Mount Spurr, a volcano near Alaska's biggest city, Anchorage, has been showing signs of activity for the past 10 months. This isn't the first time the volcano has caused concern. Located in the Aleutian Arc, about 75 miles west of Anchorage, Mount Spurr has been the subject of close monitoring by experts.

The Alaska Volcano Observatory has detected hundreds of small earthquakes beneath the volcano. This, combined with ground deformations, suggests that magma and fluids are moving underground. These changes can cause the ground to swell or deform. The rising magma and other fluids can also heat up surrounding areas on their way to the surface.

Scientists have noticed changes at Mount Spurr's summit, too. A small lake has formed within the crater, and there's some warmer water and gas coming out as well. These observations have scientists on alert, but they can't predict exactly when or if the volcano will erupt. The best they can do is keep a close eye on the situation.

The risk of an eruption is currently estimated to be 50-50. If it does erupt, the main hazards would be ash clouds that could disrupt air travel and potential ash fall over regional communities, including Anchorage. The uninhabited area around Mount Spurr would be at risk of pyroclastic flows, mudflows, and ballistic showers. However, there are no communities or cities in the volcano's immediate vicinity, so the local threat is low.

Mount Spurr has a history of eruptions. It last erupted in 1953 and three times in 1992. These eruptions were relatively small but explosive, dispersing volcanic ash over areas of interior, south-central, and southeastern Alaska. In 1953, the columns of ash the explosions produced rose up to 65, 000 feet above sea level and deposited about 6 mm of ash in Anchorage. One of the 1992 eruptions closed down the Ted Stevens Anchorage International Airport for 20 hours, and numerous air-quality alerts were issued for several days after the eruption.

The volcano alert level for Mount Spurr is currently at advisory, one step above normal. Experts are keeping a close eye on the data, looking for any changes that might suggest an eruption is more likely in the near future. The east flank of Mount Spurr is shown on February 7, 2025. Matt Loewen/Alaska Volcano Observatory/US Geological Survey

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