Scientists eye Cascade range volcanoes

By Dylan J. Darling The Bulletin

After creating a buzz with recent studies about the magma below Mount Hood, a pair of researchers now want to study more volcanoes around the world — including South Sister.

Professor Adam Kent of Oregon State University and Associate Professor Kari Cooper of University of California-Davis, have determined that Mount Hood has been primed to erupt about 1 percent of the time during the past 100,000 years. The most recent eruptions of the tallest peak in Oregon were about 220 years ago and 1,500 years ago.

Examining rocks scattered on the mountain by those eruptions, Kent and Cooper found clues of how magma — molten rock — functions deep under Mount Hood. They found that much of the time the magma in a chamber under the volcano is relatively cool, making it sticky and stiff and the likelihood of an eruption low. They said this could be the case for other volcanoes.

“Most of them aren’t just sitting there, primed for eruption,” Cooper said.

Enter an influx of hot magma from deep within the earth and the situation can change quickly, she said. In just weeks or months the pool of nearly solid magma can “defrost,” she said, becoming a runnier liquid as it heats up. When its temperature rises so does the pressure in the magma chamber and the molten rock starts to move upward, increasing the possibility of an eruption.

Now that Kent and Cooper know how Mount Hood behaves, they want to compare other volcanoes.

“There are probably many other volcanoes that fall into this range of behavior,” Kent said.

The volcanoes they’d like to study include South Sister, just west of Bend, and Mount Pinatubo in the Philippines.

South Sister, an example of a relatively small volcano, last erupted about 2,000 years ago and Pinatubo, an example of a relatively large volcano, last had a major eruption in 1991. Cooper said South Sister isn’t more likely to erupt than Middle or North Sister, but she happens to already have studied rocks from lava flows on South Sister.

“Our plan is to kind of capitalize on that and expand the data set,” she said.

The researchers applied for a grant from the National Science Foundation and hope to receive about $500,000 for the next round of research, Kent said.

What Kent and Cooper have discovered so far underscores the importance of having monitors on and around volcanoes that could impact cities or towns, said Seth Moran, a seismologist at the U.S. Geological Survey’s Cascades Volcano Observatory in Vancouver, Wash. The observatory has installed monitors at Cascade volcanoes over the past decade, including at South Sister and Newberry Volcano, a broad volcano south of Bend that includes Newberry Crater.

With how quickly a volcano can go from slumbering to rumbling, showing signs of a coming eruption, Moran said there typically isn’t time to go out and install monitoring stations on a mountain as it becomes active. Weather, particularly deep snow, can also keep that from happening in the Northwest.

“We have to be out there before,” he said. “We have to be out there when it is quiet.”

When magma starts to move underneath a volcano, the mountain will put off seismic signals — small earthquakes. That’s what the monitors, which cost between $15,000 to $30,000 each, detect.

Moran said USGS scientists want to install monitors on and around Mount Hood, and add more around South Sister.

There are already five monitors around South Sister, the result of the bulge detected near the mountain about a decade ago. The bulge, an uplifting of ground, started in 1997 and was first noticed in 2000 by a federal scientist who noticed differences in radar images taken by satellite. Ground monitoring confirmed the 80-square-mile bulge in 2001.

There were concerns that the bulge may have been the early signs of a coming eruption or lava flow, but its growth has slowed or stopped in recent years. If there is growth, it is so slight it is undetectable. More monitors would help scientists know what is happening below the volcano and improve their chances of catching early signs of a coming eruption.

“There could be an eruption there tomorrow, there could be an eruption in 1,000 years,” Moran said. “We don’t know when, we just need to be ready for it.”

— Reporter: 541-617-7812, ddarling@bendbulletin.com

Editor’s note: This story has been corrected. In the original version, Kari Cooper’s title was misidentified. The Bulletin regrets the error.