Heavy rains often cause localized flooding and higher river levels, but prolonged, intense rain like that sweeping western Washington this weekend increases the chances of shallow landslides.
In any given year, Washington can see hundreds, if not thousands of landslides.
Rainwater can infiltrate the ground, causing western Washington’s porous, sandier topsoil to weaken and slide off a base of firmer, impermeable clay. The steepness of eastern Washington slopes are also vulnerable to landslides. (Timothy Walsh, DNR Chief Hazards Geologist, explains in this video.)
In an effort to give communities a rating of how rainfall may increase the threat of landslides, Washington State Department of Natural Resources has teamed up with the National Weather Service to provide a map showing the risk of shallow landslides.
Updated every morning, the Shallow Landslide Hazard Map uses rainfall data from the previous 48 hours along with the Weather Service’s forecast rainfall for the next 24 hours to determine how high the hazard might be.
The map does not predict landslides at any particular time or location, but is intended to raise awareness of shallow landslide hazards caused by periods of prolonged rainfall. Landslides may occur in counties that have a low hazard rating and may not occur in all or any areas at high hazard
It is still in beta mode, so timely delivery of data is not guaranteed.
Warning signs of an impending landslide
If you live on or near a steep slope, here are some warning signs of potential slope instability:
- Cracks forming in your yard, driveway, sidewalk, foundation or in other structures.
- Trees on slopes, especially evergreens, start tilting.
- Doors and windows suddenly become more difficult to open or close.
- Water begins seeping from hillsides, even during dry weather.
If you see any of these early signs of a potential landslide, immediately contact your city or county.
- Map of Washington State Emergency Contacts
- DNR landslide fact sheet
- DNR Natural Hazards online interactive map
- Washington Department of Ecology Puget Sound Landslides page
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