Landslides occur every year in Washington State—our climate, topography, and geology create a perfect setting for landslides.
So we highlight earth sciences as we move into fall and winter weather—one of the times that landslides commonly occur. DNR’s geologists in the Division of Geology and Earth Resources map landslides, maintain a database of more than 50,000 landslides, and study the characteristics that increase the potential of landslides in areas across the state. These scientists are developing information and maps that help state, county, and cities planners to avoid constructing or approving permits for buildings or roads in areas that may be prone to slides. These landslides can be accessed through our interactive map site.
DNR geologists also teach and work with public and private parties, and work closely as partners with other scientists at the US Geological Survey, NOAA (National Weather Service), University of Washington, and around the world.
In Western Washington, the majority of landslides are triggered during fall and winter, when we experience most of our large rainstorms. Losses from landslides are difficult to track, but conservative estimates of average losses over the last 30 years are more than $20 million per year. Nationally, landslides account for more than $2 billion in losses annually and result in an estimated 25-to-50 deaths a year.
Types of slides and their triggers
Shallow landslides generally occur quickly, during days of precipitation, and they tend to occur over a short time period— an example would be the debris flows that occurred after days of very hard rain in January of 2009.
Deep seated landslides generally are slow moving, and involve the effects of years of rain and water working through the landscape. These landslides generally display movement of earth over a long time period.
And landslides tend to occur in areas where there are geologic hazards. There is a long history of earthquakes triggering landslides in Washington State. Probably the most well known in Washington State are the Ribbon Cliffs landslide about 3 miles north of Entiat. It is thought that the Bonneville Landslide in Skamania County also may have been caused by an earthquake. Landslide movement into water can create tsunamis, such as has been speculated in the Alderwood Landslide. Volcanic activities and growth can result in instability on the flank of the volcano, resulting in extremely large landslides, such as Mt. St. Helens.
These scientists illustrate that the more we learn, the more we can help prevent disastrous placement of homes, businesses, roads and other public infrastructure.
You can help DNR map landslides… How do I report a landslide
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