Scientists now say it's likely Mount Spurr, the closest active volcano to Alaska’s largest city, will erupt within weeks or months.
So how do they know that? And what should residents of Anchorage and other nearby communities do in the meantime?
Here’s what to know.
(And if we missed your question, let us know in the form below.)
Why do scientists think Mount Spurr will erupt?
It’s showing all the signs: There have been recent earthquakes nearby, the volcano’s surface has expanded, there’s melting snow on its peak and there’s higher-than-normal emissions of volcanic gases.
“It's almost like we have a checklist of the usual signs that volcanoes give us before they progress to an eruption,” said Matt Haney, the scientist in charge at the Alaska Volcano Observatory. “And now we're seeing all four of those are giving us those indicators.”
Where exactly is Mount Spurr and what's close to it?
Mount Spurr is the tallest volcano in the Aleutian Arc, a batch of several dozen volcanic islands stretching from Southcentral Alaska along the Aleutian Chain to the Kamchatka Peninsula in the Russian Far East.
Spurr is about 80 miles west of Anchorage, but it’s in a very remote area. You have to charter a plane to get there and Haney said there’s little infrastructure there beyond the Alaska Volcano Observatory’s monitoring stations. The closest community is the village of Tyonek, on the west side of Cook Inlet, and it’s roughly 40 miles away by plane.
So, at this point, how certain are scientists that an eruption will happen anytime soon?
In February, scientists said there were equal chances the volcano would erupt or not.
Then, on March 12, they said it’s more likely to erupt than not. But there’s no specific percent chance to apply to it. So, for example, scientists can’t say there’s a 75% likelihood of eruption.
“We haven't quantified what that is in terms of a percentage,” Haney said. “But it is judged to be higher likelihood than this unrest dissipating.”
Will we get notice before it erupts?
Kind of.
It's unlikely scientists will be able to say, “Hey Alaskans, Mount Spurr will erupt in two hours!”
Instead, we'll see changes in the volcano’s alert level. As of March 19, Mount Spurr’s color code was yellow, or in “advisory” status, which means there’s increased unrest.
There are two levels above that:
- The “watch” or orange level means an eruption is even more imminent, or it could be underway but still posing only limited hazards to people. (That’s the case currently at Great Sitkin, far out in the Aleutian Islands, which is erupting and on “watch” status).
- The “warning” or red level means a hazardous eruption is “imminent, underway, or suspected.”
Scientists are watching Spurr for an increase in the four eruption indicators mentioned earlier that would trigger elevating its alert level.
“If we were to see volcanic tremor, if we were to see increased earthquake activity, increased gas emissions, increased melting of the snow and ice at the volcano, then those would be indications that we would go to the next level in our color code system, which is orange watch,” Haney said. “And then finally, if it were to go to an eruption, we would go to red warning.”
So, Mount Spurr could erupt in weeks or months. Is there any more specific timeline?
No, not right now.
Even if the volcano hits an orange alert, Haney said, that doesn’t necessarily mean an eruption is imminent. In fact, he said Mount Redoubt returned to yellow status after an orange alert in late January 2009.
“It stayed at orange for several weeks, and then in early March 2009 it was reduced to yellow because the tremor declines,” Haney said. “Then it went back to orange because there was a small steam-driven eruption, not a magmatic eruption, at the summit of Redoubt. Then again, the activity declined. It went to yellow.”
It finally ended up erupting between 10:30 and 11 p.m. on March 29, 2009. Redoubt’s eruption lasted several months and, at times, shot ash up to 65,000 feet.
So if Mount Spurr erupts, where will we hear about it?
In the event of a change in advisory – from yellow to orange or from orange to red – the Alaska Volcano Observatory will send out an alert on its website and notify its various community partners, like city and state emergency officials. You can sign up for alerts from the observatory here.
If you’re closer to it, can you actually hear it erupting?
That depends on a number of factors, including how close you are to the volcano, the size of the eruption and which way the wind is blowing, Haney said. However, most eruption sounds are at a frequency too low for human ears to pick up, he said.
“A Spurr eruption similar to those in 1953 and 1992 would likely not be audible for people in Anchorage but would be audible if one were close to the volcano. However it wouldn't be advisable to be that close,” Haney said. “Ash-producing eruptions can produce volcanic lightning in the ash cloud due to friction between volcanic ash particles, and that lightning produces thunder, which may be audible at further distances.”
What would an eruption look like and how long would it last? Do we know?
“More often than not, we have explosive eruptions that fragment magma and shoot ash, you know, 50,000 feet into the atmosphere,” Haney said.
The ash clouds produced by the eruption could move to Anchorage, if the wind happens to be blowing out of the west. In 1992, Spurr’s eruption resulted in three explosions, occuring in June, August and September. The 1953 eruption saw one explosion.
The eruptions can last from a few minutes to several hours, Haney said.
“For example, the eruptions in 1992, the ones in June, August and September each lasted approximately four hours,” Haney said.
What happened the last time Spurr erupted in 1992?
Spurr exploded three times. The winds during the first and third eruptions blew the ashfall to the north and south of Spurr, respectively.
“But on August 18, 1992, which was the second of the three explosions, the winds were blowing to Anchorage that day, and the ash was carried over Anchorage, and ashfall ensued on Anchorage,” Haney said.
In total, the city got hit with about an eighth of an inch of ash. In response, Ted Stevens Anchorage International Airport was shut down for about 20 hours.
We have more about impacts to air travel below, but first…
Who and what in Southcentral Alaska would be impacted if Spurr erupts?
Ashfall will be the main concern for Southcentral, said Jeremy Zidek, a spokesman for the state Division of Homeland Security and Emergency Management. When and where that might fall, though, depends on the circumstances.
“The impacts of a Mount Spurr eruption are unknown,” Zidek said. “There's a lot of key factors that will really come down to when it erupts, how long it erupts, what the wind direction is and other factors that could change, where that ash falls and how thick the ash falls.”
Zidek urged Alaskans to keep monitoring information from the volcano observatory. The division has also posted a list of frequently asked questions about a potential eruption on its website.
While there are communities closer to Spurr than Anchorage, like Tyonek and Beluga on the west side of Cook Inlet, Haney said they’re still far enough from the volcano that they shouldn’t be impacted by things like mudslides or pyroclastic flows.
Emergency officials from the Municipality of Anchorage, the Matanuska-Susitna Borough and the Kenai Peninsula Borough have held coordinated meetings since October in preparation for a potential eruption.
What are emergency agencies doing now?
Zidek said the division has been speaking with stakeholders across the region, including the volcano observatory, the National Weather Service, local emergency managers and utility companies.
“We've been kind of coordinating, coming together, developing information for people in the pre-eruption phase, so they have a good expectation of what a Mount Spurr eruption will look like,” he said.
Is there anything I should do now to prepare?
For now, Zidek said, the state is mainly asking that people remain informed.
“Understand that we may see an eighth of an inch to a quarter-inch of ash, or somewhere in that realm, in some places of Southcentral,” he said. “It all depends on the eruption and the wind speed, so there's a lot of things that where that ash is going to fall, that it's contingent on.”
You may want to have masks on hand now, Zidek said.
If the volcano erupts, what should I do to protect myself and my family?
Ashfall can cause respiratory problems.
The most important step to protect yourself from ashfall is wearing a mask when going outdoors, Zidek said.
“N95 masks are kind of the preferred mask that people would want to use, but really, any type of face covering that prevents ash from entering your lungs is better than no covering at all,” he said. “So if it's a surgical mask or an old COVID cloth mask, if it's some type of makeshift mask, that's better than nothing at all.”
Zidek also recommended avoiding tracking ashfall back inside. Pets should have only limited excursions outdoors during ashfall, and any ash that falls on them should be cleaned from their coats.
Beyond aviation concerns, Zidek said, ashfall is primarily an air quality issue, similar to spring allergens or dust from the sanding of roads.
Some longtime Alaskans have already experienced ashfall events during previous eruptions of Spurr and Mount Redoubt, he said.
“While the ash is a hazard, it's not something that we haven't dealt with before, from volcanoes and from other air quality events,” Zideksaid. “We just need to be aware of it and take some basic steps to protect ourselves.”
How does volcanic ash affect people with respiratory issues? Will they have to stay indoors?
Anchorage Chief Medical Officer Dr. George Conway said people should reduce the time they spend outdoors in the event of an eruption, especially if they have respiratory issues.
Minerals from the volcano known as silicates get suspended in air by an eruption, and they’re sharp and can cause inflammation of the lungs, Conway said.
“People that already have respiratory illnesses might be exacerbated, but they're both quite harmful if they're inhaled repeatedly or deeply, and they can contribute to both acute illness and chronic diseases,” Conway said.
Conway said there’s also a potential dual harm if Spurr’s eruption coincides with wildfires, as smoke from the latter could make air quality even worse.
Like with other natural disasters, Conway suggested people keep a cache of food, water and any necessary medication at their homes and shelter in place as much as possible. If they do have to leave their home, Conway, like Zidek, recommended people wear an N95 mask, as well as some kind of protective eyewear.
What about my property?
Cars are at particular risk from volcanic ash, which is abrasive and can damage windshields if it’s brushed away, Zidek said. Instead, try to pour washer fluid over the ash from the windshield, instead of using wipers.
Ash is also bad for car engines, and people should try to minimize driving during or after ashfall. If possible, cars should be stored in a garage or covered when not in use.
“We recommend that if people do need to drive in ashy areas that they change their air filters or clean their air filters regularly and change their oil more often,” he said.
Why is volcanic ash bad for air travel, anyway?
Ash is known to shut down jet engines and cause severe damage to plane exteriors. In December 1989, a 747 flew through ash from another nearby volcano, Mount Redoubt, and the plane’s engines shut down, forcing an emergency landing in Anchorage with 231 passengers aboard.
How might this affect Alaska commuter air traffic?
Both cargo and passenger flights would be impacted by an eruption, Ted Stevens Anchorage International Airport spokesperson Lex Yelverton said.
“(The) severity would depend on magnitude of the event and wind,” Yelverton said. “All airlines have their own internal operating practices, so for more details I would encourage them to ask airlines directly.”
Isn’t the Anchorage airport one of the busiest in the world? How is it preparing?
Officials with the Anchorage airport said they are working in collaboration with the Fairbanks International Airport to prepare for an eruption. That includes ensuring the airport has extra filters on hand, figuring out plans for ash removal and “reaching out to our partners both on- and off-airport to determine transportation and lodging accommodations, if needed, for any potentially stranded passengers,” Yelverton said.
On the ground in Anchorage, how would the city clean up ash?
Though the timeline is still uncertain, Anchorage Disaster Recovery Coordinator Kari Wiederkehr said if ashfall hits the city, it would likely coincide with street sweeping season.
“And when you do clean it up, if I remember correctly, it’s better if it’s wet so it doesn’t kick up a lot of dust,” she said.
A lot of the city’s response will be based on how much ash is blown into Anchorage, if at all, Wiederkehr said.
Is it safe to watch the eruption?
There should be ways for residents to see the eruption from a safe distance on a clear day at Anchoage’s Point Woronzof, Haney said.
“When it comes into Anchorage, it will be almost like a sandstorm with dark ash,” he said. “It will, if it occurs in daylight, it'll block out the sun.”
If it comes at night, Haney said, onlookers can be in for a different visual spectacle
“It can produce a large amount of lightning,” he said. “We call it volcanic lightning. It's due to charges getting set up by the ash particles scraping up next to each other.”
So what are scientists doing in the meantime?
They’re keeping a close eye on the volcano.
“We have a local seismic network of 11 stations that bring data back in real time, and we are watching it like a hawk,” Haney said. “We have automated alarms on the data, and we're looking for particular signs that will be the next step in the progression towards an eruption, should it go that way.”
If the volcano reaches that “watch” level, there will be a minimum of two scientists monitoring Spurr around-the-clock.
What else do you want to know about Mount Spurr and the likely eruption that we missed?
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