When volcanoes erupt, they often do so thunderously. But until recently, scientists have been unable to distinguish the sounds of an eruption from the sounds of volcanic thunder.
In addition to the loud roar of eruptions, lightning strikes that spring from volcanic plumes create loud claps of thunder.
Now, in new audio clips published in the Geophysical Research Letters, scientists are revealing the first recordings of the phenomenon.
The crackling sound was identified using microphones set up to detect eruptions coming from Bogoslof volcano in Alaska’s southwestern Aleutian Islands. Over an eight-month period, the microphones picked up a mixture of eruption booms and lightning cracks. Only by cross checking a map of volcanic lightning were they able to distinguish what on the recording was volcanic thunder.
It wasn’t until a study published in 2016 that scientists even knew what caused volcanic lightning.
Similar to lightning that forms in clouds, volcanic lightning occurs when electricity flows between positively and negatively charged particles. Unlike atmospheric lightning, however, lightning born from volcanoes forms much closer to the ground, in the plumes of an eruption. And also unlike atmospheric lightning, volcanic lightning doesn’t always move downward.
The result is a series of jagged bolts of electricity that appear to jump out of a volcano’s mouth. Visually, it’s one of the most stunning shows put on by nature.
By better understanding how and when volcanic thunder cracks, scientists say they’ll be able to better predict the size of a plume coming off an eruption.
In recordings published in the study, the sounds of thunder can be initially difficult to distinguish from the sounds of the eruption. The volcanic blasts sound like low, deep rumblings, while the thunder sounds more like brief clicks and pops.
On the Aleutian Islands, the thunder-detecting microphones will be a useful tool for scientists who are constantly monitoring the region to detect eruptions. During the period monitored for the study, eruptions sometimes produced plumes that towered more than 20,000 feet high.
“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,” said lead author and seismologist Matt Haney in a press release.