Landslides
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Landslides 
 

As population expands into once sparsely populated rural forests and agricultural lands, the need for mapping and understanding landslides becomes increasingly urgent. Coupled with climatic change prediction for more frequent and intense storm events, mapping and understanding geologic hazards can greatly reduce impacts to infrastructure, loss of life, and property. Although we do not have an exact estimate of damage landslides have caused in Washington, a rough estimate from only large storm systems and earthquakes is in billions of dollars. The potential damage from landslides is tens to hundreds of billions of dollars. In 1998, the Aldercrest-Banyon landslide alone damaged or destroyed 138 homes and accounted for $30-40 million in losses. Nationally, landslides account over $2 billion of loss annually and result in an estimated 25 to 50 deaths a year.

Pe Ell landslide from the December 3rd stormAlthough landslides have caused widespread damage across the United States (including Washington State), they are often underrepresented and understudied compared to other potential geologic hazards, such as earthquakes, tsunamis, and volcanoes. Landslides are complex, often moving in numerous different ways, from small shallow slumps and rock topples to deep-seated landslides. Understanding how and why these landslides move help scientists develop mitigation techniques for some landslides and help determine future hazards for roads, houses, and infrastructure.

The Geology and Earth Resources Division is helping to increase understanding of landslide processes in Washington State through numerous research projects. Our main research project on landslides is on Puget Sound basin landslide processes to help counties with their urban growth areas and critical areas ordinances. Landslides hazards in tsunami evacuation zones are also being studied along with other associated hazards, such as liquefaction and tsunami inundation areas.

Landslides exist throughout Washington State and can be triggered in many ways. The most common in Washington State appears to be during prolonged or high-intensity rain events, such as the storm on December 3rd, 2007. Earthquakes have also triggered numerous landslides. The earthquakes of 1949, 1965, and the Nisqually earthquake of 2001 produced numerous landslides throughout the Puget Sound basin. Other potential triggers in Washington State include loss of rooting strength (harvest and forest fires), rain-on-snow events, and human influences.

Landslides are a continuing problem along the hillsides and shorelines of Washington. Some landslide areas and their causes of sliding have been recognized for decades, but that information has not always been widely known or used outside the geologic community. As the population of Washington grows, there are increasing pressures to develop in landslide-prone areas, so knowledge about these landslide hazards has never been more important.

Have you seen a landslide?  Report it here

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 Contacts

Stephen Slaughter
Geology & Earth Resources Division, Hazards Geologist
Washington State Department of Natural Resources
360-902-1498
Fax 360-902-1785
stephen.slaughter@dnr.wa.gov

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