An erupting volcano produces massive, rumbling sounds but scientists proved that volcanic thunder, a previously undocumented phenomenon, is real.
The thunderclaps that follow a volcanic lightning can detect an eruptive activity.
Geophysicists recorded sounds from the Bogoslof volcano. The volcano, which was erupting for eight months from December 2017 to August 2017, is located in located in the Aleutian Islands of Alaska, a chain of over 50 volcanic islands in the northern Pacific Ocean.
Volcanic Thunder And Sounds From An Erupting Volcano
The unambiguous observed volcanic thunder is challenging because erupting volcanoes produce high amplitude acoustic waves due to the ejection of volcanic products at the vent, which often masks the thunder signals.
To be able to observe volcanic thunder from Bogoslof, scientists from the U.S. Geological Survey used microphones array located 60 kilometers away to detect volcanic eruptions. The volcanic lightning from the eruptions was mapped as well.
From the recordings, the researchers were able to isolate and identify volcanic thunder that they described as cracking sounds that were never heard or observed before, separately from the loud sounds of an erupting volcano.
They identified cracking sounds recorded on March 8 and June 10, 2017, as the signature of a volcanic thunder.
Volcanic lightning networks are said to be associated with the volcanic thunders. In their observation, the scientists noted that high-frequency thunder signals correspond with the timing and strength of lighting detections.
"In both cases, the thunder is associated with lightning that continues after a significant eruptive activity has ended. Infrasonic and sonic observations of volcanic thunder offer a new avenue for studying electrification processes in volcanic plumes," says Matthew Haney, a seismologist at the Alaska Volcano Observatory in Anchorage and one of the study coauthors.
When the scientists observed the data they gathered from the recordings, they realized that they knew precisely when to look for volcanic thunder because the signatures accompanied volcanic lightning.
Volcanic lightning is produced by charged particles in the ash clouds. In the Aleutian Islands, thunderstorms are rare, so when a flash of lightning occurs, eruptions follow.
Researchers could use volcanic thunder as a proxy for volcanic lightning to determine the volume of ash plume to be emitted by the volcano.
According to the study, volcanic thunder, if observable, would contain additional information on volcanic plume electrification that would complement lightning data.
"I expect that going forward, other researchers are going to be excited and motivated to look in their data sets to see if they can pick up the thunder signal," Haney said.
"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 at Boise State University who is not connected to the study.
The new study is published in Geophysical Letters, the journal of the American Geophysical Union.