They can be seen from almost anywhere in southern Washington: two snowcapped domes and a jagged crater rising above the stretches of forest beneath them, each isolated but all created by the same explosive forces. Mount Adams, Mount Rainier and Mount St. Helens are all icons of the skyline of the Pacific Northwest; geologically, however, each have been seen as fueled by different fiery sources.
But a controversial study released Oct. 25 suggests a massive body of molten rock may connect the solitary volcanoes deep underground, supplying magma to all three—a chamber that would be one of the largest in the world, similar in size to those under Yellowstone National Park and New Zealand.
The study, led by Graham Hill of the Institute of Geological & Nuclear Sciences and sponsored by GNS Science—New Zealand’s version of the U.S. Geological Survey (U.S.G.S.)
—began in 2006. This was during Mount St. Helens’ most recent eruption, and focused on a giant electromagnetic anomaly known as the Southern Washington Cascades Conductor.
Western geology professor Jackie Caplan-Auerbach said geologists have been aware of this area since the 1980s, and it has been extensively studied. The anomaly is detectable because magnetic and seismic waves travel slower in liquid than in solid rock. Caplan-Auerbach said the current theory is that the conductor is a body of water-loaded sedimentary rock.
Using a technique that measures electrical currents in the Earth’s magnetic field, the team could determine the conductivity of the earth’s crust as deep as 20 miles below ground.
Matt Burgess, a Western graduate and hydrologist who worked on the study, said researchers found the conductor seems to connect with Mount St. Helens’ known magma chamber, which is less than 10 kilometers under the mountain.
Researchers then headed east and began taking measurements toward Mount Adams. There they found, according to the study, a large, highly conductive zone beneath the mountain also connected to the Southern Washington Cascades Conductor.
A single measurement taken south of Mount Rainier suggests it too may be connected to the conductor. However, more measurements are needed before making that conclusion, according to the study.
Caplan-Auerbach said sedimentary rock loaded with water could explain the anomaly, but to study areas as deep as the conductor, geologists often rely on models.
The magma chamber theory is not new, she said, but is one of the more extreme models that have been used to explain the conductor.
“The key thing is what they see here is something underground that is very conductive, and because they see it under St. Helens and Mount Adams they’re assuming it's magma,” Caplan-Auerbach said. “There’s a lot of stuff it could be that’s less scary.”
According to the study, such a connection between the volcanoes would help explain the seismic activity during Mount St. Helens' massive eruption, seismic velocities in the northern area of the conductor inconsistent with sedimentary rock and the type of magma seen in the mountain’s most recent activity. The body would be more of a pulp than a fiery liquid, with 2 percent to 12 percent of it actually molten.
“We believe our results speak for themselves and are reluctant to extrapolate from the conclusions we reach in the paper,” Hill said in an e-mail.
However, the study has sparked debate within the scientific community, as many researchers say the area lacks signs commonly seen at similar chambers, such as the one under Yellowstone.
Seth Moran, a seismologist at the U.S. Geological Survey’s Cascades Volcano Observatory in Vancouver, Wash., said the area lacks the signs that accompany these chambers, such as geothermal vents, hot springs and frequent earthquakes, as well as more volcanoes between Mount St. Helens, Mount Adams and Mount Rainier. He also notes that near Rainier, where the conductor comes within a kilometer of the surface, one can see sedimentary rocks that agree with the current theory.
“There is negative evidence, which is a lack of things you’d expect to see, as well as positive evidence for the current theory,” Moran said. “If there was magma, you’d expect to see it.”
Burgess said it is well known that chains of volcanic mountains often have ‘roots’—deep bodies of unerupted magma—and many mountains have them. The study suggests a large root system exists under the Cascades, and Burgess said it is unrealistic to compare the Cascade magma chamber to others with different geology, such as Yellowstone.
“The Yellowstone analogy really does not apply at all,” Burgess said. “Yellowstone and the Cascades are completely different tectonic settings and thus result in completely different volcanoes.”
He also pointed out that the chamber has vents—Mount St. Helens, Mount Adams and possibly Mount Rainier.
Both Caplan-Auerbach and Moran commended the researchers for their work and feel it helps expand the knowledge of the workings of volcanoes in the region, as well as promotes further investigations of the area. However, both Moran and Caplan-Auerbach agree the jump to a magma chamber is a little extreme.
“The data they collected is pretty good and they definitely contribute to a greater understanding of the Mount St. Helens area with their work,” Moran said. “It really boils down to their interpretation.”
For the magma chamber being a super-volcano like that under Yellowstone, Caplan-Auerbach, Moran and Burgess agree there is not a fiery monster waiting to blow.
As Burgess said there is absolutely nothing to suggest that the chamber even has the ability to erupt. The study’s findings, no matter how recent, do not pose any dire implications for the residents of Washington.
“We are talking about processes that operate on geologic time scales,” he said. “Just because it has recently been discovered doesn’t make it ‘new.’”
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