A 2025 volcanic eruption at Mount Spurr near Anchorage is “likely” according to a new bulletin by the Alaska Volcano Observatory.
The timing of the eruption and its size remain uncertain, the observatory said in a notice published Tuesday, and it’s also possible that there may be no eruption at all.
Spurr, whose summit is 75 miles west of Anchorage, is the closest active volcano to Alaska’s largest city.
The new bulletin follows one published last month that indicated 50-50 odds of an eruption. Since then, said coordinating scientist David Fee, two flights above the volcano have found high levels of sulfur dioxide, carbon dioxide and other gases that indicate the presence of magma near the surface.
Sulfur dioxide levels during one flight last week were nine times higher than a similar flight in December, and data from the first March flight was preliminarily confirmed by another flight on Tuesday, prompting the new bulletin.
“There was basically nothing coming out before, and now there’s a lot of gas, particularly CO2 coming out, which usually, when we’ve seen this at volcanoes in Alaska and across the world, it means that eruption is getting more likely,” Fee said.
Since April 2024, observers have been tracking a growing number of earthquakes under and near the volcano. They’ve also watched the ground near the volcano bulge upward.
It’s similar to what the mountain did before its 1992 eruption, which closed area airports and caused Southcentral residents to stay inside to avoid ash.
If the mountain does erupt, the observatory advises that up to a quarter-inch of ash could fall on Southcentral Alaska. Under a microscope, volcanic ash often resembles small flakes of glass. Inhaling it can cause breathing problems. Air filters can become clogged, and flights may be postponed or canceled to avoid ash clouds.
An eruption will likely be preceded by weeks of escalating activity, including nonstop earthquakes and melted ice and snow atop the volcano. That’s kept scientists from raising their alert levels.
“If we were to see strong, sustained volcanic tremors, that would be kind of a telltale sign that we think an eruption is much closer. We have not seen that yet, and we’re looking very closely for any signs of it. There could be other signs as well,” Fee said.
Some observers have noted a steam plume from Spurr’s summit. That’s not a sign of imminent eruption, Fee said. Plumes can be created by atmospheric conditions just as much as volcanic ones.
In addition, an eruption is likely to come from Crater Peak, the source of Spurr’s 1954 and 1992 eruptions, rather than the summit of the volcano itself.
“The recent gas data suggest that a new pathway towards the Crater Peak vent has opened, and that fresh magma may rise and erupt there. Crater Peak is the site of all historical eruptions. The last known eruption from Spurr summit occurred several thousand years ago,” the new Alaska Volcano Obervatory bulletin states.
As the AVO monitors Spurr, the organization itself is suffering budgetary tremors caused by the Trump administration’s erratic firings and budget freezes.
The AVO is a cooperative effort between the state and federal government. In February, federal staff had their payment cards frozen, interrupting the telecom links that transmit data from the volcano.
“Most of those (issues) have been worked around at this time,” said Fee, a state employee.
“We haven’t had layoffs. What we have had are kind of some of the other impacts,” he said. “There’s also some concerns with the lease of the (AVO) building in Anchorage, but hopefully that will be resolved as well.”
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