Mount St. Helens Is ‘Recharging’ With Magma, Say Geologists

For most of the 20th century, Mount St. Helens kept silent vigil over the Pacific Northwest. Looming 9,600 feet above sea level, the young stratovolcano remained deceptively quiet throughout the early 1900s, with only a few grumbles occurring in 1903 and 1932. Then, in 1980, a plinian eruption of ash, lava, and debris would devastate Washington and kill 57 people.

Now, the US Geological Survey's Volcano Hazards Program has detected a number of earthquakes beneath the dormant volcano that indicate its once volatile magma chambers are slowly recharging. Mount St. Helens, the volcanologists said, "is still very much alive."

In the early spring of 1980, researchers with the USGS noticed that magma had begun to pour into Mount St. Helens, flooding its cryptodome and causing it to bulge in a way that hinted a violent explosion was imminent. The volcano's northernmost flank had grown outward by 450 feet, and was expanding at a rate of 6.5 feet per day. On May 18, seismographs at the University of Washington recorded a 5+ magnitude earthquake underneath the mountain. The geologic convulsion triggered an avalanche of debris from Mount St. Helens' summit, which popped the hydrothermal cork, so to speak, and released what would be the deadliest volcanic eruption in US history.

There's no reason to believe that the recent tremors are any immediate cause for concern. According to an update on the USGS' Facebook page, "There is absolutely no sign that it will erupt anytime soon." The absence of gas emissions and ground inflation, they note, is a pretty reliable assurance that things will remain calm in the near future.

However, the USGS has warned that Mount St. Helens will very likely erupt again in our lifetimes.

The precise timing and magnitude of the next eruption are impossible to predict, but after the catastrophic events of 1980, scientists have been constantly monitoring seismic activity around the volcano. What they do know is the intensity of subsequent explosions are unlikely to reach 1980-levels, as 1,300 feet of the mountain's summit were removed by the eruption, and the deep crater that was left behind won't produce the same type of powerful, lateral blast.

Beginning March 1, 2016, small magnitude earthquakes at depths between 1.2 to 4 miles occurred beneath Mount St. Helens. The smallest hit seismographic magnitudes of 0.5 or less, while the largest reached a magnitude of 1.3. To put that in perspective, quakes with magnitudes of 2.5 or less aren't usually felt by humans. Over the past eight weeks, the agency reported, more than 130 quakes have been formally located by the Pacific Northwest Seismic Network, and are steadily increasing.

The swarms are believed to have been caused by a subterranean chamber that's gradually filling with magma. As molten rock begins to pool underground, immense stress is put on the layers of rock that surround it. Fluid is forced between cracks in the strata, resulting in the tectonic shift of small faults, or earthquakes.

"It can take many years for a volcano to recharge between eruptive periods. We knows this from factual observation at St. Helens. It last erupted in 2004-2008, prior to that 1989-2001 and 1980-1986. Notice there are pauses between eruptive periods…we are in a pause with signals that recharge is occurring," the USGS added in a comment on their post.

For those still concerned about a potential explosion, it's important to recognize that this is all very normal behavior for a volcano like Mount St. Helens. Small eruptions and dome growth continued from 1980 to 1986, and again in 1989 through 2001. Between 2004 and 2008, the volcano experienced another reawakening and set off a series of steam and ash explosions.

Mount St. Helens is indeed gearing up for another eventual blast, but the explosive outcome of today's magma pooling won't be seen for another many years. Hopefully this next time around, everyone will be prepared enough to admire it from a distance.