Geologists ‘Closely Monitoring’ Rising Magma Under Oregon Volcanic Region

Interferogram image made from InSAR monitoring, showing 1995-2001 ground uplift in the Three Sisters. Courtesy USGS

Magma beneath land close to the South Sister volcano in Oregon has caused an uplift in the area, the United States Geological Survey (USGS) said, offering potential clues to future volcanic activity.

The uplift was detected by satellites used by the USGS to monitor the region. The data they collected showed an uplift of about 0.9 inches occurred between the summer of 2020 and August 2021 across a space 12 miles in diameter, roughly three miles away from South Sister.

Magma uplift can indicate volcanic activity below the surface of the Earth. A research paper published in Frontiers in Earth Science in January 2021, which examined the Three Sisters Volcanic Center in Oregon (where the South Sister volcano is), found that changes to the uplift behavior in the area could be considered an important indicator of future volcanic activity.

However Jon Major, the scientist-in-charge at the USGS Cascades Volcano Observatory, said that the activity did not have scientists overly concerned about a possible imminent eruption at the site.

"The current uplift at Three Sisters is small and progressing very slowly, so we do not expect an eruption soon. We infer that emplacement of magma at depths of about 4 miles below ground is responsible for this uplift. If that magma was to work its way closer to the surface and possibly head toward eruption, we would expect to see other signs indicting as much," he said.

"As magma got closer to the surface we would see more rapid uplift, possibly focused in a narrower area. The magma would break rock to make pathways to the surface and so we would see increased numbers and sizes of earthquakes as well as a shallowing of earthquake source areas. Magma would also release its stored gasses, and we would see an increase in gas output. These are among the typical signs we look for before an eruption; we see no such signs at present," Major said.

South Sister last erupted over 2,000 years ago, spewing ash and thick viscous lava flows down its flanks. These impacts are still visible today.

Major said that the most recent uplift at the site occurred during the mid-1990s and continued for more than 25 years, bringing a series of earthquakes with it that were so small most could not be felt by humans.

The scientist said that if the most recent uplift reported by the USGS followed the same pattern, it would likely slow down.

"Small bursts of episodic earthquakes may occur as the crust adjusts to magma input... if the magma started working its way to even shallower depths and approached the surface, we would expect to see increases in earthquakes, uplift, and gas release," he said.

Before the recent increase, the USGS stated the rate of uplift at the South Sister location had reportedly slowed down since scientists first recognized the phenomenon in the mid-1990s.

“From 1995 to 2020, the area rose approximately 12 inches (30 centimeters) at its center,” USGS stated in a recent release. “Although the current uplift rate is slower than the maximum rate of about 2 inches per year measured in 1999-2000, it is distinctly faster than the rate observed for several years before 2020.”

Despite the excitement, USGS and Burns have said that the public is not in any immediate danger. The volcano status is currently listed as “green,” and there is no sign of an imminent eruption.

“While any magmatic intrusion could eventually lead to a volcanic eruption, an eruption would likely be preceded by detectable and more vigorous earthquakes, ground movement (deformation), and geochemical changes,” stated USGS. “In general, as magma moves upward during an intrusion, it causes continued or accelerated uplift, fractures rock to generate swarms of earthquakes, and releases significant amounts of volcanic gases, such as carbon dioxide. We do not detect any of these signs currently.”

Burns told KOIN a team of scientists with Cascades Volcano Observatory will continue to closely monitor uplift at the site and will be ready if a threat is detected.

“We have great maps for the whole Three Sisters area,” Burns explained, “So if [the volcano] does come back to life, we will know which people are going to have to get out of the way and be prepared for it.”

He continued, “The good news is we’re prepared for it … We’re still at ‘green,’ but things are coming back to life now. Mother Nature writes her own history book, so it will be interesting to see what she will come up with this time.”

The above story is based on materials provided by USGS.

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