King County is vulnerable to landslides due to our region's geography. In a landslide, large masses of rock, soil, and other debris move quickly down a slope. They can flow quickly, and occur with little or no notice. Landslides can also travel many miles from their source, growing in size as they pick up more mud and debris. Small landslides are reported every year in King County, blocking roads and sometimes causing damage to homes and other structures. The last large landslide in Washington state happened in March 2014 near the town of Oso in Snohomish County. 43 people lost their lives in that disaster.
Landslides can be caused by storms, earthquakes, and volcanic eruptions, or as a result of fires or human modification of land. The best way to prepare for a landslide is to stay informed about changes in and around your home that could signal that a landslide is likely to occur.
Due to King County's high population density and the fact that many structures are built on top of or below bluffs and slopes subject to landslides, many lives are endangered during these land movements. Understanding the possibility of a landslide in your area is an essential component to your family's emergency plan. More information is available from the U.S. Geological Survey (USGS).
In October 2019, the USGS unveiled a new web-based interactive map that marks an important step toward mapping areas that could be at higher risk for future landslides. In collaboration with state geological surveys and other federal agencies, USGS has compiled much of the existing landslide data into a searchable, web-based interactive map called the U.S. Landslide Inventory Map.
- Get a ground assessment of your property. Your city or county geologist or planning department may have specific information on areas vulnerable to landslides.
- Seek advice of geotechnical experts for evaluating landslide hazards or designing corrective techniques to reduce landslide risk.
- Plant ground cover on slopes to stabilized the land and build retaining walls.
- Plan at least two evacuation routes since roads may become blocked or closed.
- Learn to recognize the landslide warning signs:
- Doors or windows stick or jam for the first time.
- New cracks appear in plaster, tile, brick or foundation.
- Outside walls, walks, or stairs begin pulling away from the building.
- Slowly developing, widening cracks appear on the ground or on paved areas such as streets or driveways.
- Underground utility lines break.
- Bulging ground appears at the base of a slope.
- Water breaks through the ground surface in new locations.
- Fences, retaining walls, utility poles, or trees tilt or move.
- You hear a faint rumbling sound that increases in volume as the landslide nears. The ground slopes downward in one specific direction and may begin shifting that direction under your feet.
- Sinkholes - a sinkhole occurs when groundwater dissolves a vulnerable land surface, such as limestone, causing the land surface to collapse from a lack of support.
- Make arrangements for housing in the event you need to evacuate your home.
- Plan for earthquakes and severe storms that can trigger a landslide.
- If inside a building, stay inside. Take cover under a desk, table, or other piece of sturdy furniture.
- If outdoors:
- Try to get out of the path of the landslide or mudflow.
- Run to the nearest high ground in a direction away from the path.
- If rocks and other debris are approaching, run for the nearest shelter such as a group of trees or a building.
- If escape is not possible, curl into a tight ball and protect your head.
- Remember that flooding may occur after a mudflow or landslide.
- Stay away from the slide area. There may be danger of additional slides.
- Once it's safe, check for injured and trapped persons near the slide area. Remember to help neighbors who may require special assistance.
- Listen to local media or NOAA Weather Radio for current information.
- Check for damaged utility lines. Report any damage to your utility company.
- Check the building foundation, chimney, and surrounding land for damage.