Just after 3 a.m. Saturday, Donna Willoya, 62, was making tea at her home in Wasilla when she heard a loud bang, followed by series of more big bangs that lasted for at least 10 minutes.
Willoya, who had set an early alarm to check for northern lights activity, had no idea what she was hearing.
She was one of many Alaskans who heard the mysterious booming sounds early Saturday. Many posted on social media seeking answers. Hours later, it became clear that what they heard was caused by the eruption of an undersea volcano near Tonga nearly 6,000 miles away.
“Never in my life would I have thought it was a volcano from the South Pacific,” Willoya said.
Hearing a volcano, or any sound, so far away from its origin “is a pretty rare phenomenon,” said David Fee. He’s a research professor who works at the Geophysical Institute at the University of Alaska Fairbanks and as a scientist with the Alaska Volcano Observatory.
Through his work with the Alaska Volcano Observatory, Fee monitors a group of sensors that track sound waves in the atmosphere that can determine the direction the waves are coming from.
“When I looked at the data this morning, it was pointing back at that volcano. You know, it’s thousands of miles away, but it just kind of helps us pinpoint where it’s coming from,” he said.
Sound travels slowly through the atmosphere. In this case, it would have taken the audible sound waves about seven hours after the explosion to be heard in Alaska, according to Fee.
Scientists will often record really low-frequency sound waves around the world following big volcanic eruptions or explosions, “but it’s quite rare to be able to hear them audibly,” he said.
There were just a few other times Fee could think of when audible sound traveled so far and wide, including the Novarupta Katmai eruption of 1912, the largest eruption of the 20th century, and the 1883 Krakatoa eruption.
“So yeah, this is pretty unique,” he said.
Fee was also awake in the early hours of Saturday morning, with his baby and wife in Fairbanks.
“We were inside and we heard something, kind of like a low rumbling. It almost sounded like someone was walking outside or something,” he said.
He didn’t think anything of it at first — “sometimes in the winter in Alaska, you hear weird things” — but later, he realized what it likely was.
It’ll take further research to say for sure what was different about this eruption. Fee said the main thing scientists know at this point is that “it takes a lot of energy and a lot of sound to produce audible sound at long distances.”
The fact that Alaskans could hear any kind of sound was indicative of just how large this volcanic eruption really was, he said. The audible sounds from the eruption lasted for about 30 minutes while the low frequency sounds lasted longer, around 2 hours.
Low-frequency sounds typically travel greater distances than audible sounds because they lose energy at a lower rate. That’s why you can hear the bass from a concert or stereo much further away, Fee explained.
The fact that the explosion happened beneath the sea likely contributed to the explosiveness, but not how far the sounds traveled, Fee said.
He said he was interested in learning more about whether other places also heard the booms, which may have “propagated nonlinearly through the atmosphere.” He’s also curious about whether there was something unique about Alaska’s location at play.
Alaskans from Anchorage to Fairbanks and Cordova, along the Kenai Peninsula and elsewhere, reported deep, thunder-like blasts and booms early Saturday. The sounds were also heard in Canada.
They described what they heard and their initial impressions of what was causing the sound: military cannons, fireworks, routine blasting for avalanches, target practice, home intruders, slamming doors, violent winds, kids jumping up and down. One Alaskan said by email that what they heard was “how I imagined world war 3 would sound like.”
“It sounded like dogs were running up and down the stairs yet they were lying right next to the bed,” wrote a Reddit user.
In Wasilla, Willoya at first thought the sound could’ve been caused by her tea kettle. Then she considered a range of possibilities: a moose digging near her basement, artillery exercises at Joint Base Elmendorf-Richardson across the inlet. But usually, warnings are posted by the military weeks in advance before major drills — and she’d seen none.
“I kept looking over towards the (military) base,” she said. “But it was not really that noise. It was deeper.”
[Correction: This story was updated to clarify that audible sounds from the eruption lasted about 30 minutes while lower-frequency sounds lasted around two hours.]