DNR Report: Mount Rainier lahar destruction could reach $6B in Puyallup Valley

A new report from the Washington State Department of Natural Resources (DNR) estimates that a volcanic mudflow (known as a ‘lahar’) from Mount Rainier could produce property losses of up to $6 billion to communities in the Puyallup Valley.

“We now have a much better estimate of the economic impact of a major lahar flowing


from Mount Rainier,” said Dave Norman, Washington State Geologist and manager of the DNR Geology and Earth Resources Division.” It’s not a question of if, but when, the next volcanic event will occur.”

The DNR report, “Loss Estimation Pilot Project for Lahar Hazards from Mount Rainier, Washington,” is based on data about several previous lahars from the volcano. It is available online here. Using loss-estimating software developed by the Federal Emergency Management Agency (FEMA), the report projects potential property damage costs if similar mudflows occurred again on Mount Rainier’s west side, as many geologists anticipate. Due to the weakened rocks that make up the upper west flank of Mount Rainier, the Puyallup Valley is considered highly susceptible to lahars. Lahar-related flooding has the potential to reach as far as the Commencement Bay and Elliott Bay, including the ports of Seattle and Tacoma.

In concert with the report released today, DNR has produced an online interactive map that allows users to track the potential pathways of lahars from Mount Rainier. The online map and today’s report are designed to assist emergency response, mitigation planning, and community preparation for lahar-prone areas.

Mount Rainier has produced major lahars every 500 to 1,000 years and smaller flows more frequently. The most recent major lahar to reach the Puget Lowland was the Electron Mudflow about 600 years ago. It was more than 100 feet thick at the community of Electron and as much as 20 feet thick at Orting.

Lahars, which have the consistency of wet concrete, can be caused by volcanic activity when an eruption of lava or hot gasses melts a glacier. They also can be produced by avalanches and earthquakes.

The DNR study was funded by the American Recovery and Reinvestment Act.