Study of magma under Mount St. Helens underway

Researchers hope findings improve forecasting abilities

By Tom Vogt, Columbian science, military & history reporter

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Did you know?

• There typically are two volcanic eruptions in the Cascade Range each century, seismologist Seth Moran said. In the 20th century, they were at Mount Lassen (1915) and Mount St. Helens (1980).

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LAHAR VIEWPOINT — Kelley Hall lay flat on her stomach, peeking into a 4-foot-deep hole.

The University of Washington graduate student is part of a team that will give scientists a much deeper glimpse — miles and miles deeper — at what lies beneath Mount St. Helens.

They've started an ambitious project to chart something they will never actually see: the plumbing system that feeds magma to the volcano. Researchers hope what they learn about that pipeline will improve their ability to forecast volcanic eruptions.

The two-year effort hit the ground a few days ago when crews installed the first of 70 seismic sensors that will be placed around Mount St. Helens. One of the installations took place Friday near Lahar Viewpoint, named for the volcanic mudflow that swept down the southeast flank of the volcano.

"Imaging Magma Under St. Helens" features U.S. Geological Survey scientists based in Vancouver, including Seth Moran.

The Cascade Volcano Observatory seismologist said the goal is to sort out the relationship between underground magma and volcanoes. It's kind of a geologic version of the chicken-or-egg riddle, he said: "The big-picture question is, why are volcanoes where they are?'"

The IMUSH researchers are using three types of geophysical monitoring to create the subterranean images.

"Nobody has thrown this much technology and expertise at one volcano system," Moran said.

Some of the technology was on display Friday, when scientists invited members of the local media to watch the installation of a seismometer. The site east of Cougar is a link in the project's passive seismic network, set up to detect earthquakes.

The seismometer that went into the ground Friday is a hypersensitive instrument, said Peter Frenzen, a scientist with the Mount St. Helens Volcanic Monument.

Teachable moments

That's why the first assignment for Hall, the UW grad student, and Cornell University senior Tim Clements involved shovel work. They had to dig the hole where the seismometer would be housed, buried inside a vault that's actually a plastic garbage can. In addition to protecting the seismometer, the vault will minimize the effects of fluctuating temperatures.

Cornell University professor Geoff Abers was the other seismologist overseeing the installation. There were some teachable moments along the way. About 8 inches down, Hall and Clements hit a white crust. It was a layer of pumice, likely from an eruption in 1490 — just before Columbus set off on his first voyage.

Clements punched through the crust with a steel wrecking bar and the students kept shoveling. Once it was deep enough to accommodate the 44-gallon trash can, Hall stretched out on the grass, reached down deep into the hole and used a garden trowel to do the finish work at the bottom.

For stability, the seismometer was placed on a concrete footing. Abers and Moran mixed up a bag of concrete. As they poured the wet concrete into the form at the bottom of the hole, Moran offered another observation.

"That's what a lahar looks like."

Work on magnetotelluric monitoring, which measures fluctuations in the earth's electromagnetic field, has also started.

The third data stream will come from active-seismic monitoring, in which scientists will create their own versions of quakes by setting off explosive charges; that research will take place in July and August.

Mount St. Helens is a good place for this type of research. It has been the most active volcano in the Cascade Range during the last 2,000 years.

It has erupted twice in the last 35 years, the second time just a decade ago, ensuring the presence of magma in the system now.

And, thanks to those eruptive phases, scientists already have a lot of information about the upper-crust portion of the magma system as well as seismic data.

Mount St. Helens also more accessible than most volcanoes for people and equipment.

Eventually, scientists will recreate the IMUSH game plan at other volcanoes, Moran said.

"Through the course of three or four or five, we'll get a sense of how comparable magma systems are at depth," he said.

States differ

There already are plenty of questions to explore, like the difference between Oregon and Washington magma systems.

"There are more volcanoes in Oregon," Moran said. While Washington can boast the iconic Mount Rainier, there are more (although less impressive) volcanic features like cinder cones in Oregon.

Maybe it's easier for magma to work its way up through the underlying rock to the surface in Oregon, he said. "The fractures are not as clamped down."

Moran also wonders, "Is there less magma produced up north?"

The research will mean plenty of grunt work for Hall and Clements, but the college students say it's worth it.

"I'm having a great time," Clements said. "Most of the year, I'm behind a computer. This is the fun part."

"I was aware of what's involved," Hall said. "I did field work in Nevada, and it was 110 (degrees.)"