It’s been six years since Mount St. Helens returned to relative slumber after its last eruptive phase, but the notorious volcano is quietly recharging for the next one, scientists said Wednesday.
There are no signs of an impending eruption, according to the U.S. Geological Survey. But ongoing analysis has confirmed that magma underneath the volcano is re-pressurizing — and has been for years. The buildup is likely caused by a surge of new magma several miles below the surface, according to the USGS.
That doesn’t mean Mount St. Helens is going to erupt again any time soon. It does, however, underscore the need to keep constant watch on it and other volcanoes in the region, said Seth Moran, a seismologist with the USGS’s Cascades Volcano Observatory in Vancouver.
“The message to us as an observatory is, we need to be ready,” Moran said.
Mount St. Helens has been the Northwest’s most closely monitored volcano since its catastrophic 1980 eruption. Additional eruptions continued through 1986, and another dome-building eruption occurred from 2004 to 2008.
Scientists have two lines of evidence showing pressure building up again since then, Moran said. Small earthquakes under the mountain are consistent with that pattern, he said. And GPS units have shown slight land inflation and deformation even miles away from the crater, he added.
In many cases, the push is outward. GPS devices located north of the volcano have shifted northward; units positioned south of the volcano have shifted farther south. The difference is negligible, but noticeable — centimeters over several years, Moran said.
Scientists have seen that before. While Mount St. Helens was acting up between 2004 and 2008, a GPS unit near Johnston Ridge Observatory moved toward the volcano, Moran said. In the years since, the same unit has begun shifting outward again, suggesting re-pressurization, he said.
A vast monitoring network continues to watch Mount St. Helens for signs of increased unrest. And researchers are well-equipped to detect signs of any future eruption should the volcano decide to wake up again, said Steve Malone, a retired seismologist with the Pacific Northwest Seismic Network at the University of Washington.
The activity measured in recent years appears more subtle than what was observed during the volcano’s last quiet phase from the late 1980s to the early 2000s, Malone said. But conditions can change, and they can change quickly, as the last eruption showed, he said.
“It’s not going to erupt in the next couple weeks,” Malone said. “But after that, we don’t know. It could be months. It could be years. It could be decades.”
Wednesday’s announcement doesn’t reflect any new hazard at Mount St. Helens, said Carolyn Driedger, outreach coordinator at the Cascades Volcano Observatory. “In fact, the rate of inflation has declined since 2008,” she said.
Action pointing to an impending eruption might include more frequent and more intense seismic activity, more pronounced land deformation or changing gas patterns, Driedger said — again, nothing Mount St. Helens is currently showing.
Not surprisingly, this week’s news still generated considerable attention. Scientists recognize that any hint of activity at Mount St. Helens turns heads, Moran said.
“There’s always a line to walk with these things,” Moran said. “You don’t want to come out and say something like that until you’re sure. At the same time, if there’s something going on with the volcano, you want people to know about it.”