Scientists Follow Rising Magma Beneath Mount Rainier

By Jenna Iacurci

Using a network of extremely sensitive instruments, scientists are painting a more detailed picture of the inner workings of the molten rock deep beneath some of North America’s most active and dangerous volcanoes.

The network, acting like a giant metal detector, has helped geophysicists understand the process that brings magma from 50 miles below the surface to active volcanoes like Mount Rainier in Washington State.

Such findings could help improve early warnings of possible eruptions, they say.

Mount Rainier and Mount St. Helens are some of the most dangerous volcanoes among the scores of them located in Washington’s Cascade Range, stretching down the West Coast from British Colombia in Canada to Northern California. Mount St. Helens had a deadly eruption in May 1980, killing about 50 people and spreading its ash across 11 states.

As part of a study published in the journal Nature, scientists presented a detailed picture of the deep underground plumbing below Mount Rainier and followed its rising magma.

They found that the majority of the volcano’s magma forms deep within the Earth’s mantle, where it then rises up in a roughly vertical column towards the surface, collecting in a reservoir underneath the volcano’s 14,000-foot peak.

They study helped researchers settle the question of whether the melted magma “goes up through a network of cracks, or whether it gets dragged up in little bits, or rises in diapirs,” lead author R. Shane McGary from the Woods Hole Oceanographic Institute told the Los Angeles Times.

Diapirs, he explained, are “just like what you would see in a lava lamp: a blob that gets heated up and rises.”

According to the study, Mount Rainier sits atop a massive “chimney” of magma, a configuration unlike other neighboring volcanoes in Oregon. It suggests that even close volcanoes can have different eruption dynamics.

“I would regard Mount Rainier as a much more serious short-term threat than Mount Jefferson in Oregon, which lacks a flow path,” McGary said, however, he does not believe that an eruption is likely in the near future.

The sensor network beneath Mount Rainier can detect changes in the movement of magma by monitoring fluctuations in magnetic conductivity caused by shifts in underground geological structures, researchers said.

Given the technique’s efficacy, the next step, according the McGary, is to do similar studies at other volcanoes along the West Coast.

“I would be really interested in seeing what Mount St. Helens looks like using this technique,” he added.