Areas of the White Salmon River valley that could be inundated by a future lahar, ranging in volume from 1 million (dark red) to 1 billion (yellow) cubic meters, rushing down from Mount Adams. Fast-moving slurries of weakened rock, water and other debris, geologists can’t predict the size of potential lahars.
TROUT LAKE — In September, scientists recorded six low-intensity earthquakes beneath Mount Adams, marking the 12,276-foot volcano’s most seismically active month since monitoring began in 1982, and the United States Geological Survey Cascades Volcano Observatory (CVO) detected more in October.
With magnitudes ranging from 0.9 to 2.0, the earthquakes didn’t produce any visible shaking. Tom Pierson, a research geologist and hydrologist who retired from CVO in 2018, affirmed there’s no imminent eruption threat, and in response, CVO has already installed three more temporary seismic monitoring stations near Mount Adams.
“Being able to pinpoint where these quakes are happening down to the immediate location of the volcano would really help,” said Pierson. Increased seismic activity could result from magma movement within Mount Adams, or shifting tectonic plates throughout the broader Cascadia subduction zone.
CVO has not yet identified the cause. In October, the observatory recorded one earthquake at the original station, but the temporary sites have picked up one or two extremely small earthquakes every day. For context, Mount Adams used to only see one earthquake every two or three years, but now CVO has the equipment and sensitivity to detect more.
While increased seismic activity does suggest that a volcano might be “waking up,” CVO looks for other indicators like ground deformation and a surge in gas emissions. Even though the observatory doesn’t have a gas sensing station on Mount Adams, Pierson reported there’s no sign of either. Since these factors aren’t present, and Mount Adams isn’t producing hundreds of earthquakes per week, the risk level remains normal.
“If it were going to erupt to the surface, it would have to build up enough volume in the magma chamber, and that takes time,” said Pierson. “We would expect a buildup of probably months to a year or two before that would cause people to think an eruption is going to happen.”
Areas of the White Salmon River valley that could be inundated by a future lahar, ranging in volume from 1 million (dark red) to 1 billion (yellow) cubic meters, rushing down from Mount Adams. Fast-moving slurries of weakened rock, water and other debris, geologists can’t predict the size of potential lahars.
Columbia Gorge News file photo
Hypothetically, a Mount Adams eruption would also look quite different compared to Mount St. Helens, when the north side blew completely off in 1980. Mount Adams doesn’t have an explosive history; rather, it’s an effusive volcano that produces thick, sticky lava flows without the cloud of ash. The real danger is lahars, volcanic mudflows combined with melted glacial ice and rocks that can rush down river valleys.
“Mount Adams is raised really high up into the air, and that rock has been subjected to hundreds of thousands of years of gases, very acidic gasses,” said Pierson. Those gases creep through cracks in the rock and cause chemical reactions that effectively weaken it, as Pierson explained. These liquid landslides can be triggered by an eruption, earthquakes, rapid snowmelt or further erosion.
About 6,000 years ago, a lahar from Mount Adams buried the entire White Salmon River valley, inadvertently damming Trout Lake Creek to form Trout Lake, and a smaller lahar approached the town just over 260 years ago. Pierson noted there’s a large patch of weakened rock on the southwest flank of Mount Adams, near the summit, and a smaller eastern patch aimed toward the Klickitat River.
“The probability of a lahar occurring is very low currently,” said Pierson. “If they hear low-frequency rumbling sounds coming from that direction, we advise folks to get to high ground as soon as possible.” A lahar could reach Trout Lake in only 15-20 minutes, so CVO is actively working on establishing an early warning system.
Again, the latest risk level at Mount Adams is normal. If you wish to receive updates on volcanic activity, visit volcanoes.usgs.gov/vns2/subscribe.
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