Exploding volcanoes make noise similar to jet engines

In a new research, scientists have suggested that the large-amplitude signals from volcanic eruptions are similar to the noise produced by typical jet engines.

The research was done by scientists from Scripps Institution of Oceanography at UC (University of California) San Diego.

The research team speeded up the recorded sounds from two volcanoes and uncovered a noise very similar to typical jet engines.

These new research findings provide scientists with a more useful probe of the inner workings of volcanic eruptions.

Infrasound is sound that is lower in frequency than 20 cycles per second, below the limit of human hearing.

The study, led by Robin Matoza, a graduate student at Scripps Oceanography, measured infrasonic sound from Mount St. Helens in Washington State and Tungurahua volcano in Ecuador, both of which are highly active volcanoes close to large population centers.

"We hypothesized that these very large natural volcanic jets were making very low frequency jet noise," said Matoza, who conducts research in the Scripps Laboratory for Atmospheric Acoustics.

Using 100-meter aperture arrays of microbarometers, similar to weather barometers but sensitive to smaller changes in atmospheric pressure and low-frequency infrasonic microphones, the research team tested the hypothesis, revealing the physics of how the large-amplitude signals from eruptions are produced.

Jet noise is generated by the turbulent flow of air out of a jet engine.

Matoza and colleagues recorded these very large-amplitude infrasonic signals during the times when ash-laden gas was being ejected from the volcano.

The study concluded that these large-scale volcanic jets are producing sound in a similar way to smaller-scale man-made jets.

According to Michael Hedlin, director of Scripps' Atmospheric Acoustics Lab and a co-author on the research paper, "We can draw on this area of research to speed up our own study of volcanoes for both basic research interests, to provide a deeper understanding of eruptions, and for practical purposes, to determine which eruptions are likely ash-free and therefore less of a threat and which are loaded with ash."

Researchers also hope this new information can improve hazard mitigation and inform pilots and the aviation industry.