Mt. Adams has been in the news recently for unusual earthquake activity. We dive into the range where it resides, look back at Mt. St. Helens damaging 1980 explosion, and offer tips for how you can visit.
Seismic activity at Mt. Adams has been in the news recently. Although Mt. Adams is considered a “high threat” volcano by the USGS, it’s less worrisome than its “very high threat” sisters, Mt. St. Helens and Mt. Rainier. This week, we’ll travel to the Pacific Northwest to visit the Cascades and take a look.
Sharon Lyon
Editor, GeoLifestyle
Earthquakes at Mt. Adams
Mark A. Lee/Shutterstock.com
The Cascades comprise a long volcanic arc, stretching from northern California to British Columbia. They run parallel to the 700-mile-long Cascadia Subduction Zone, where the Juan de Fuca plate subducts below the North American plate. Mt. St. Helens is the most active of the Cascade volcanoes.
Located 37 miles east of Mt. St. Helens, Mt. Adams typically exhibits one earthquake every 1–2 years. BUT this year, there have been 10; six were recorded in September beneath this relatively calm volcano.
The big question: Do residents of the Yakama Indian Reservation, on which part of the mountain is situated, need to worry?
In comparison, Mt. St. Helens has somewhere between 10–20 earthquakes per month.
The earthquakes below Mt. Adams have been small—ranging from magnitudes of 0.9 to 2.0. None were felt at the surface.
Satellite imagery does not show any detectable ground deformation at the volcano.
The last lava known to have erupted from Mt. Adams is an approximately 1000-year-old flow from a side vent.
Just in case: Because only one seismic station is near the peak, scientists from the USGS and the U.S. Forest Service installed a new temporary seismic station at Mt. Adams. More are planned.
The bottom line: At this time, the USGS places the alert level and color code for Mt. Adams at GREEN/ NORMAL.
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Lava dome inside the Mt. St. Helens caldera, twenty years after the major eruption.
Mt. St. Helens erupted in 1980 in a fiery Plinian eruption that was not unexpected, but quite damaging, nonetheless.
Leading up to the explosion, large earthquakes and steam venting began two months prior. One month before the eruption, the north side of the mountain began to bulge.
On May 18, 1980, a 5.1-magnitude earthquake shook the mountain. The bulging north face of the volcano slid downhill in a massive avalanche of rock debris, slamming into Spirit Lake. A lateral explosion felled trees in a blast zone covering 150 square miles. A vertical explosion sent a column of ash thousands of feet into the air. The top 1,300 feet of the mountain was blown off.
Mud and debris mixed to form a lahar that flowed down the Toutle and Cowlitz Rivers, catching vacationers by surprise, taking out roads and bridges, and sweeping up timber from lumber yards. Fifty-seven people were killed.
Moving 60mph, the ash cloud turned day to night in Spokane and Yakima, Washington. Two days later, a diffuse ash cloud was detected on the East Coast.
The blast area: The eruption of Mt. St. Helens left a barren wasteland of downed and dead trees, volcanic blocks and bombs, pumice, and ash.
Felled trees cover 143 square miles, known as the blowdown zone. The trees are aligned so that you can follow the direction of the blast as it ricocheted off the opposite valley walls and other landforms in the way.
There are also 42 miles of still-standing dead trees, killed by the volcanic gases and rock fragments. This is known as the scorch zone.
Small mammals—shrews, deer mice, and chipmunks—survived the blast, although in greatly reduced numbers. Most of the 15 endemic species of frogs, toads, salamanders, and newts survived as well.
Forty years later, pocket gophers have dug hundreds of miles of tunnels in the blast area. Roosevelt elk and Columbia black-tailed deer forage on native plants and grass and clover planted for erosion control. The mountain goat, American black bear, and cougar have returned to the area.
Recovery efforts:
In the late 1980s, the first noticeable recovery took place in the NW quadrant of the blast zone, farthest from the volcano.
By the late 1990s, the terrain east of Spirit Lake was considerably greener.
The only area beyond the slopes of the mountain itself that appeared bare was the Pumice Plain by 2016. Ground surveys, however, found prairie lupine growing there.
Lasting impact:
In the years since the major eruption, several lava domes have formed inside the caldera, and plumes of steam and ash have occurred. Eruptions ceased in 2008.
The scale of the eruption and the beginning of reclamation in the Mt. St. Helens blast zone can be seen in NASA Landsat photos.
Visiting Mt. St. Helens National Volcanic Monument
Outcrop showing andesite/dacite composition of the igneous rocks, Mt. St. Helens. I'm standing in front for scale.
Trek on one of the trails, peruse the visitor centers, take a guided hike, and drive to the overlooks. But don’t be a pumice picker! You’re in a National Monument.
The Mt. St. Helens Institute offers guided hikes, including summit climbs and hikes into the crater. You can trek across the Pumice Plain or snowshoe during the winter.
Mt. St. Helens Visitor Center at Silver Lake is located about 30 miles west of the mountain. Exhibits include a large model of the volcano, a seismograph, a theater program, and an outdoor nature trail. Displays showcase the history and connection of the Cowlitz Indian Tribe to the mountain. The center closed Sept. 30 and will reopen in May 2025.
At the Forest Learning Center at Mt. St. Helens, located outside the blast zone, you can learn about forest recovery, reforestation, and conservation of forest resources.
When I was there, the Johnston Ridge Observatory was open, with a spectacular view, four miles from the mountain; however, a landslide in 2023 has closed access and it may not reopen until 2027.
Driving along Rt. 99, which skirts the east side of the mountain, allows for views of Spirit Lake and the Pumice Plain. Be forewarned, the road is very narrow, with steep drop-offs and few guardrails—a white-knuckle ride.
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