Science & Technology

The First Sounds of Volcanic Thunder Ever Recorded Are ... Disappointing

Volcano eruptions are among the most fearsome and awe-inspiring events nature can throw at you. They're rock-meltingly hot, ear-shatteringly loud, and fill their surroundings with a thick fog of ash that can last for weeks. They can even trigger lightning strikes, adding an electric fireworks show and an extra rumble of thunder to an already ostentatious performance. Scientists had never been able to hear that thunder over the din of the volcano's own rumblings — until now. In March 2018, a team of researchers led by Matthew Haney of the U.S. Geological Survey announced that they had finally recorded volcanic thunder. The recording is ... not that impressive. But believe us when we say the scientific achievement certainly is.

Rock 'n' Roll!

The eruption that the researchers recorded was that of the Bogoslof volcano in Alaska's Aleutian Islands, between 2016 and 2017. You might remember the event from the trouble it caused — the massive ash cloud led to an aviation warning in the area. Because Bogoslof is mostly underwater, it's proven tough for scientists to access. As a result, Haney and his team recorded the eruption from 60 kilometers (roughly 40 miles) away — and the fact that they still picked up plenty of noise is testament to the volcano's power. Their breakthrough was announced in the journal Geophysical Research Letters.

So how did they know this was really thunder and not just the rumbles of the volcano? First of all, they cross-checked their recordings with maps of volcanic lightning in the area to unravel the specific timing. These rumbles were distinct and came from a slightly different direction than the eruption. They happened six different times, each three minutes after the lightning peaked. That told the researchers that this was "almost certainly" thunder caused by that lightning.

In the first half of the video below, you can hear the equivalent of 20 minutes of audio played at 60 times its original speed. Right around the 10-second mark of that clip, the eruption stops and makes the thunder especially pronounced. The second half is five minutes of audio played at 10 times its original speed, all recorded after the (different) eruption is over. The rumbles are just the volcano; what you're really listening for are the pops and clicks. Those are volcanic thunder.

Okay, so it's no screaming caterpillar or gravitational wave detection. It honestly sounds more like static on the mic than the awesome power of volcanic thunder. But just the fact that the researchers could tease that sound out of the much louder rumble of Bogoslof erupting is reason to celebrate. It's never been done before, after all. And now that Haney and his team have done it, it opens the door to other possibilities.

Do You Hear What I Hear

To know what volcanic thunder can tell us, it's important to know how volcanic lightning happens — something scientists just figured out in 2016. As ash erupts from the mouth of the volcano and rises upward, the individual ash particles rub together until they build up enough static electricity to form — zap! — a lightning bolt. The intensity of that lightning can tell scientists how big the ash plume is and, as a result, how dangerous it could be. The ability to detect volcanic thunder could put one more tool in the scientist's toolbox in order to help them make those measurements.

This kind of detection doesn't have to be done in real time. There are plenty of recordings and plenty of lightning maps out there, and many scientists might now be tempted to find thunder in their own audio clips. Haney thinks so. "I expect that going forward, other researchers are going to be excited and motivated to look in their datasets to see if they can pick up the thunder signal," he said in the press release about the discovery.

Volcano Lightning: How Does It Happen?

Written by Ashley Hamer April 3, 2018

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