Mount Rainier is a beautiful, world-renowned magnet for lovers of the outdoors and tourists who want a wilderness experience. Now there’s another reminder of its potential dark side, too.
A new report from the state Department of Natural Resources (DNR) estimates that a volcanic mudflow – a lahar – spewing from the mountain could cause property damage and losses of up to $6 billion to communities in the Puyallup Valley portion of Pierce County.
“We now have a much better estimate of the economic impact of a major lahar flowing from Mount Rainier,” which is an active volcano even though its last eruption was hundreds of years ago, said Dave Norman, a state geologist and manager of DNR’s Geology and Earth Resources Division. “It’s not a question of if, but when, the next volcanic event will occur.”
Lahars, which can be touched off by an eruption of lava or hot gasses that melt a glacier, or by avalanches and earthquakes, can push mud and debris at a high speed. The flow has the consistency of wet concrete.
Mount Rainier has produced major lahars every 500 to 1,000 years and smaller flows more frequently. The most recent big lahar to reach the Puget Sound region’s lowlands was what historians call the Electron mudflow, which happened about 600 years ago. The flow was more than 100 feet thick in the area now known as Electron and about 20 feet thick in what today is Orting.
The federal funded DNR report, titled “Loss Estimation Pilot Project for Lahar Hazards from Mount Rainier, Washington,” is based on research of previous lahars. 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 on the upper west flank of the mountain, the Puyallup Valley is the area considered most susceptible to lahars. Lahar-related flooding has the potential to reach Commencement Bay in Tacoma and Elliott Bay in Seattle, including the ports in both locations.
Besides the Puyallup, 10 other river valleys are considered hazard zones for lahars, lava flows and pyroclastic flows in the event of a major eruption. The valley drainages include the Nisqually River, with Alder Lake and the Elbe area along the way and Eatonville nearby, and – in Lewis County to the south – the Cowlitz River and Riffe Lake. All the areas could be “inundated” if eruptive events were similar to those in the past, the DNR report states..It alsol notes that the hazard from lahars isn’t equal in all the valleys. Experts say at least 60 lahars have traveled as far as 70 miles downstream. To go with the report released June 6, DNR has produced an online interactive map that simulates the potential pathways of lahars from Mount Rainier. Officials said the map and report are designed to help plan emergency responses and communities’ preparation for lahar-prone areas.
The study was paid for through the federal American Recovery and Reinvestment Act. The resulting report is available at DNR’s web site (www.dnr.wa.gov).
According to the U.S. Geological Survey (USGS), an eruption of Mount Rainier would probably be preceded by weeks or months of small earthquakes centered beneath the volcano, by subtle changes in the volcano’s shape, and by increases in volcanic gas emissions and temperatures. Those signals would people living communities in the path of eruptions to take precautions against lahars and evacuate if necessary.
USGS officials say scientists recognize that lahars, like the Electron mudflow, can occur when there are no eruptions, too. That has led to the installion of equipment that detects more subtle ground movements and a system that detects lahars and sends out warnings before they reach populated areas.