September saw an increase in earthquake activity at Mount Adams, according to the U.S. Geological Survey (USGS) Cascades Volcano Observatory and the Pacific Northwest Seismic Network.
A total of six earthquakes ranging between 0.9 and 2.0 in magnitude were recorded on a seismic station near the Cascade stratovolcano last month. Previously, the station only recorded one earthquake every two to three years, according to USGS.
“This represents the most earthquakes located at Mount Adams in a month since monitoring began in 1982. No earthquakes were felt at the surface,” USGS stated. “The locations and depths are not well constrained due to the sparse Mount Adams seismic network, and smaller earthquakes have occurred that seismologists have been unable to locate.”
The Mount Adams seismic network only has a single seismic station about 7 miles southwest from the stratovolcano’s peak.
With the sharp increase in earthquake activity, though, the USGS Cascades Volcano Observatory and the Pacific Northwest Seismic Network are installing more temporary seismic stations to the south and southwest of Mount Adams.
These additional seismic stations will allow them to better detect and pinpoint earthquakes in the area.
Despite the increase, the USGS volcano alert level for Mount Adams remains at its lowest level — green/normal — meaning the seismic activity observed is still considered typical background activity for an active volcano.
Aside from earthquakes, other background activity for the green/normal alert level includes steaming, thermal venting and other thermal features, none of which have been reported at Mount Adams. Satellite imagery shows no detectable ground deformation.
Degassing is another green/normal alert level activity; however, Mount Adams currently lacks a dedicated volcanic gas sampling program, according to the USGS news release. It is unknown whether or not the stratovolcano has vented gas recently.
A part of the Cascade Volcanic Arc, which includes Mount Rainier and Mount St. Helens among 16 other volcanoes stretching from northern California to British Columbia, Mount Adams is located around 50 miles southwest of Yakima and 30 miles north of the White Salmon-Hood River area along the Columbia River.
At 12,277 feet tall, it is the second tallest active volcano in Washington state behind Mount Rainier, and the largest in the state by area and volume. According to the USGS, Mount Adams last erupted between 3,800 and 7,600 years ago.
While currently at a green/normal volcanic alert level, the USGS still considers Mount Adams a high-threat volcano per its national volcanic threat assessment — the second highest level.
To learn more about Mount Adams and the recently observed seismic activity, read the USGS Cascades Volcano Observatory news release at https://bit.ly/47UpMNM.
As for earthquake activity at Mount Adams’ neighbors, the Pacific Northwest Seismic Network’s earthquake tracker reported Mount St. Helens had 77 earthquakes over the past 30 days while Mount Rainier had 16 over the last 30 days.
Despite more frequent earthquake activity, Mount Rainier is also at the USGS green/normal volcano alert level. But it is still considered the most likely volcano to erupt next in the Cascade Volcanic Arc and the most dangerous volcano in the nation.
Mount Rainier was named to the Decade Volcanoes list, which includes what are considered to be the 16 most dangerous active volcanoes in the world — due to both high eruption risk and proximity to densely populated areas — as identified by the International Association of Volcanology and Chemistry of the Earth’s Interior.
While Mount St. Helens had the most seismic activity in September, it is also the most recent in the Cascade Volcanic Arc to erupt, with its last major eruption occurring on May 18, 1980.
Both Mount Rainier and Mount St. Helens are considered very high-threat volcanoes according to the USGS national volcanic threat assessment — the highest level.
To view the Pacific Northwest Seismic Network’s seismic activity tracker, visit https://www.pnsn.org/volcanoes.
For more information on the USGS Cascades Volcano Observatory, visit https://www.usgs.gov/observatories/cvo.
For more information on the USGS’ volcano alert levels, visit https://www.usgs.gov/programs/VHP/alert-level-icons.
To read the most recent USGS national volcanic threat assessment conducted in 2018, visit https://pubs.usgs.gov/publication/sir20185140.
