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State geologists warn of increased landslide risk following Western Washington wildfires

A helicopter flies over fires burning on a ridge in Sumner, Wash., Wednesday, Sept. 9, 2020.
Rachel La Corte
The Associated Press
A helicopter flies over fires burning on a ridge in Sumner, Wash., Wednesday, Sept. 9, 2020.

Another potentially devastating effect of wildfires: increased landslide risk. The state Department of Natural Resources has a team doing rapid response analysis in areas that have recently burned.

Trevor Contreras, a geologist with the agency, says we have a bit of a grace period before heavy rains hit.

“Typically, it's the large convective thunder storms that cause intense precipitation and have the type of flooding that we're really concerned about,” he said.

Contreras is one of five state geologists doing analysis of potential slide areas after wildfires.

Right now, the team is focused on the Pearl Hill and Palmer Fires in north-central Washington. The team also will take a close look at how the recent brush fires in Pierce County changed

landscapes, especially around state Route 410.

State geologists use LIDAR and other geological data to assess risk and make recommendations to communities and emergency managers.

“Wildfires basically remove all the vegetation and make kind of a water-resistant, oily,

waxy surface under the soil that makes any water kind of run off immediately,” Contreras said.

He says his colleagues are working to educate homeowners and communities to see potential hazards and prepare for them. He says many people build on hillsides, thinking they’re way above the flood plain. 

“But a lot of times, that small creek can go from a trickle to a big flood hazard

after a fire,” Contreras said.

Since flood risk often increases after a fire, it’s a good time to check your insurance policy to make sure you’re covered, and start talking with local emergency managers about evacuation plans, if warranted.