For years, it had been considered impossible to record the sounds of volcanic thunder. But a team of researchers has changed that, after analyzing months of recordings from an Alaskan volcano that yielded a few instances of the phenomenon.
In an attempt to identify the isolated sounds of thunder during a volcanic eruption, the scientists set up microphones near Bogoslof volcano in Alaska's Aleutian Islands, well before any eruptions had actually taken place. According to Phys.org, the observations were made over a period of eight months, from December 2016 to August 2017, and during this period, Bogoslof erupted a total of 64 times. Analysis of the recordings revealed that there were "cracking sounds" when the volcano erupted on March 8 and June 10, meaning that on those days, it was possible to actually hear volcanic thunder, marking the first time this was ever documented on audio. These findings were detailed in a paper published earlier this week in the journal Geophysical Research Letters.
"It's something that people who've been at eruptions have certainly seen and heard before, but this is the first time we've definitively caught it and identified it in scientific data," read a statement from Alaska Volcano Observatory seismologist Matt Haney, lead author on the new study.If volcanic eruptions can produce thunder, they too can result in lightning on very rare occasions, as noted by a report from Newsweek. At the moment, it isn't sure why volcanic thunder and lightning can be heard and seen respectively, but there are some theories that might explain such phenomena. As ash particles jostle against each other while being spewed out of an erupting volcano, this could cause them to get electrically charged to the point that lightning is created. Additionally, scientists have speculated that the ash plumes from volcanos might simulate a conventional thunder cloud due to the heights they can reach during eruptions — 3,000 to 4,000 feet into the atmosphere, according to Newsweek.
Although the researchers did not physically see volcanic lightning during their observations, their volcanic thunder recordings could help scientists detect the lightning, and also allow them to determine how large an ash plume may be during an eruption. Boise State University geophysicist Jeff Johnson, who did not take part in the new study, was quoted by Phys.org as saying that it's "notoriously difficult" to precisely measure the size of ash plumes, but since Haney's team found that the intensity of both the thunder and lightning when Bogoslof erupted were very similar, the findings might serve as a valuable aid in accurately determining how much ash has erupted.
"If you're locating thunder over a long area, you could potentially say something about how extensive the plume is," said Johnson.
Although Bogoslof's eruptions did not affect too many people, the ash plumes caused by these events were intense enough to disrupt flight paths, leaving airlines no choice but to reroute their flights.
As elusive as volcanic lightning may seem, Newsweek described the phenomenon as being exactly the same as "normal" lightning, but with a volcano erupting at the same time. However, it remains as mysterious as ever, and with Haney and his colleagues hoping to isolate further instances of volcanic thunder from their recordings, they hope to come even closer to understanding why it's heard and why lightning is seen during eruptions.