Volcanic eruption like Mount St. Helens: ‘It will happen again in Cascades’

May 2015 – EUGENE, Ore. – Mount St. Helens caught science a little by surprise. A volcano hadn’t erupted on the United State mainland outside Alaska and Hawaii since California’s Lassen Peak in early 20th Century. And modern science had yet to witness an eruption quite like St. Helens. “I think this was a turning point in the way people approached these kinds of potentially active, explosive volcanoes,” said Mike Dungan, a volcanologist with an office at the University of Oregon. St. Helens didn’t just erupt: it blew up. The force of the May 18, 1980, eruption wasn’t just vertical; it was lateral, sending a side of the mountain rocketing down slope as a wall of boiling mud and rock. The eruption killed 57 people – and put scientists and policy makers on notice.

“It’s only a matter of a short time – decades or something – before another one of these things occurs,” Dungan said. “A sector collapse eruption like Mount St. Helens – it will happen again in Cascades.” Research at the University of Oregon is shedding new light on the cause of the explosion. Geologists like PhD student Kristina Walowski are conducting research into how ocean water seeps into offshore plates as they plunge deep into the earth. “What’s really interesting is that water is really important because it lowers the melting temperature of a rock and when that happens you can create magma,” she said. “The water is really the key thing that causes the expansion, just like when champagne comes jetting out of a bottle,” said Paul Wallace, professor geological science at UO. “It’s a foamy material because of the gas present in gas bubbles.”

The May edition of Nature Geoscience published the findings by the Oregon team, funded by a National Science Foundation Grant. “Ultimately the water that makes them so explosive is coming out of the ocean,” Wallace said. “And eventually as the plate moves like a conveyor belt, it gets returned back down into the inside of the earth. It’s not like you’re pouring cups of water into the interior of the earth, right?” Walowski said. “There’s a complicated set of reactions and breakdowns where these rocks are changing shape, and releasing water little by little by little.” So which of the Cascade volcanoes is next in line to erupt? It’s difficult to predict, but geologists are watching. “We’re really in the midst of a technology explosion when it comes to monitoring volcanoes, using all kinds of things using remote sensing instruments on satellites,” Wallace said. “Mount St. Helens is still the most frequent in the Cascades,” Walowski said, “and based on that, it may be the most likely to go again.” –KVAL