Hunga volcano eruption provides an explosion of data
The massive Jan. 15, 2022, eruption of the Hunga submarine volcano in the South Pacific Ocean created a variety of atmospheric wave types, including booms heard 6,200 miles away in Alaska. It also created an atmospheric pulse that caused an unusual tsunami-like disturbance that arrived at Pacific shores sooner than the actual tsunami.
Those are among the many observations reported by a team of 76 scientists from 17 nations that researched the eruption’s atmospheric waves, the largest known from a volcano since the 1883 Krakatau eruption. The team’s work, compiled in an unusually short amount of time due to significant scientific interest in the eruption, was published today in the journal Science.
David Fee, director of the Wilson Alaska Technical Center at the University of Alaska Fairbanks Geophysical Institute, is a leading author of the research paper and among four of the center's researchers involved in the work.
The Hunga eruption, near the island of Tonga, has provided unprecedented insight into the behavior of some atmospheric waves. A dense network of barometers, infrasound sensors and seismometers in Alaska — operated by the Geophysical Institute’s Wilson Alaska Technical Center, Alaska Volcano Observatory and Alaska Earthquake Center — contributed to the data.
“Our hope is that we will be better able to monitor volcanic eruptions and tsunamis by understanding the atmospheric waves from this eruption,” said Fee, who is also the coordinating scientist at the Geophysical Institute’s portion of the Alaska Volcano Observatory.
“The atmospheric waves were recorded globally across a wide frequency band, and by studying this remarkable dataset we will better understand acoustic and atmospheric wave generation, propagation and recording,” he said. “This has implications for monitoring nuclear explosions, volcanoes, earthquakes and a variety of other phenomena.”
The researchers found particularly interesting the behavior of the eruption’s Lamb wave, a type named for its 1917 discoverer, English mathematician Horace Lamb.
The largest atmospheric explosions, such as from volcanic eruptions and nuclear tests, create Lamb waves. They can last from minutes to several hours.
A Lamb wave is a type of guided wave, those that travel parallel along a material’s surface and also extend upward. With the Hunga eruption, the wave traveled along Earth’s surface and circled the planet in one direction four times and in the opposite direction three times — the same as observed in the 1883 Krakatau eruption.
“Lamb waves are rare. We have very few high-quality observations of them,” Fee said. “By understanding the Lamb wave, we can better understand the source and eruption. It is linked to the tsunami and volcanic plume generation and is also likely related to the higher-frequency infrasound and acoustic waves from the eruption.”
The Lamb wave consisted of at least two pulses near Hunga, with the first having a seven- to 10-minute pressure increase followed by a second and larger compression and subsequent long pressure decrease.
The wave also reached into Earth’s ionosphere, rising at 700 mph to an altitude of about 280 miles, according to data from ground-based stations.
A major difference with the Hunga explosion’s Lamb wave compared to the 1883 wave is the amount of data gathered due to more than a century of advancement in technology and a proliferation of sensors around the globe, according to the paper.
Scientists noted other findings about atmospheric waves associated with the eruption, including “remarkable” long-range infrasound — sounds too low in frequency to be heard by humans. Infrasound arrived after the Lamb wave and was followed by audible sounds in some regions.
Audible sounds, the paper notes, traveled about 6,200 miles to Alaska, where they were heard around the state as repeated booms about nine hours after the eruption.
“I heard the sounds but at the time definitely did not think it was from a volcanic eruption in the South Pacific,” Fee said.
The Alaska reports are the farthest documented accounts of audible sound from its source. That is due in part, the paper notes, to global population increases and advances in societal connectivity.
“We will be studying these signals for years to learn how the atmospheric waves were generated and how they propagated so well across Earth,” Fee said.
Other Geophysical Institute scientists involved in the research include graduate student Liam Toney, acoustic wave analysis, figure and animation production; postdoctoral researcher Alex Witsil, acoustic wave analysis and equivalent explosive yield analysis; and seismo-acoustic researcher Kenneth A. Macpherson, sensor response and data quality. All are with the Wilson Alaska Technical Center.
The Alaska Volcano Observatory, National Science Foundation and U.S. Defense Threat Reduction Agency funded the UAF portion of the research.
Robin S. Matoza of the University of California, Santa Barbara, is the paper’s lead author.
ADDITIONAL CONTACT: David Fee, 907-474-7564, dfee1@alaska.edu.
NOTE TO EDITORS: Photographs are available at the Geophysical Institute website. The research paper is available here.
JOURNAL
Science
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Atmospheric waves and global seismoacoustic observations of the January 2022 Hunga eruption, Tonga
ARTICLE PUBLICATION DATE
12-May-2022
*Free* A close-up of the 2022 volcanic eruption that sent waves around the world
Observations from two studies of the January 2022 volcanic eruption of Hunga volcano, Tonga, show a complex main event that was as energetic as the 1883 Krakatau eruption, one of the deadliest and most destructive volcanic events in recorded history. The observations also uncover that the tsunami generated by this eruption was partially driven by an unexpected atmospheric wave. This set of observations will be helpful for disentangling the event and understanding the propagation of waves through the atmosphere and ocean. On 15 January, 2022, a massive volcanic eruption occurred on a small, uninhabited island in the South Pacific, Hunga Tonga-Hunga Ha‘apai. The Hunga Tonga eruption was one of the most powerful recorded, with audible sound detected over 10,000 kilometers from the source. In one study, Robin Matoza et al. present infrasound and seismic recordings, along with other geophysical observations, that characterize this event. An atmospheric Lamb wave, characteristic of energetic atmospheric events, circled the planet four times and was similar to the 1883 Krakatau eruption. The eruption also generated long range infrasounds and ionospheric interations, along with global tsunamis. In a second study focused on the tsunamis, first waves from which arrived more than 2 hours earlier than expected for conventional tsunamis, Tatsuya Kubota and colleagues investigated the generation and propagation mechanisms of the tsunami “forerunner.” Typically, tsunamis generated by volcanic eruptions are created by water displacement from deformation and atmospheric pressure waves that travel at about the same velocity as the tsunami. Kubota et al. found that for the Hunga Tonga eruption, a different sort of atmospheric pressure wave – a Lamb wave – also contributed to tsunami propagations. This interaction resulted in tsunami waves arriving much earlier than expected. Future tsunami models should incorporate this phenomenon, the authors say.
JOURNAL
Science
ARTICLE TITLE
Atmospheric waves and global seismoacoustic observations of the January 2022 Hunga eruption, Tonga
ARTICLE PUBLICATION DATE
12-May-2022
Eruption’s echoes
Massive eruption of Tongan volcano provides an explosion of data on atmospheric waves
Peer-Reviewed PublicationThe Hunga volcano ushered in 2022 with a bang, devastating the island nation of Tonga and sending aid agencies, and Earth scientists, into a flurry of activity. It had been nearly 140 years since an eruption of this scale shook the Earth.
UC Santa Barbara’s Robin Matoza led a team of 76 scientists, from 17 nations, to characterize the eruption’s atmospheric waves, the strongest recorded from a volcano since the 1883 Krakatau eruption. The team’s work, compiled in an unusually short amount of time, details the size of the waves originating from the eruption, which the authors found were on par with those from Krakatau. The data also provides exceptional resolution of the evolving wavefield compared to what was available from the historic event.
The paper, published in the journal Science, is the first comprehensive account of the eruption’s atmospheric waves.
Early evidence suggests that an eruption Jan. 14 sunk the volcano’s main vent below sea level, priming the massive explosion the following day. The Jan. 15 eruption generated a variety of different atmospheric waves, including booms heard 6,200 miles away in Alaska. It also created a pulse that caused the unusual occurrence of a tsunami-like disturbance an hour before the actual seismically driven tsunami began.
“This atmospheric waves event was unprecedented in the modern geophysical record,” said lead author Matoza, an associate professor at UC Santa Barbara’s Department of Earth Science.
The Hunga volcanic eruption has provided unprecedented insight into the behavior of a variety of atmospheric wave types. “The atmospheric waves were recorded globally across a wide frequency band,” said co-author David Fee at the University of Alaska Fairbanks Geophysical Institute. “And by studying this remarkable dataset we will better understand acoustic and atmospheric wave generation, propagation and recording.
“This has implications for monitoring nuclear explosions, volcanoes, earthquakes and a variety of other phenomena,” Fee continued. “Our hope is that we will be better able to monitor volcanic eruptions and tsunamis by understanding the atmospheric waves from this eruption.”
The researchers were most interested in the behavior of an atmospheric wave known as a Lamb wave, which is the dominant pressure wave produced by the eruption. These are longitudinal pressure waves, much like sound waves, but of particularly low frequency. Such low frequency, in fact, that the effects of gravity must be taken into account. Lamb waves are associated with the largest atmospheric explosions, such as large eruptions and nuclear detonations, though the wave characteristics differ between these two sources. They can last from minutes to several hours.
After the eruption, the waves traveled along Earth’s surface and circled the planet in one direction four times and in the opposite direction three times, the authors recorded. This was the same as scientists observed in the 1883 Krakatau eruption. The Lamb wave also reached into Earth’s ionosphere, rising at 700 mph to an altitude of about 280 miles.
“Lamb waves are rare. We have very few high-quality observations of them,” Fee said. “By understanding the Lamb wave, we can better understand the source and eruption. It is linked to the tsunami and volcanic plume generation and is also likely related to the higher-frequency infrasound and acoustic waves from the eruption.”
The Lamb wave consisted of at least two pulses near the volcano. The first had a seven- to 10-minute pressure increase followed by a second and larger compression and subsequent long pressure decrease.
A major difference between the accounts of Hunga’s Lamb waves versus Krakatau’s is the amount and quality of data scientists were able to gather. “We have more than a century of advances in instrumentation technology and global sensor density,” Matoza said. “So the 2022 Hunga event provided an unparalleled global dataset for an explosion event of this size.”
Scientists noted other findings about atmospheric waves associated with the eruption, including remarkable long-range infrasound — sounds too low in frequency to be heard by humans. Infrasound arrived after the Lamb wave and was followed by audible sounds in some regions.
Audible sounds reached Alaska, about 6,200 miles from the volcano, where they were heard around the state as repeated booms. “I heard the sounds,” Fee recalled, “but at the time definitely did not think it was from a volcanic eruption in the South Pacific.”
The scientists believe the sounds heard in Alaska couldn’t have originated in Hunga. While there’s still much to learn, it’s clear that standard sound models cannot explain how audible sounds propagated over such extreme distances. “We interpreted that they were generated somewhere along the path by nonlinear effects,” Matoza explained.
“There is a long list of possible follow-up studies examining the many different aspects of these signals in more detail,” he said. “As a community, we will be working further on this event for years.”
(This release was co-authored by Rod Boyce at University of Alaska Fairbanks’
Geophysical Institute)
JOURNAL
Science
ARTICLE TITLE
Atmospheric waves and global seismoacoustic observations of the January 2022 Hunga eruption, Tonga
ARTICLE PUBLICATION DATE
12-May-2022
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