The 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 magnitude shook the Earth.
Robin Matoza of UC Santa Barbara led a team of 76 scientists, from 17 countries, to characterize the atmospheric waves of the eruption, the strongest recorded on a volcano since the eruption of Krakatau in 1883. The work of the eruption he team, compiled in an unusually short period of time, details the size of the waves from the eruption, which the authors say were comparable to those of Krakatau. The data also provides exceptional resolution of the evolving wavefield compared to what was available from the historic event.
The article, published in the journal Scienceis the first complete account of the atmospheric waves of the eruption.
Early evidence suggests an eruption on January 14 sank the volcano’s main vent below sea level, triggering the massive explosion the following day. The January 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 earthquake-driven tsunami began.
“This atmospheric wave event was unprecedented in modern geophysical records,” said lead author Matoza, an associate professor in the Department of Earth Sciences at UC Santa Barbara.
The Hunga volcanic eruption provided unprecedented insight into the behavior of a variety of atmospheric wave types. “Atmospheric waves have been recorded globally over a wide band of frequencies,” said co-author David Fee of the University of Alaska’s Fairbanks Geophysical Institute. “And by studying this remarkable dataset, we will better understand the generation, propagation and recording of acoustic and atmospheric waves.
“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 that eruption.”
The researchers were most interested in the behavior of an atmospheric wave known as the Lamb wave, which is the dominant pressure wave produced by the eruption. They are longitudinal pressure waves, much like sound waves, but of particularly low frequency. A frequency so low, in fact, that the effects of gravity have to be taken into account. Lamb waves are associated with the largest atmospheric explosions, such as large flares and nuclear detonations, although the characteristics of the waves differ between these two sources. They can last from a few minutes to several hours.
After the eruption, the waves scoured the Earth’s surface and circled the planet four times in one direction and three times in the opposite direction, the authors reported. It was the same thing scientists observed when Krakatau erupted in 1883. The Lamb wave also reached Earth’s ionosphere, rising at 700 mph to an altitude of about 280 miles.
“Lamb waves are rare. We have very few high-quality sightings of them,” Fee said. “By understanding the Lamb wave, we can better understand the source and the eruption. It is related to the generation of the tsunami and the volcanic plume and is also likely related to the high frequency infrasound and acoustic waves of the eruption. “
The Lamb wave consisted of at least two pulses near the volcano. The first had a 7-10 minute pressure rise followed by a second larger squeeze and a long subsequent pressure drop.
A major difference between the accounts of the lamb waves from Hunga and those from Krakatau is the amount and quality of data the scientists were able to gather. “We have over a century of advances in instrumentation technology and overall sensor density,” Matoza said. “Thus, the 2022 Hunga event provided an unprecedented global data set 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 for humans to hear. 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 across the state as repeated booms. “I heard the sounds,” Fee recalls, “but at the time I certainly didn’t think it was from a volcanic eruption in the South Pacific.”
Scientists believe that the sounds heard in Alaska cannot come from Hunga. Although there is still much to learn, it is clear that standard sound models cannot explain how audible sounds travel over such extreme distances. “We interpreted that they were generated somewhere along the way by nonlinear effects,” Matoza explained.
“There is a long list of possible follow-up studies looking in more detail at the many different aspects of these signals,” he said. “As a community, we will continue to work on this event for years to come.”
Tonga Islands: Seismic algorithm reveals magnitude of January 2022 eruption
Robin S. Matoza, Atmospheric Waves and Global Seismoacoustic Observations of the January 2022 Hunga Eruption, Tonga, Science (2022). DOI: 10.1126/science.abo7063. www.science.org/doi/10.1126/science.abo7063
Provided by University of California – Santa Barbara
Quote: Massive eruption of tongan volcano provides burst of atmospheric wave data (May 12, 2022) Retrieved May 12, 2022 from https://phys.org/news/2022-05-massive-eruption-tongan-volcano- explosion.html
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