<figure class="wp-block-image size-full"><figcaption class="wp-element-caption">The summit of Mount Spurr on Oct. 24, 2024. (Wyatt Mayo/Alaska Volcano Observatory)</figcaption></figure>

Scientists continue to monitor Mount Spurr, a volcano to the west of Anchorage and a huge chunk of the state’s population, after signs of unrest this spring, and again in the fall.

The Alaska Volcano Observatory raised its color code for Spurr to yellow, or “advisory” status, Oct. 16.

The observatory’s Scientist in Charge, Matt Haney, says that was after seismometers picked up an increased number of small earthquakes at the volcano and GPS sensors showed it was swelling up.

Haney says that’s all likely due to magma moving beneath Spurr’s surface.

Listen:

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This interview has been lightly edited for length and clarity.

Matt Haney: The surface of the Earth swells or moves outward, it moves upward and outward, from the the intrusion of of magma beneath the volcano. And then that intrusion also kicks off little earthquakes at the volcano. When I say little, these are earthquakes that if we were at Mount Spurr, we wouldn’t feel.

Casey Grove: So right now, with Spurr, it could progress toward an eruption. It’s totally possible that there would not be an eruption, and we’re at least a couple steps away from that. But if it is on the track towards an eruption, why do people need to know about that, and why do we watch it so closely?

MH: Spurr is the closest volcano to Anchorage. So it’s the closest to the infrastructure, the population centers, of Southcentral Alaska. And we don’t need to look further than the 1992 eruption at Spurr, which didn’t occur from the summit of the volcano. That’s another interesting part of Spurr. It happened from a vent that’s not the summit, it’s two miles south, that we call Crater Peak. So in 1992 it erupted from Crater Peak, and it deposited ash on Anchorage about a eighth of an inch, which is significant, and that darkened the skies in the middle of the day. And, you know, significantly it shut down the airport for 20 hours. So that’s a really important impact. You know, anything like that we want to have a lot of lead time to prepare for something like this. There needs to be, you know, measures taken to mitigate those types of impacts to our society.

CG: Well, and then, I mean, there was a real specific impact. Didn’t a plane fly through some ash and have some problems there?

MH: Very close in time, but the volcano to the south of Spurr, Redoubt, erupted three years before Spurr did in 1992. So Redoubt, in 1989 and then also into 1990, erupted, generated similar ash clouds to 50,000, 60,000 feet into the atmosphere. And there was a KLM jet coming from Europe, and it encountered the ash cloud. And at that time, not nearly as much was known about this effect, the effect of ash in jet engines and the warning systems were not in place at that time. And it flew into the ash cloud from Redoubt in December 1989 and caused them to stall and a passenger jet began to fall out of the sky. And then, fortunately, the pilots were able to restart the engines before it crashed. But certainly, there’s all that we have, all the improvements that we’ve made since then are intended to avoid situations like what happened at Redobut in 1989.

CG: And I guess part of that is like whatever direction the wind is blowing, when or if it erupts?

MH: Right, and that played out in 1992, as well. Spurr erupted three times in 1992, but it only put ash onto Anchorage one time. So it erupted in June 1992. The winds were such that the ash went to the north. It also erupted in September 1992, and on that day in September, the ash tracked more towards the Mat-Su Valley. But in August of 1992, it was that day that the winds were bringing it directly over Anchorage. So yeah, there’s the uncertainty whether this unrest at Spurr that we’re observing now will even lead to an eruption, or it could go to eruption, but then on that day, it could be that the winds could not be directed over Anchorage. So several factors at play that would lead to a situation like in August 1992.