Heavy rains can raise landslide risks

debris slideThe National Weather Service is predicting heavy rainfall across much of western Washington, including the Cascade Mountains, today through Friday afternoon. Amounts could range from one-inch in the lowlands to three inches or more in the foothills and mountains. Such intense rainfall in a short period of time could cause mud or rock slides as well as flooding.

Here in Washington, a combination of climate, topography, and geology creates a perfect setting for landslides. In western Washington, most landslides happen when we get heavy rainfall. Are you prepared? The Washington Emergency Management Division has useful information to help you prepare for natural hazards of all types, including storms, flooding and landslides.

Here are some the common warning signs of an impending mud or rock slide (the fast-moving, ‘shallow’ landslide that can be caused by heavy rains):

  • Sudden decrease in creek water levels, especially during storms
  • Sudden increase in creek water levels, often with increased sediment in the water
  • Sounds of cracking wood, knocking boulders, or groaning of the surrounding ground, or unusual sounds, like the sound of an oncoming freight train, especially if the sound increases
  • A hillside that has increasing springs, seeps, or saturated ground, especially if it has been dry
  • Formation of cracks or tilting of trees, especially evergreens, on a hillside

One of the most effective things you can do to keep safe in landslide country during landslide ‘weather’ is to know where landslides have occurred in the past. DNR’s Geology and Earth Resources Division collects landslide data to help increase understanding of landslide processes in Washington state. Take a look at our growing database on the Washington State Geologic Information Portal.

Check out our factsheet about landslide hazards Washington state.


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