Landslides occur in every county in Washington State and amount to 1.5%-2% of Washington State. Every year, landslides impact houses and block or destroy roads and highways. Sparse records exist for where landslides have occurred in the past and no comprehensive records have been kept as to how much damage landslides cause each year, or the impacts that they have.
As population expands into once sparsely developed rural forests and agricultural lands, and climatic changes result in more frequent and intense storm events (IEG, 2007; Christensen and others, 2007), the need for mapping geologic hazards, such as landslides, becomes increasingly urgent. Hazards mapping is the basis for good growth management planning that can greatly reduce impacts to infrastructure and loss of life and property. Anecdotal evidence indicates that in Washington State, landslides account for at least several tens to hundreds of millions of dollars in economic losses per year. In 1998, the Aldercrest–Banyon landslide in Kelso, Washington, alone damaged or destroyed 138 homes and accounted for $30 to $40 million in losses (Wegmann, 2006). Nationally, landslides account for more than $2 billion in losses annually and result in an estimated 25 to 50 deaths a year (Spiker and Gori, 2003; Schuster and Highland, 2001; Schuster, 1996).
In order to mitigate such losses during future catastrophic landslide events, it is crucial to understand where and why slope failures and flooding occur. The time to accomplish such documentation is as soon after the event as possible, because the data are perishable. Landslides are quickly removed from roads and often stabilized or otherwise modified, destroying or obscuring critical data used to analyze the triggers for slope failures. If left too long, landslides become obscured or modified by weathering, erosion, and vegetation growth. Data recovered from landslide studies are essential to understanding hazards and associated risks, which greatly aids in identifying susceptible communities, speeding up emergency response, and helping state, county, and city officials mitigate against potential property damage and loss of life.
Landslide data for Washington State is most easily accessed by the Washington Geological Survey’s ArcIMS site, located here
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