosion, or the buildup of underground water pressures by an accumulation of seasonal rainfall.

The following guidelines reflect what areas are generally prone to landsliding and what residents of these areas should do before and after intense storms. Additional information is provided for residents who live near steep, sloping hills.


Areas that are generally prone to landslide hazards:

Areas that are typically considered safe from landslides:

Features that might be noticed prior to major landsliding:

What to do if you suspect imminent landslide danger:

For further information on landslides in your area:


Prior to Intense Storms:

  1. Become familiar with the land around you. Learn whether debris flows have occurred in your area by contacting local officials, state geological surveys or departments of natural resources, and university departments of geology. Slopes where debris flows have occurred in the past are likely to experience them in the future.

  2. Support your local government in efforts to develop and enforce land-use 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.

  3. Watch the patterns of storm-water drainage on slopes near your home, and note especially the places were 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.

  4. Contact your local authorities to learn about the emergency response and evacuation plans for your area, and develop your own emergency plans for your family and business.

During Intense Storms:

  1. Stay alert and stay awake! Many debris-flow fatalities occur when people are sleeping. Listen to a radio 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.

  2. 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. 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.

  3. If you are in areas susceptible to landslides and debris flows, consider leaving if it is safe to do so. If you remain at home, move to a part of the house farthest away from the source of the debris flows, such as an upper floor, but keep an escape route open should it become necessary to leave the house.

  4. 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.

The USGS serves the nation by providing reliable scientific information to describe and understand the Earth; minimize loss of life and property from natural disasters; manage water, biological, energy, and mineral resources; and enhance and protect our quality of life.

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