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USGS Warns of Landslide Dangers with Isabel
Released: 9/18/2003

Contact Information:
U.S. Department of the Interior, U.S. Geological Survey
Office of Communication
119 National Center
Reston, VA 20192
Michelle Barret 1-click interview
Phone: 601-933-2932

Butch Kinerney
Phone: 703-648-4732

The U.S. Geological Survey today warned state and federal agencies about the increased potential for landslides in the mountainous regions of Virginia, West Virginia, Maryland, Pennsylvania and New York due to rainfall from Hurricane Isabel.

"Given the wet soil conditions we already have in many of these areas, the risk of fast-moving landslides is significant," Wieczorek said. "Residents in landslide-prone areas and anyone in mountainous areas should be aware of the warning signs and be prepared to move quickly."

USGS geologist and landslide expert Gerald Wieczorek said that intense rains have triggered landslides in the area before.

"In August 1969, the remnants of Hurricane Camille, moving eastward across the Appalachian Mountains from the Gulf Coast, dumped at least 28 inches of rain within an 8-hour period," he said. "Landslides and severe floods claimed 150 lives. Property damage was estimated at more than $116 million in Nelson County, Va. This catastrophic storm caused extensive damage to roads, bridges, communication systems, houses, farms, and livestock." Before the storm:

  1. Become familiar with the land around you. Learn whether landslides have occurred in your area. Slopes where landslides have occurred in the past are likely to experience them in the future.
  2. Watch the patterns of storm-water drainage on slopes near your home, and note 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.
  3. 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 the storm:

  1. Stay alert and stay awake. Many landslide 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. If you are in areas susceptible to landslides, consider leaving if it is safe to do so. Remember that driving during an intense storm can itself be hazardous.
  3. 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 flows. 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.
  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. Never drive across a flooded road.

The slope of the land, the type of geology, ground saturation and rainfall intensity all play major roles in landslide formation. As a rule of thumb, Wieczorek said, more than 2.75 inches of rain per hour for 2 hours; more than 2 inches of rain per hour for 4 hours; or more than 1.5 inches of rain per hour for 6 hours could trigger landslides in mountainous areas.

In the summer of 1995, a major landslide occurred in Madison County, Va., during an intense storm in which 30 inches of rain fell in 16 hours. Scientists from USGS identified hundreds of individual debris flows, some traveling as far as 2 miles. Although some landslides are gradual, debris flows are fast-moving landslides that often occur suddenly and cost lives. Rivers throughout the county turned to torrents of mud, cutting off farms and even towns from the outside.

"Landslides are powerful," Wieczorek said. "People living in these areas should be aware of the danger during severe weather and be ready to act if the situation warrants."

For more information, visit the following websites:

Debris-Flow Hazards in the United States: http://pubs.usgs.gov/fs/fs-176-97/fs-176-97.html

Landslide Hazards: http://pubs.usgs.gov/fs/fs-0071-00/

Debris-Flow Hazards in the Blue Ridge of Virginia: http://landslides.usgs.gov/html_files/nlic/blueridge.htm

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