June 29, 1999 Scenic rock cliffs falling to valley floors, rocks ripping out mountainsides, mud and debris moving down valleys at deadly speeds, mines and caves collapsing, and ocean and river bluffs sliding into the water -- all describe one of the nation's most underestimated hazards -- landslides. Scientists funded by the U.S. Geological Survey's National Landslide Hazards Program are attempting to reduce long-term losses from these hazards by improving our understanding of the causes of ground failure and refining mitigation strategies.
Major rockfalls have been the main geological culprit in the landslide family of late. In the last month, at least 10 fatalities have resulted from rockfalls in Hawaii, Colorado, and California. On May 9, a rockfall at Sacred Falls State Park in Hawaii killed eight sightseers and injured more than 30 others. In mid-May, plummeting rocks killed a woman along Interstate 70 near Georgetown, Colo. And recently, on June 13, 525 tons of plunging rocks fell near Curry Village at Yosemite National Park, Calif., leaving one 22-year-old rock climber dead and injuring several others.
The geologic features that make Yosemite Valley such a special visual experience are the same that make it hazardous. The Village area in Yosemite Valley is built on the debris of prehistoric rockfalls. Employee housing located there continues to be threatened. According to Dr. Gerald Wieczorek, USGS geologist, "The natural cracking and shearing of the beautiful, but potentially deadly, granite bodes more rockfall events, probably in the near future." Dr. Wieczorek's observations are based on a June 14-16 site visit and his studies of historic landslides of the Yosemite area. Dr. Wieczorek has worked closely with the National Park Service as they monitor the area and provide for the safety of park visitors and employees.
The Yosemite National Park rockfalls are a common phenomenon closely watched and studied by Dr. Wieczorek and other USGS landslide experts. Sculpted by glaciers, the valley is a bowl surrounded by walls of sheer granite. Glacier Point, the site of the most recent rockfalls, rises more than 3,000 feet from the valley floor to a height of 7,214 feet above sea level.
Landslides affect all 50 states and the U.S. territories. At least half of the states, including Alaska and Hawaii, have significant problems. World-wide, landslides are responsible for at least 600 deaths annually, and in the 20th century catastrophic landslides have destroyed entire villages, killing upwards of 20,000 people at a time. Landslides, flows, collapses, and other forms of ground failure are a hazard that virtually all states have in common. Ohio, New York, Utah, Montana, and Kentucky have had numerous run-ins with landslides, as well as those states that have highly populated areas on high bluffs along the Mississippi and Missouri Rivers. The wildfire and rainfall cycle intensifies the hazards of landslides and debris flows in many western states, such as New Mexico, California, and Colorado. These geologic threats are not limited to the coastal and high mountain areas of the country. In June of 1995, a series of severe thunderstorms with heavy rainfall caused landslides, debris flows, and flooding in Madison County, Virginia, where an estimated 1,700-2,000 houses were badly damaged or destroyed.
The economic costs of landslides in the U.S. are conservatively estimated between $1 and $2 billion with 25 to 50 casualties per year. The 1997-98 El Niño-related landslide damage in the 10 San Francisco area counties was assessed at more than $140 million. Add the shaking from even a moderate earthquake to the equation and a double disaster could occur.
Landslides wreak havoc along highway and railroad lifelines, disrupt utility lines, destroy animal habitat, and pollute rivers and streams. They are the bane of urban planners and building officials charged with designing future building sites, managing current urban growth, and providing for safer communities.
The research conducted by the USGS is crucial in providing the basis for the prevention of deaths and the reduction of economic losses from landslides. USGS scientists are currently designing monitoring systems that will provide real-time information on the state of movement of landslide sites, a technology that can be passed along to local officials. Landslide Program geologists are working closely with the Federal Emergency Management Agency (FEMA), and local and state officials in the state of Washington to help generate local responsibility for landslide hazard management. The USGS scientists also work closely with the National Park Service, U.S. Forest Service, NASA, American Planning Association, state geological surveys, and state departments of transportation to provide the geologic information that will assist planners and decision makers at all levels.
Updated information, graphics, and photos about recent landslide events can be found at:
The USGS report, "A Method for Producing Digital Probabilistic Seismic Landslide Hazard Maps: An Example from the Los Angeles, California, Area," can be obtained by calling 1-888-ASK-USGS.
As the nation's largest water, earth and biological science and civilian mapping agency, the USGS works in cooperation with more than 2,000 organizations across the country to provide reliable, impartial, scientific information to resource managers, planners, and other users. This information is gathered in every state by USGS scientists to minimize the loss of life and property from natural disasters, contribute to the sound conservation, economic and physical development of the nation's natural resources, and enhance the quality of life by monitoring water, biological, energy, and mineral resources.
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