The Hunga volcano ushered in 2022 with a bang, devastated the island nation of Tonga and sent 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 eruption’s atmospheric waves, the strongest recorded from a volcano since the 1883 Krakatoa eruption. The team’s work, compiled in a unusually short time, describes the size of the waves that spawned from the eruption, which the authors found to be comparable to Krakatoa’s. The data also provides exceptional resolution of the evolving wavefield compared to what was available from the historical event.
The article, published in the magazine Scienceis the first comprehensive account of the eruption’s atmospheric waves.
Early evidence suggests that an eruption on January 14 sunk the volcano’s main vent below sea level, triggering the massive explosion the next 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 seismically-driven tsunami started.
“This atmospheric wave event was unprecedented in the modern geophysical record,” said lead author Matoza, an associate professor in UC Santa Barbara’s Department of Earth Science.
The Hunga volcanic eruption has provided unprecedented insight into the behavior of different atmospheric wave types. “The atmospheric waves were recorded worldwide over a wide frequency band,” said co-author David Fee of the Fairbanks Geophysical Institute at the University of Alaska. “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. “We hope we can better 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, the dominant pressure wave produced by the eruption. These are longitudinal pressure waves, just like sound waves, but with a very low frequency. So low, 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, although the wave characteristics differ between these two sources. They can last from a few minutes to several hours.
After the eruption, the waves traveled along Earth’s surface, orbiting the planet four times in one direction and three times in the opposite direction, the authors wrote. This was the same as scientists observed in the Krakatoa eruption in 1883. The Lamb wave also reached the Earth’s ionosphere, rising at 700 mph to a height of about 280 miles.
“Lamb waves are rare, we have very few high-quality observations of them,” Fee said. “Understanding the Lamb wave will help us better understand the source and the eruption. It is linked to the tsunami and the formation of volcanic plumes and is probably also related to the higher-frequency infrasound and acoustic waves of the eruption. “
The Lamb wave consisted of at least two pulses near the volcano. The first had a pressure increase of 7 to 10 minutes, followed by a second and greater compression and subsequent long pressure decrease.
A major difference between the reports of Hunga’s Lamb waves and those of Krakatoa is the amount and quality of data scientists were able to collect. “We have made more than a century of progress in instrumentation technology and global sensor density,” said Matoza. “So the Hunga event in 2022 provided an unparalleled global data set for an explosion event of this magnitude.”
Scientists have noted other findings about atmospheric waves linked to the eruption, including notable long-range infrasound — sounds too low 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,” recalls Fee, “but I certainly didn’t think it was from a volcanic eruption in the South Pacific at the time.”
The scientists believe that the sounds heard in Alaska could not have originated in Hunga. While much remains to be learned, it is clear that standard sound models cannot explain how audible sounds propagate over such extreme distances. “We interpreted them to be generated somewhere along the path by nonlinear effects,” Matoza explained.
“There is a long list of possible follow-up studies that examine the many different aspects of these signals in more detail,” he said. “As a community, we will continue to work on this event for years to come.”
Tonga Islands: A seismic algorithm reveals the magnitude of the January 2022 eruption
Robin S. Matoza, Atmospheric Waves and Global Seismoacoustic Observations of the Hunga Eruption in January 2022, 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 causes explosion of atmospheric wave data (2022, May 12) retrieved May 12, 2022 from https://phys.org/news/2022-05-massive-eruption-tongan-volcano- explosion.html
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