Not all volcanic eruptions are created equally. Thin and runny magma results in lazy flows, like the kind you’ll find in Hawaii; meanwhile, thick and sticky magma results in catastrophic explosions Mount Vesuvius-style. These big boy booms spurt out clouds of hot rock and ash, which have the ability to create cracks of charged lightning bolts, once they reach the atmosphere. This creates volcanic thunder, though we might not ever know it: It’s usually couched in a messy affair of loud bangs and rumbles that can reverberate for miles.

That’s why it’s all the more spectacular that scientists have captured the first recording of volcanic thunder: Teasing out sounds of thunderclaps from the overall chaos of eruption noises is a task most scientists thought was impossible. However, on Tuesday, geophysicists announced in Geophysical Research Letters that they were able to capture thundering cracks while recording the Bogoslof volcano. This volcano, which is part of a 50-volcano chain of islands near Alaska, erupted more than 60 times between December 2016 and August 2017.

Volcano
A satellite image of the Bogoslof volcano on March 11, 2017.

While those eruptions happened, the research team set up shop on an island 40 miles away, using seismic sensors to detect when an eruption would occur. When signs pointed to an explosion, they wiped out an array of microphones and recorded from the first eruption until the last ash plumes dissipated several hours later. The scientists then compared the timing and location or lighting strokes to the recordings in order to identify the sounds of thunder.

On June 10 and March 8, the researchers managed to record distinct bursts of thunder sounds. The timing and volume of the sounds, the researchers explain in a statement released Thursday, “matched the lighting data in a way only thunder could.”

The quick clips and pops sound like this, only sped up 60 times:

This audio file is 20 minutes of data recorded in March, sped up 60 times. 

People have previously claimed that they’ve heard volcanic thunderclaps, but now we have a way to actually document the phenomenon. Analyzing volcanic thunder offers scientists a new way of detecting volcanic lighting as well as a potential new way to estimate the size of an ash plume: Because thunder matches the intensity of lighting, and lighting intensity indicates to scientists how big and hazardous volcanic plumes may be, then the thunder sounds themselves could also serve as a warning.

“Understanding where lighting is occurring in the plume tells us how much ash has been erupted, and that’s something that’s notoriously difficult to measure,” geophysicist Jeff Johnson, Ph.D., who was not part of the study, explained in a statement released on Tuesday from the American Geophysical Union. “So if you’re locating thunder over a long area, you could potentially say something about how extensive the plume is.”

That would have been helpful when Bogoslof actually erupted: Last year, the onslaught of eruptions interrupted major flight paths as planes were forced to find new routes because of the massive plumes of ash.


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