Trombone-like volcanic sound enables us to predict eruptions, scientists say

The University of Canterbury, Italian National Institute of Geophysics and Volcanology, and Boise State University researchers developed a modeling tool that uses sound waves from volcanic activity.

As the researchers suggested, the volcanic activities sound like a "trombone".

“Explosions at the top of the magma column excite sound waves, which are reflected at the top of the crater – just like inside a trombone, but on a much larger scale. As magma rises in the crater, the distance between the top of the magma column and the top of the crater decreases. This causes the pitch of the sound to increase – just like when a trombone is retracted," said Dr. Leighton Watson, a postdoctoral researcher.

The findings were published in Scientific Reports on October 19.

"By listening to the changing pitch, we can track the movement of magma within the crater. This has the potential to provide several hours of warning prior to an eruption, which could make a significant difference to those living near or visiting active volcanoes."

Melodies at Mount Etna

Dr. Watson and his colleagues researched these volcanic melodies at the active volcano Mount Etna in Sicily, Italy, where eruptions frequently occur, and lava is ejected over 1 km above the top.

The research also advances Dr. Watson's earlier investigations at Cotopaxi in Ecuador and Villarrica in Chile. The model will be modified in the following step of the research to make it applicable to a New Zealand environment.

"This model is for a volcano where there is a direct connection between the magma plumbing system—the lava lake—and the atmosphere. In New Zealand, two of the most hazardous volcanoes are Mount Ruapehu and Whakaari, which have crater lakes containing water between the magma and the air above," said Dr. Watson.

"Geological and Nuclear Sciences (GNS) already uses infrasound sensors to listen to volcanic activity, so I am interested to see if we can adapt the model to make it applicable to these systems. I'm also currently working on snow avalanches as a proxy system for pyroclastic flows and lahars."

Study abstract:

Infrasound is increasingly applied as a tool to investigate magma dynamics at active volcanoes, especially at open-vent volcanoes, such as Mt. Etna (Italy), which are prodigious sources of infrasound. Harmonic infrasound signals have been used to constrain crater dimensions and track the movement of magma within the shallow plumbing system. This study interprets the remarkable systematic change in monotonic infrasound signals preceding a lava fountaining episode at Mt. Etna on 20 February 2021. We model the changing tones (0.7 to 3 Hz fundamental frequency) as a rise in the magma column from 172 ± 25 m below the crater rim to 78 ± 8 m over the course of 24 h. The infrasonic gliding disappears approximately 4 h before the onset of lava fountaining as the magma column approaches the flare of the crater and acoustic resonance is no longer supported. The featured 20 February event was just one of 52 lava fountain episodes that occurred at Mt. Etna over the course of 9 months in 2021 and was the only lava fountain episode where dramatic gliding was observed as a subsequent partial collapse of the crater prevented future resonance. The results presented here demonstrate that analysis of infrasonic gliding can be used to track the position of the magma free surface and hence may provide information on the processes taking place within the plumbing system before eruptive activity.