Many people remember the eruption of Mt. St. Helens in 1980. So which volcano in the Pacific Northwest is the next to watch? And what would happen in the Mid-Valley if that eruption is close by?
The nearest active volcanic complex to Corvallis is the Three Sisters. Experts say that volcanic activity is possible – even overdue – for Mount Hood, Mount Saint Helens, the Three Sisters complex, Mount Bachelor, and the Newberry Crater areas.
The Mount St. Helens Precedent
The eruption of Mount St. Helens remains the most destructive and deadly volcanic event in United States history. It killed 57 people and thousands of animals. It destroyed 200 homes, 47 bridges, 15 miles of railway, and 185 miles of highway. And it created Coldwater Lake after debris blocked the flow of a river.
Prior to its eruption, injections of magma immediately beneath the volcano caused St. Helens to vent steam and rumble with earthquakes. The pressure caused a fracture system to build on the north slope. At 8:30 a.m. on Sunday, May 18, 1980, the entire north side of the mountain fell away. It was the largest landslide in Earth’s recorded history – 600 feet tall at its highest point – and it traveled 14 miles going between 70 and 150 miles per hour. A cloud of super-heated volcanic material shot 15 miles into the air and deposited ash in 11 states. Glaciers melted and formed lahars – boiling mudslides – that traveled nearly 50 miles.
As Spirit Lake filled with debris, the water level rose by 200 feet and deposited a variety of nutrient-rich lake materials into the surrounding earth, which returned to life with shocking vibrancy. Years after the eruption, the descendants of high-altitude fish were found in Spirit Lake, having been whisked from the glacier lakes with the force of the explosion.
What Would Happen in Corvallis?
Although the mountains may seem distant, their volcanoes pose a threat to the area in terms of ash deposits.
David Busby of the Corvallis Fire Department said that the ash “would immediately impact transportation area-wide, load up on roofing, and impact heating and air conditioning systems.”
The day Mount St. Helens erupted, ash descended like a blanket across Washington and Oregon. It blocked the sun, activated streetlights, piled up on outdoor surfaces, and made driving near-impossible as car tires stirred the deposited ash into blizzard-like clouds.
At first, ash is soft and amenable to the wind. With the addition of water, it hardens into a crust, becoming significantly harder to remove. And while floating ash appears weightless, a well-supported roof may collapse under less than five inches of buildup. Overhangs, gutters, and low-pitched or poorly-supported roofs may collapse under much less.
Corvallis is unlikely to see this amount of ash from a faraway eruption, but the city is still vulnerable to ash in other ways – its small, abrasive particles enter machinery of all kinds and cause microscopic, metallic abrasions, degrade hydraulic seals, reduce the effectiveness of car brakes, and clog filtration systems. Heating and air conditioning units with clogged filtration will ultimately overheat and fail.
And that’s to say nothing of its effects on our bodies. Sufficiently small ash particles – under 4 µm – can penetrate the alveolar tissues and cause chronic lung disease, like silicosis, which is associated with the inhalation of microscopic silica particles. Larger ash particles may cause acute irritation in the throat and eyes.
Beyond the ash, volcanoes pose a threat to glaciers; a volcanic eruption in Mount Hood or the Three Sisters complex could disrupt or completely destroy the peaks’ many glaciers, which support the valley water supply by stabilizing the snowpack. If the glaciers were to vaporize in an eruption, Corvallis’ water supply may be threatened.
Is Corvallis Prepared?
There are a number of alert systems to inform residents of possible safety issues, like the statewide Oregon Alert and the federal Wireless Emergency Alerts. The Sheriff’s Offices in both Linn and Benton County use the Linn-Benton Alert system to warn residents of safety issues, and Corvallis uses the Corvallis Alert.
Busby said that the county and the city would together activate an Emergency Operations Centers. “That is both county and city staff working together to collect and distribute information, identify impacts to the community, and coordinate response efforts and resources to support the whole community.”
He added, “We have already done this for the pandemic and 2020 wildfires, and it is a great team effort.”
To qualify for disaster funding, states are required to develop and maintain plans for natural hazard mitigation. In 2016, the Benton County Board of Commissioners adopted the latest Benton County Natural Hazard Mitigation Plan. In late 2021, the county issued a progress report, available here.
The plan assesses natural hazards in terms of probability and vulnerability. A Cascadia earthquake ranks highest with a moderate probability and high vulnerability, while wildfire and winter storms rank in the middle with high probability and low vulnerability. Volcanoes rank lowest with a moderate probability and low vulnerability.
According to the plan, “moderate” probability means that one incident is likely within the next 75 years. “Low” vulnerability means that less than 1% of the region’s population or assets would be affected. But for that 1%, the effects could be deadly.
In the event of a volcano, Corvallis residents should be prepared to shut off ventilation systems and shelter in place for a period of time. Residents may consider maintaining an independent supply of food, water, masks, medical supplies, clean clothing, air filters, and other insulation materials in the event that utilities and deliveries are disrupted.
Will There be Warning?
It’s possible that the 1980 St. Helens eruption will render future eruptions especially explosive, with significantly less material to slow the expulsion of lava.
“If I were to put my money on a volcano erupting,” says Leif Karlstrom, volcanologist at OSU, “I’d put it on Mt. St. Helens.”
Scientists also recently detected new movement in the Three Sisters complex, southwest of Corvallis. According to Jon Major and his team at the Cascades Volcano Observatory, the ground is moving measurably upward as magma moves deep under the ground, exerting pressure on the upper crust and causing tiny earthquakes.
According to Major, the earthquakes are “well below magnitude 1.”
The current uplift is faster than what his team has measured in the past two decades, occurring along a 12-mile stretch, but this isn’t necessarily cause for concern. Major said that “this process has probably been going on for a long time, but we haven’t necessarily had the technology to detect this kind of thing before.”
He explained that an impending eruption would likely cause more uproar.
“There would be a lot more signs that magma was making its way to the surface and poised for an eruption,” said Major.
In a world increasingly affected by climate change, volcanoes and earthquakes may be the last of Oregonians’ worries. But with the grand-daddy of all volcanoes in our attic, it doesn’t hurt to be aware.
By Grace Miller
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