An earthquake has struck just miles north of an Alaskan volcano currently showing signs of unrest and the potential for eruption.
The US Geological Survey reported a magnitude 4.6 quake near Petersville, approximately 86 miles from Mount Spurr. According to the Alaska Earthquake Center: “We have reviewed a M4.6 earthquake that occurred at 10:38 a.m. local time, 52.4 miles deep and 34 miles north of Skwentna.” The centre added, “This event was felt throughout Anchorage and the Matanuska-Susitna region.” Anchorage, which is more than 100 miles from the epicentre, also reported tremors.
Nearly 200 reports of shaking have been submitted to the USGS from this sparsely populated area, which has been on the verge of a volcanic eruption in recent months.
Mount Spurr remains under an ‘Advisory’ due to low-level unrest, with occasional small earthquakes being detected beneath the volcano. A 2021 study published in Nature revealed that most volcanoes—especially those already showing signs of unrest like Mount Spurr—can be triggered to erupt by nearby earthquakes. The risk increases when magma pressure and underground gas buildup are present.
The USGS said the earthquake was detected 52 miles below the surface, a depth at which energy tends to spread more widely. This means that while shaking may be felt over a large area, it is often less intense unless the quake’s magnitude is particularly high.
Residents across Anchorage shared their experiences online. Melissa Palmer posted on Facebook: “[I] felt it in Anchorage (Airport Heights).” Others noted movement in Sand Lake and north of Healy.
The Petersville region sits above the Broad Pass thrust fault—a southeast-vergent fault responsible for forming the Peters Hills basin. The Broad Pass thrust fault remains active and could potentially generate powerful earthquakes ranging from magnitude 7.6 to 7.8, posing a significant seismic hazard.
With nearly 300,000 people living in Anchorage, locals have been watching Mount Spurr closely since March, when scientists warned an eruption could be imminent.
The Alaska Volcano Observatory (AVO) issued its latest update on Tuesday, stating: “Low-level unrest continues at Mount Spurr with occasional, small earthquakes occurring beneath the volcano. Nothing was observed in partly cloudy to clear satellite images over the past day. Clear webcam views of Mount Spurr’s summit crater showed minor vapor emissions.” The AVO also noted: “Fluctuations in unrest are common at volcanoes and eruptive activity remains possible, but unlikely.” They explained that similar slowdowns in activity were seen before eruptions in 1992, with seismic activity fluctuating before eruptive events.
When Mount Spurr was previously under a ‘Watch’, elevated gas levels were detected from its summit and side vent—the same vent that last erupted in 1992.
During that time, Matt Haney, scientist-in-charge at the AVO, told DailyMail.com that any eruption would most likely occur at the Crater Peak side vent and would be explosive. Such an event could send multiple ash plumes up to 50,000 feet into the air.
Each explosive episode would last three to four hours, with ash clouds potentially blanketing Anchorage and neighbouring communities in dust. An eruption would also trigger destructive mudslides and avalanches of volcanic debris racing down Mount Spurr at speeds exceeding 200 miles per hour. “Fortunately, there are no communities in that radius that would be affected,” Haney said.