Researchers at the Alaska Volcano Observatory in Anchorage have managed to record the sound of volcanic thunder for the first time, Smithsonian magazine and The Guardian report. It's extremely difficult to differentiate the sound of thunder from the sounds of the eruption itself, which has made conclusively identifying the sonic phenomenon on tape impossible until now.
"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," Alaska Volcano Observatory seismologist Matt Haney explained in a press release. He and his colleagues published their observations in the journal Geophysical Research Letters.
Using a microphone array almost 40 miles away, Haney's team picked up the sounds of volcanic thunder in March and June 2017 in the midst of two explosive eruptions of the Bogoslof volcano, a mostly submarine volcano in Alaska's Aleutian Islands. (Only about 300 feet of the approximately 6000-foot-tall volcano is above sea level.) The eruptions resulted in huge plumes of ash, a prime environment for volcanic lightning to occur. The volcano continued to generate ash plumes long after the eruptions ended, so the researchers could compare the post-eruption lightning with the timing and volume of the sounds they picked up on the microphones, and positively identified the volcanic thunder. They found that the intensity of the lightning was about the same as the intensity of the thunder's noise.
The technique could allow scientists to study volcanic lightning more easily by using the sound of thunder as an approximation, which may indicate how big the ash plume could grow. That information could reveal dangers for nearby aircraft.
You can hear the thunder for yourself in the audio tracks below. The recordings are sped up, and the thunder sounds clicks and pops. The whirring sounds in the first recording are the eruptions themselves.