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March 3, 2024

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A lahar on Mount Adams would put thousands at risk but monitoring stations would warn of dangerous flows

“We’ve been through major wildfires, but there’s something about the lahar that feels ultimately more fatal,” says resident

By , Columbian staff writer
8 Photos
Pat Arnold points to boulders that were presumably carried from Mount Adams&rsquo; Trout Lake mudflow 6,000 years ago. &ldquo;A strong force must have moved those downward,&rdquo; she said.
Pat Arnold points to boulders that were presumably carried from Mount Adams’ Trout Lake mudflow 6,000 years ago. “A strong force must have moved those downward,” she said. (Taylor Balkom/The Columbian) Photo Gallery

TROUT LAKE — As Pat Arnold plucked weeds from her yard with a view of snow-capped Mount Adams, she navigated around large boulders that hint at the volcano’s destructive past.

Over the course of thousands of years, the volcano several times has sloughed rocky debris like the rocky mounds in Arnold’s yard. It doesn’t take a volcanic eruption to unleash these lahars, forceful slurries of mud, rock and debris. Although lahars aren’t explosive, they can be catastrophic.

And they aren’t just ancient history. In fact, geologists expect them to happen again, threatening the thousands of people who live on Mount Adams’ flanks. That’s why the U.S. Geological Survey’s Cascade Volcano Observatory is working on a warning system to give them time to escape.

“There’s no imminent threat at Mount Adams that we’re aware of now. That’s not to say it couldn’t happen tomorrow,” said Jon Major, the observatory’s scientist-in-charge. “We can’t say with any degree of certainty that it is going to happen tomorrow, 100 years from now or 1,000.”

A large patch of rock at Mount Adams’ upper cone is physically weak, the result of years of cold and hot water circulating through minerals, he said. The weathered mass of rotten rock — sitting thousands of feet above Trout Lake — remains under the influence of gravity, ready to tumble with an earthquake or further erosion.

The 1980 Mount St. Helens eruption unleashed the region’s most recent and destructive lahar. More than 2 billion cubic yards of material wiped out bridges and buried forests across the upper 17 miles of the North Fork Toutle River valley, according to USGS. However, an eruption isn’t necessary to set off a lahar. These liquid landslides can be triggered by erosion and rapid snowmelt.

A lahar can grow more than 10 times its original volume as debris rushes downhill. Depending on the steepness of a slope, lahars can surpass 120 mph before slowing in lowland areas, burying everything in their path.

Once Arnold learned about the geological threat at her doorstep, she began making a plan. She said she would have to abandon her multiple chickens, barn cats and donkeys, Minnie and Pearl. She wouldn’t have much time because Mount Adams would already be closing in. If she had the 15-minute warning that could come with the planned USGS detection system, she would scoop up her elderly beagle and drive to a hill nearby, from which she would watch water and debris swallow her property.

“We’ve been through major wildfires, but there’s something about the lahar that feels ultimately more fatal,” she said, glancing behind her at the snow-capped peak.


Multiple 3-by-5-foot aluminum boxes hold the solution for saving communities nestled within Mount Adams’ hazard zone, including Trout Lake, BZ Corner and Husum.

Ben Pauk, a geophysicist leading the monitoring project, poked at a prototype’s contents — multicolored wires, infrasound sensors and GPS receivers. The instruments are like a trip wire that detects ground movement and, if fitted with a notification system operated by county and state agencies, pings those nearby.

From the time it’s detected, a lahar could flow down the White Salmon River valley and reach Trout Lake within 20 minutes, Pauk said.

Glossary of Terms

Lahar: A hot or cold mix of water and rock that quickly flows down a volcano’s slope.

Stratovolcano: A steep, cone-shaped volcano built from eruptions of lava and pyroclastic flows.

Pyroclastic flow: A quick-moving, hot mix of rock, gas and ash.

Jeff King, Klickitat County emergency management director, said the system would notify the county’s emergency officials so they can respond. How they would respond — that’s something they’re just now figuring out.

The Klickitat County Emergency Plan, which applies to Trout Lake, doesn’t have a section on lahars, even though geologists know they have historically swept through the valley. Trout Lake’s emergency handbook outlines recommendations for general preparedness and evacuation routes, but so far includes nothing specific to lahars, except for a brief definition.

The aluminum box and its insides, as well as solar panels for charging, are compact and can be transported in the back of a truck to most sites. Each system — five are proposed — can be “put together like a Tinker Toy,” Pauk said.

Most of the Cascades’ volcanoes have robust systems to monitor lahars, but Mount Adams is among the few that don’t, Major said.

Although Mount Adams is toward the bottom of geologists’ lists, the volcano is still considered a threat that warrants close monitoring.

The USGS plans to scatter stations around Mount Adams, but it can’t put them inside the Gifford Pinchot National Forest’s wilderness boundaries lest they interfere with wildlife habitat or archaeological sites. That pushes them farther from Mount Adams. The stations’ distance from the peak will result in a lag between the onset of a lahar and when those in the valley are notified, Pauk said.

Once the U.S. Forest Service issues permits and the snow melts in the spring, USGS will install the new stations.

A long time coming

Mount Adams’ steep and pointed shape tells the tale of its long, eruptive past. Its layers of lava, ash and rock are typical of a stratovolcano.

The grooves carved in the White Salmon drainage also tell the story of massive avalanches of clay and other debris that swept through the valley.

About 6,000 years ago, the Trout Lake mudflow dammed Trout Lake Creek, forming the titular lake, and scattered large boulders throughout the flat landscape. And 300 years ago, another large flow, the Salt Creek lahar, scoured the valley. These massive lahars deposited the material that underlies Trout Lake.

Significantly smaller lahars of snow and ice continued to fall down Mount Adams’ flank. The USGS observed one as recently as 2017, according to a 2018 report. Although these smaller flows didn’t reach the Trout Lake valley, they are a reminder that rock on the volcano’s steep cliffs is unstable.

“We might not have any precursor earthquakes or volcanic activity,” Trout Lake resident Rachel Haymon said. “It could just happen.”

In the early 1990s, Haymon, a retired Earth science professor, and her husband, also a geologist, moved to a cabin on the Salt Creek lahar deposit. Curiosity drove them to investigate Mount Adams’ influence in shaping the valley. They were surprised to learn the volcano didn’t have a modern warning system like its neighbors, Mount Rainier and Mount St. Helens.

“We’re sitting here on Mount Adams going, ‘Well, we probably need that, too,’ ” she said. “If I don’t get that warning, I’m dead.”

By 2014, Haymon contacted the Cascades Volcano Observatory with her concerns — the impetus for the observatory’s current monitoring system project. She and former colleagues from University of California, Santa Barbara built temporary instruments, installed in 2017, as a “proof of concept” to show a system could be simple yet effective. They removed the equipment after three years.

The Cascades Volcano Observatory’s other priorities delayed implementation of a permanent monitoring system at Mount Adams, Major said.

“Putting instrumentation on the ground isn’t the end of it. That’s only the beginning,” he said. “It’s just one part of a much broader equation that has to be solved.”

Until this happens, Haymon continues to sound the alarm. Arnold said she didn’t know about the risk Mount Adams posed when she moved to Trout Lake in 1991. At least not until she befriended Haymon.

Residents in communities surrounding Mount Adams sit within a hazard zone, and many seem unaware of the volcano’s threat, Haymon said. A lahar’s damage isn’t preventable, but USGS’s monitoring system and county’s alert system can minimize loss.

“Some people might still not escape,” Haymon said. “But you can save a lot of people.”

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This story was made possible by Community Funded Journalism, a project from The Columbian and the Local Media Foundation. Top donors include the Ed and Dollie Lynch Fund, Patricia, David and Jacob Nierenberg, Connie and Lee Kearney, Steve and Jan Oliva, The Cowlitz Tribal Foundation and the Mason E. Nolan Charitable Fund. The Columbian controls all content. For more information, visit columbian.com/cfj.

Columbian staff writer