The volcanic island of Anak Krakatau erupting in Indonesia. Image: Byelikova Oksana/Shutterstock
Volcanologists have managed to capture audio of a phenomenon known as ‘volcanic thunder’ in a feat that was once believed to be impossible.
Those who have been able to observe volcanic eruptions from a safe distance may have more than likely heard rumbling sounds known as ‘volcanic thunder’.
Because of the intense heat and accumulation of smoke and ash, erupting volcanoes contain their own stormy microenvironments.
For example, lightning is quite common as the particles of ash and ice scrape and collide with each other to become electrified. However, for some reason, scientists have been unable to clearly identify the sound of the resulting thunder for analysis, despite being able to hear it with their own ears.
In fact, with everything going on in such a confined space, it was thought impossible to obtain clear data of the phenomenon.
But now, a research team from the Alaska Volcano Observatory analysing an eruption from the Bogoslof volcano in Alaska’s Aleutian Islands has returned what appears to be the first clear audio recordings of volcanic thunder.
A satellite image showing Bogoslof erupting on 28 May 2017. The eruption began about 18 minutes prior to this image, and the cloud rose to an altitude greater than 12km above sea level. Image: Dave Schneider/Alaska Volcano Observatory and US Geological Survey
Perfect conditions
The chain of 50 islands are monitored constantly by microphones and seismic activity recorders for impending eruptions. Last year, two eruptions – which occurred on 8 March and 10 June – created the ideal conditions for volcanic thunder to be recorded.
This is because both eruptions generated immense ash plumes that persisted for several hours after eruption, leaving time for the microphones to pick up the uninterrupted sound of volcanic thunder.
Now, for the benefit of us all and science, the team has released audio of what is surely one of the rarest recordings out there.
Really, really loud
“Understanding where lightning is occurring in the plume tells us about how much ash has been erupted, and that’s something that’s notoriously difficult to measure,” said Jeff Johnson, a geophysicist unconnected with the study.
“So, if you’re locating thunder over a long area, you could potentially say something about how extensive the plume is.”
The actual tracking of the recordings required some detective work as a series of global lightning sensors had picked up the initial flashes, which were then compared with the audio recordings of the microphones on a nearby island 60km away.
Matt Haney, lead author of the study, said the fact that it was picked up so far away means the thunder must have been very loud indeed.
“If people had been observing the eruption in person, they would have heard this thunder,” he said. “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.”
The team’s research has been published in the journal Geophysical Research Letters.
