A surge in earthquakes beneath a volcano near Alaska’s largest city is drawing increased attention from geologists.
Mount Spurr, located approximately 80 miles (129 kilometers) northwest of Anchorage, last erupted in 1992, releasing an ash plume nearly 12 miles (19 kilometers) high. The eruption disrupted air travel and prompted residents to wear masks. The Alaska Volcano Observatory warns that another eruption from the 11,100-foot (3,383-meter) stratovolcano could significantly impact the city.
In October, the observatory elevated Mount Spurr’s alert level from green to yellow after noticing a marked rise in seismic activity and ground deformation detected through satellite imagery. According to observatory scientist David Fee, around 1,500 minor earthquakes have been recorded beneath the volcano this year, compared to an annual average of about 100.
While this uptick is notable, Fee emphasized that it is "not an enormous amount" and does not necessarily indicate an imminent eruption. Similar activity occurred between 2004 and 2006 but eventually subsided without an eruption.
“We haven’t observed any major changes in our data suggesting an eruption is near,” Fee said. “This has been a period of low-level unrest, but we’re closely monitoring for any developments.”
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Scientists are using seismic instruments, satellite data, and webcam feeds to detect signs of an impending eruption, such as increased earthquakes, surface deformation, the formation of a summit lake, or fumaroles—gas and vapor-emitting vents.
Mount Spurr’s last eruption in 1992 originated from the Crater Peak vent, located about 2 miles (3 kilometers) south of the summit. That event deposited roughly a quarter-inch of ash in Anchorage, forcing residents indoors or to wear masks. The ash cloud drifted as far as Greenland. A similar eruption occurred in 1953, while the summit’s last known eruption dates back over 5,000 years.
Volcanic ash, composed of sharp, angular particles, can halt jet engines, which led to airport closures in Anchorage and nearby areas during the 1992 eruption. Such disruptions are especially impactful in Alaska, where limited road access makes air travel crucial. Today, the Anchorage airport is a global cargo hub, ranking among the busiest alongside Memphis, Hong Kong, and Shanghai due to Alaska’s strategic location near Asia.
Mount Spurr is part of the Volcanic Ring of Fire and one of 53 Alaskan volcanoes that have been active within the past 250 years.