▶️ Experts eyeing new, harmless volcanic activity on South Sister


If you’ve been around Central Oregon for a while, you’ll probably recall the magma bulge found near South Sister in the 1990s.

Now, the United States Geological Survey discovered another 12-mile bulge in the same area after reviewing data from June 2020 until August 2021.

“Data from satellite radar images show an uplift of about 0.9 inches or 2.2 cm (about the width of an adult’s thumb) occurred between the summer of 2020 and August 2021 across an area 12-mile (20-km) in diameter,” according to the Cascades Volcano Observatory.

The volcano is still in the green zone, meaning an eruption is very unlikely, but the event is still leaving scientists fascinated.

“And why is it so exciting?” I asked Hal Wershow, an Assistant Professor of Geology at Central Oregon Community College.

“Oh man,” said Wershow, after bursting into laughter.

He said he didn’t know where to start.

“The Earth is inflating upwards,” Wershow said, “It’s a very small amount, we’re talking an order of inches. There’s no way a human being would be able to detect it.”

The lift suggests that magma around 4 miles deep is shifting, causing the ground to rise and fall over the years.

“This is really telling us, sort of a rearrangement of the plumbing of the volcano,” said Josef Dufek the Director of the Center for Volcanology at the University of Oregon.

Dufek was recently awarded a grant to conduct research with the University of Oregon at the Three Sisters, monitoring activity just like this.

That similar situation in the 1990s surfaced again in the early 2000s. 

In 2004 and 2006, USGS scientists described a similar phenomenon and reassured the region that though a bulge could indicate a future eruption, it was extremely unlikely.

“So probably,” Wershow said, “this will stop tomorrow, a year from now, a decade from now, and there will have been no eruption.”

“It’s not likely to erupt,” Dufek said.

The only local eruptions occurring within the last 15,000 years were minor explosions at or near South Sister, making her the most active of the three stratovolcanoes.

“What we had at Mount St. Helens in 1980, that is not the most frequent type of volcanic eruption,” Wershow said.

However, even though the new phenomenon is not a potential “big boom”, the activity near the roughly 120,000-year-old mountain is giving scientists more data for a better understanding of Central Oregon’s ever-changing landscape.

Along with the moving magma, scientists also located several mini earthquakes in the same area, another calling card for bulges like this one.

All that continues the fascination towards the famous sisters.

“A lot of geologic processes are quite slow and steady,” Dufek said “but not so necessarily with volcanoes and I think that’s one of the fascinations with volcanoes.”

“Every single human being in Central Oregon has looked up at those volcanoes and gone, ‘WOW!’” Wershow said.

Here is a link to a geological survey scientific investigation map, used for work on the Three Sisters.

Here is the link to the 25-year magmatic inflation journal kept about the activity at the Three Sisters.

Here is a quick fact page about the Three Sisters and their volcanic activity.



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