Distant volcanoes pose a risk to Corvallis

Many people remember the eruption of Mount St. Helens in 1980. So which volcano in the Pacific Northwest is next to watch? And what would happen in Mid-Valley if this eruption were near?

The closest active volcanic complex to Corvallis is that of the Three Sisters. Experts say volcanic activity is possible — even overdue — for Mount Hood, Mount St. Helens, the Three Sisters Complex, Mount Bachelor, and Newberry Crater regions.

The precedent of Mount St. Helens

The eruption of Mount St. Helens remains the most destructive and deadliest volcanic event in United States history. It killed 57 people and thousands of animals. It destroyed 200 homes, 47 bridges, 15 miles of railroad and 185 miles of highway. And he created Coldwater Lake after debris blocked the flow of a river.

Prior to its eruption, injections of magma immediately beneath the volcano caused steam to vent and earthquakes to occur in St. Helens. The pressure caused the formation of a system of fractures on the northern slope. [Text Wrapping Break][Text Wrapping Break]At 8:30 a.m. on Sunday, May 18, 1980, the entire north side of the mountain collapsed. It was the largest landslide in Earth’s recorded history – 600 feet high at its highest point – and traveled 14 miles at between 70 and 150 miles per hour. [Text Wrapping Break][Text Wrapping Break]A cloud of superheated volcanic material was thrown 15 miles into the air and deposited ash in 11 states. The glaciers melted and formed lahars – boiling mudslides – which traveled nearly 80 kilometers.

As Spirit Lake filled with debris, the water level rose 200 feet and deposited a variety of nutrient-rich lake material into the surrounding land, which came alive with shocking vibrancy. Years after the eruption, the descendants of high-altitude fish were found at Spirit Lake, having been driven from glacial lakes by the force of the explosion.

What would happen in Corvallis?

Although the mountains may seem distant, their volcanoes pose a threat to the region in terms of ash deposition.

David Busby of the Corvallis Fire Department said the ash would “immediately impact transportation throughout the area, load onto the roof and impact heating and air conditioning systems”.

On the day Mount St. Helens erupted, ash descended like a blanket across Washington and Oregon. It blocked the sun, activated streetlights, piled up on exterior surfaces and made driving nearly impossible as car tires stirred up deposited ash into blizzard-like clouds.

At first, the ash is soft and ready for the wind. With the addition of water, it hardens into a crust, becoming much more difficult to remove. And while floating ash seems weightless, a well-supported roof can collapse under less than five inches of buildup. Overhangs, gutters, and low-pitched or poorly supported roofs can collapse under much less.

Corvallis is unlikely to see this amount of ash from a distant eruption, but the city is still vulnerable to ash in other ways – its small abrasive particles penetrate machinery of all kinds and cause microscopic metal abrasions, degrade hydraulic seals, reduce the effectiveness of car brakes and clog filtration systems. Heating and air conditioning units with clogged filtration will eventually overheat and fail.

And that’s not to mention its effects on our body. Small enough ash particles – less than 4 µm – can penetrate alveolar tissues and cause chronic lung diseases, such as silicosis, which is associated with inhalation of microscopic silica particles. Larger ash particles can cause severe throat and eye irritation.

Beyond the ash, volcanoes pose a threat to glaciers; a volcanic eruption at Mount Hood or the Three Sisters complex could disrupt or completely destroy the many summit glaciers, which support the valley’s water supply by stabilizing the snowpack. If the glaciers were to vaporize in an eruption, Corvallis’ water supply could be at risk.

Is Corvallis ready?

There are a number of alert systems to notify residents of potential safety issues, such as Oregon’s statewide alert and federal wireless emergency alerts. Linn and Benton county sheriff’s offices use the Linn-Benton Alert system to notify residents of safety issues, and Corvallis uses the Corvallis Alert.

Busby said the county and city will jointly activate an emergency operations center. “It’s county and city staff working together to collect and distribute information, identify community impacts, and coordinate response efforts and resources to support the entire community.”

He added: “We’ve done it before for the pandemic and the 2020 wildfires, and it’s a great team effort.”

To qualify for disaster financing, states are required to develop and maintain natural hazard mitigation plans. In 2016, the Benton County Board of Commissioners adopted the latest Benton County Natural Hazard Mitigation Plan. At the end of 2021, the county published a progress report, available here.

The plan assesses natural hazards in terms of probability and vulnerability. A Cascadia earthquake ranks first with moderate probability and high vulnerability, while wildfires and winter storms rank in the middle with high probability and low vulnerability. Volcanoes rank lowest with moderate likelihood and low vulnerability.

According to the plan, a “moderate” probability means that an incident is likely within the next 75 years. A “low” vulnerability means that less than 1% of the population or assets in the area would be affected. But for that 1%, the effects could be deadly.

In the event of a volcanic eruption, residents of Corvallis should be prepared to shut down ventilation systems and shelters 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 case utilities and deliveries are disrupted.

Will there be a warning?

It is possible that the 1980 St. Helens eruption will make future eruptions particularly explosive, with much less material to slow the expulsion of lava.

“If I had to put my money on an erupting volcano,” says OSU volcanologist Leif Karlstrom, “I would put it on Mount St. Helens.”

Scientists have also recently detected new movements in the Three Sisters complex, southwest of Corvallis. According to Jon Major and his team at the Cascades Volcano Observatory, the ground is measurably moving upward as magma moves deep beneath the ground, putting 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 over the past two decades, occurring over a 12-mile stretch, but that’s not necessarily cause for concern. Major said “this process has probably been going on for a long time, but we didn’t necessarily have 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 ready for an eruption.”

In a world increasingly affected by climate change, volcanoes and earthquakes could be the last worries for Oregonians. But with the grandfather of all volcanoes in our attic, it doesn’t hurt to be aware.

By Grace Miller

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