New research lays groundwork for promising new technique for audio-only eruption tracking
28 July 2021
AGU press contact:
- Liza Lester, +1 (202) 777-7494, [email protected] (UTC-4 hours)
Contact information for the researchers:
- Jacopo Taddeucci, Isituto Nazionale di Geofisica e Vulcanologia, Rome, Italy, [email protected], (UTC+2 hours)
- Juan José Peña Fernández, Ludwig-Maximilians-Universität München, Munich, Germany, [email protected], (UTC+2 hours)
WASHINGTON—Hidden in the chaos of the first moments of a volcanic eruption is an ephemeral ring of smoke and ash that can give scientists important clues about how dangerous an eruption might be. A new study captures these volcanic vortex rings and their sound on high-speed video, potentially pointing to a new way to measure a volcano using only sound.
Volcanic vortex rings are curls of an eruption’s plume that form during the first seconds of an eruption, like the twisting ripples in water as you pull an oar through it. The size, speed, and composition of those curls reflect useful factors in assessing how hazardous the eruption is, like how intense the eruption is or how deep in the vent the eruption started.
But the rings are short-lived and can be difficult to measure in small eruptions. Larger eruptions can form visible vortices, but scientists cannot always get close enough to make the necessary observations. If it is dark or the mountain is wreathed in smoke, the rings may not be visible.
In the new study, a team of volcanologists and jet-stream physicists paired high-speed video with audio focused on the first seconds of eruptions at Stromboli volcano in Italy to listen to the vortex rings. The study is unique in its audiovisual approach and is the first to isolate the sound of a volcanic vortex ring.
Their work was published in the AGU journal Geophysical Research Letters, which publishes high-impact, short-format reports with immediate implications spanning all Earth and space sciences.
“There is a characteristic sound which is made by the vortex itself, which is a low, constant sound. The beauty of the of the vortex rings is that they are stable, and that means that they make a constant sound that is propagating over time,” said Jacopo Taddeucci, a volcanologist at Italy’s Isituto Nazionale di Geofisica e Vulcanologia and lead author of the new study.
With new knowledge about how a volcano’s tune is linked to its eruption, volcanologists can continue homing in on different volcanic processes and sounds to improve monitoring when visual or other techniques aren’t available.
“Even if we don’t see the eruption because it is cloudy or we don’t have a permanent camera over there, we will be able to know what is going on just by the sound,” Taddeucci said. “My hope is that by studying the sound of the eruption, we will be able to track changes in those parameters just by the noise. This is one of the future promises of this work.”
To pinpoint the sound of those elusive volcanic vortices, Taddeucci and his collaborators set up high-speed cameras and professional microphones several hundred meters from the vents of Stromboli. They also recorded video from a drone flying over the volcano as it let off steady spurts of eruptive jets, allowing the team to measure parameters like vent size. The jets are supersonic columns of hot gases, ash and smoke, reaching 100 to 300 meters (330 to 1000 feet) high at Stromboli.
Although the team could not see the rings they were trying to capture, when they filtered the video, dark smudges—the vortices—appeared. They measured the rings’ size and speed, and by precisely lining up the video with the audio, they isolated the low, steady rumble emanating from the vortices from the roar of the eruptive jet.
Because the vortices’ sounds were so distinctive and steady, the team was then able to correlate the frequency with other aspects of the rings. They found a clear link between vortex motion, its sound and vent size, the latter of which they measured with the drone. Other changes in a volcano’s ‘tune,’ including its eruptive jet, could be related to the vent’s internal structure.
“Vortex rings are quite sensitive to the parameters with which they are generated,” explained Juan José Pena Fernández, a fluid mechanics researcher and co-author of the new study. “If we record the acoustic generated by a vortex ring, we can know quite precisely the conditions that made it. So if there is a change in the volcano’s behavior, we could be able to detect it.”
Combining audio with high-speed visuals “makes perfect sense,” said Amanda Clarke, a University of Arizona volcanologist who was not involved in the study.
“I thought it was very creative and clever. It’s not easy to make these kinds of measurements in the field simultaneously,” Clark said. “For these kinds of [explosive] eruptions, the vortex structures can really tell you about the source conditions. But it’s not easy to tease that information out of the measurements that are not easily observable.”
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Notes for Journalists:
This research study will be freely available for 30 days. Download a PDF copy of the paper here. Neither the paper nor this press release is under embargo. Download videos associated with this release.
“Volcanic Vortex Rings: Axial Dynamics, Acoustic Features, and their Link to Vent Diameter and Supersonic Jet Flow”
- Jacopo Taddeucci (corresponding author), Isituto Nazionale di Geofisica e Vulcanologia, Rome, Italy
- Juan José Peña Fernández, Ludwig-Maximilians-Universität München, Munich, Germany
- Valeria Cigala, Ludwig-Maximilians-Universität München, Munich, Germany
- Ulrich Kueppers, Ludwig-Maximilians-Universität München, Munich, Germany
- Piergiorgio Scarlato, Isituto Nazionale di Geofisica e Vulcanologia, Rome, Italy
- Elisabetta Del Bello, Isituto Nazionale di Geofisica e Vulcanologia, Rome, Italy
- Tullio Ricci, Isituto Nazionale di Geofisica e Vulcanologia, Rome, Italy
- Jörn Sesterhann, Universität Bayreuth, Bayreuth, Germany
- Stefano Panunzi, Isituto Nazionale di Geofisica e Vulcanologia, Rome, Italy