To the untrained ear, volcanic thunder sounds like the rumble of a plane engine or a distant river. But scientists are really excited about the low hum, clicks and pops that were recorded during a March 2017 eruption at Bogoslof volcano.
That’s because it’s the first time a team has recorded the sound of volcanic thunder. The recordings come from Bogoslof volcano in the Aleutian Islands. Scientists say the recordings are just the beginning of a treasure trove of clues scientists are exploring in the wake of Bogoslof’s nine month eruption. One thing they’re learning is that lightning and thunder may help predict the risk ash clouds pose to aircraft.
John Lyons, a geophysicist at the Alaska Volcano Observatory, says scientists weren’t sure if volcanic thunder was loud enough to hear over the roar of an eruption.
“It wasn’t that we didn’t think it was happening,” Lyons said. “It was that we didn’t know if we could record it.”
Sensors picked up the thunder from 40 miles away. Volcanic lightning and thunder occur when bits of ash and ice collide during an eruption.
Isolating the sound of thunder could help scientists better understand ash plumes — which pose a threat to airplanes.
Lyons says it’s a big deal because scientists are getting more out of their infrasound sensors than they imagined, even after an eruption has stopped.
“Maybe there are some signals you disregarded previously as noise, but those might actually be telling you something about processes happening in the eruption cloud as it moves away in the atmosphere from the volcano,” he said.
Lyons says the recordings show infrasound sensors can be used to detect volcanic lightning, especially smaller sparks that might not register on global lightning monitoring networks.
At Bogoslof, scientists had another tool specifically designed for lightning detection. Last spring, Volcanologist Alexa Van Eaton helped install new lightning sensors that can help signal when eruptions begin.
Although the Aleutians have a lot of rain, thunderstorms are rare — making lightning a prime tool for forecasting eruptions. In fact, Van Eaton says this is first time lightning was used as a near real-time monitoring tool.
“The World Wide Lightning Location Network (WWLN) was putting out rapid alerts that were triggering whenever there was lightning around the volcano and that was sending text messages to the AVO scientists and letting them know, ‘dude, lightning. There’s probably an eruption,’” said Van Eaton.
She says lightning is one clue that helps scientists understand volcanic eruptions. It can make a difference in determining how big eruptions are and alert researchers that eruptions may be happening.
From when Bogoslof started erupting in December 2016 to when it stopped in August 2017, Van Eaton says half of the 60 or so eruptive events produced globally detectable lightning.
While volcanic lightning has been noted for well over a hundred years, the number of scientists in the field is small. Van Eaton says it’s gone from people thinking volcanic lightning was just a cool phenomenon to realizing that understanding it can help keep people safe from ash.
And she says the data from Bogoslof is a windfall.
“It’s letting us ask cool questions like what happens if the eruption shoots seawater into the atmosphere along with the ash?” Van Eaton said. “Does that make more lightning or less lightning?”
They found that wetter eruptions had less lightning overall. Van Eaton says that was the opposite of what they expected. She says that’s important because it could help further refine predictions for when ash may pose a risk to health and safety.
“Being able to use the lightning to figure out if the eruption was wet or dry is potentially really important for thinking about how long the ash is going to be in the atmosphere and how quickly it might reach Dutch Harbor, or any of the airports, and how long aircraft are going to have to avoid the area,” she said.
Van Eaton says dryer eruptions — eruptions with lots of lightning — tend to have ash particles that stick around longer and have the potential to travel farther.
She believes volcanic lightning should be used with seismometers, infrasound sensors, and satellite data to help keep the people who live near volcanoes safe.