For many, the word “eruption” brings to mind 1980 when Mount Saint Helens demonstrated that the Washington Cascades are one of the most volcanically active parts of the country.
Mount Saint Helens, Mount Adams, Mount Baker, and Glacier Peak are four of the active volcanoes in Washington state. The fifth, located less than 70 miles from Seattle, is Mount Rainier.
“It’s totally at a state of background activity, so we’re not worried about Mount Rainier right now,” said Alex Iezzi, a research geophysicist with the U.S. Geological Survey.
Iezzi’s team with the USGS Cascades Volcano Observatory monitors the Cascades daily. Their infrasound and seismic sensors detect cracks and movement from below as magma is forced upward. Gas sensors signal changes in volcanic fumes, and GPS sensors monitor and measure ground deformation.
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With researchers monitoring Mount Rainier so closely, Iezzi said if a big eruption were to occur, it’s likely “we would be able to see it for months in advance.”
Such an eruption, with certain prevailing winds, may be able to bring volcanic ash to Seattle. However, lava flow or mudflow impacting the Seattle area would be very unlikely. But in cities closer to the foothills, like Puyallup and Orting, there are serious hazards.
In 2018 the USGS updated its assessment of the most dangerous volcanoes in the United States, ranking Mount Rainier third on the list behind Mount St. Helens and Hawaii’s Kilauea. The USGS said Mount Rainier was ranked third due to its history of large, destructive eruptions and its proximity to heavily populated areas. Experts believe an eruption from Mount Rainier would post a grave threat to millions of people who live in the southern and eastern sections of the Seattle metropolitan area.
“One of the main hazards at Rainier, is it’s less explosive, but it has a lot of glaciers on top of it that can melt and form these really large lahars that can move downstream into areas people live in,” Iezzi said.
Lahars are very destructive volcanic mudflows that can swallow everything in their paths. During the Mount St. Helens eruptions, lahars flowed up to 60 miles destroying 200 homes. Lahars are one of the risks with a Mount Rainier eruption, so many foothill communities prepare.
“There’s a lahar evacuation drill in the areas of Orting and Puyallup (and every year or two), and I think 45,000 people participated this year,” Iezzi said.
In isolated incidences, lahars can trigger without a volcanic eruption from a landslide instead. These so-called “no notice lahars” are the reason extra sensors are concentrated in drainage areas on the southwest slopes of Mount Rainier.
Iezzi said in the Cascades, wind patterns would often direct any ash from an erupting volcano eastward whereas the lahar risk primarily impacts the western slopes. And while Mount Rainier hasn’t erupted in 1,000 years, the team with the USGS will be watching for when it shows the signs.
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