Mount Spurr’s summit crater is seen from the air on March 7, 2023. Escaping gas from one of the volcano’s main fumarole and a dry crater floor can be seen. (Photo by Taryn Lopez/Alaska Volcano Observatory)
Mount Spurr, whose volcanic ash darkened Anchorage’s skies in 1953 and 1992, may be building toward another eruption, according to a statement issued Thursday by the Alaska Volcano Observatory.
For months, observatory scientists have monitored a growing number of earthquakes beneath and near the volcano, snow melting atop it, and bulging ground around it.
Observatory scientists now believe that activity has grown to the point that there’s an equal chance between no eruption and an eruption from Spurr’s Crater Peak in the near future.
“Indeed, that’s where we are, based on the anomalous data streams that have come in,” said Matt Haney, scientist in charge of the Alaska Volcano Observatory in Anchorage.
Haney said the assessment came after more than two weeks of discussion among observatory staff.
There’s also a small chance of an explosion at Spurr’s summit, a point about 75 miles west of Anchorage that hasn’t erupted in the past 5,000 years.
“We’re watching it very closely,” Haney said. “We’re saying that there’s unrest above background (levels), but it’s uncertain if this is actually building to an eruption.”
Spurr’s activity since April 2024 is similar to what the mountain did before Crater Peak’s 1992 eruption, which closed area airports and caused Southcentral residents to stay inside to avoid ash.
The recent activity is also similar to what was seen at the mountain between 2004 and 2006, when there was no eruption.
On the observatory’s four-step warning scale, Spurr is still at the second-lowest step, “advisory.” That would change if scientists begin seeing conditions like what occurred at Spurr in 1992.
That year, an eruption was preceded by three weeks of escalating activity at the volcano, including nonstop seismic tremors and huge amounts of melting ice and snow atop the mountain.
“We haven’t seen those signals yet, but we’re watching it very closely, since Spurr is, in Alaska, one of the very highest-threat volcanoes. It’s the closest volcano to Anchorage. So it’s keeping us busy at AVO,” Haney said.
More than 200 earthquakes have been detected at Spurr in the past week, but that’s short of the nonstop shaking that occurred before the 1992 eruption.
“These are very small (earthquakes). If we were out there at Spurr, we wouldn’t even feel them,” Haney said. “These are Magnitude 1 earthquakes. They have no discernible shaking, but they’re important because they’re telling us about the conditions inside the volcano. Every day, we’re locating dozens of these small earthquakes, and just in the past month, we’ve begun to see more earthquakes.”
On Friday, AVO scientists took advantage of a blue-sky day in Southcentral Alaska to fly over Spurr and take gas samples, looking for elevated levels of sulfur dioxide and carbon dioxide that could be a sign of an approaching eruption.
Data from that flight was not immediately available, and two prior overflights didn’t find unusual levels of those gases.
Haney said a maintenance flight was also scheduled Friday to remove snow from instruments around the mountain.
The volcano observatory is a collaborative effort between the USGS, University of Alaska and state geologists. Normally, its attention is spread across the state, from the Aleutians to Southeast Alaska’s Mount Edgecumbe. Spurr’s activity is forcing scientists to focus, Haney said.
“It’s a time where the whole observatory is coming together and discussing, trying to make sense of the real-time data that we’re obtaining,” he said.
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