An undersea volcano erupted in January near the peaceful nation of Tonga and sent huge pressure waves into Earth’s atmosphere, where they repeatedly swept across the planet. The last volcano to generate such large ripples in the atmosphere was Krakatau in 1883, during one of the most destructive volcanic eruptions in recorded history, according to a new study.
“This atmospheric wave event was unprecedented in modern geophysical records,” said first author Robin Matoza, associate professor in the Department of Earth Sciences at the University of California, Santa Barbara. The research, published Thursday, May 12 in the journal Sciencerevealed that the pressure pulse generated by Tonga volcano was “comparable in magnitude to that of the 1883 Krakatau eruption and an order of magnitude greater than that of 1980 Mount St. Helens eruption,” Matoza told Live Science in an email. The higher the amplitude of a wave, the more powerful it is.
A second study, also published on May 12 in Science, suggested that this powerful pulse not only shook the atmosphere, but also sent ripples across the ocean below. In fact, the atmospheric waves generated small, fast-moving meteotsunamis – that is, a series of waves driven by disturbances in atmospheric pressure – which reached the shore hours before conventional tsunamis caused by earthquakes generated by the explosion of the volcano.
These small “precursor” tsunamis have been observed all over the world, mainly in the Pacific Ocean, but also in the Atlantic Ocean and the Mediterranean Sea, surprisingly, said Tatsuya Kubota, a researcher at the National Research Institute on Earth Science and Disaster Resilience in Japan and first author of the second study. “The height of the ‘precursor’ tsunamis…was about a few centimeters, although it depends on the location,” Kubota told Live Science in an email.
An extremely energetic eruption
The Tonga Volcano – called Hunga Tonga-Hunga Ha’apai, or simply Hunga – lies about 65 kilometers northwest of Tonga’s capital, Nuku’alofa. It is one of 12 known submarine volcanoes in the Tonga-Kermadec volcanic arc, a geological feature that runs along the western edge of the Pacific plate of the Earththe crust, according to the Smithsonian’s Global Volcanism Program.
When Hunga erupted in mid-January, the resulting plume of gas and particles hit the mesosphere – the third layer of the atmosphere above Earth’s surface – making it the largest volcanic plume in the satellite record. the amount of energy released during the eruption was comparable to what could be generated by exploding 4 to 18 megatons of TNT, or more than 100 Hiroshima-scale bombs exploding at the same time.
Following the record-breaking eruption, Matoza and a team of more than 70 scientists from 17 countries set out to document the atmospheric waves generated by the explosion. To do this, they pulled data from numerous ground and space-based monitoring systems that had recorded the eruption as it unfolded.
The team found that, of all the atmospheric waves produced by the explosion, the so-called Lamb waves stood out as the most important. Lamb waves run along the Earth’s surface and are similar to sound waves in that they produce vibrations in the medium they pass through. However, Lamb waves propagate at extremely low frequencies, “where the effects of gravity become important,” Matoza said.
Researchers rarely record Lamb waves because they only come from huge explosions in the atmosphere, on the scale of large volcanic eruptions and nuclear tests. “They’re not usually seen for small volcanic eruptions,” Matoza told Live Science.
At their highest, the Lamb waves generated by the Hunga eruption had an amplitude of 280 miles (450 km), meaning they hit the ionosphere – a dense layer of electrically charged particles that lies about 35 to 620 miles (60 to 1,000 km) above the surface of the planet. Over the course of six days, these waves radiated outward from the volcano site, circling the Earth four times in one direction and three times in the other. Based on historical data, the 1883 Krakatau eruption generated Lamb waves that circled the Earth the same number of times, the researchers reported.
The team’s Lamb wave observations align with earlier models of the Hunga eruption that were produced by Nedjeljka Žagar, professor of theoretical meteorology at the University of Hamburg, and colleagues. “We were able to simulate the Hunga Tonga Lamb wave just two days after the event,” and now the new scientific study has provided more details on how these waves spread, using various geophysical measurements, Žagar told Live Science. in an email.
In their own scientific study, Kubota and his colleagues linked these Lamb waves to the fastest tsunamis observed after the eruption. The timing of the Lamb waves and the “precursor” tsunamis seemed to coincide, they found. What is striking is that these precursor waves landed more than two hours earlier than expected for conventional tsunamis, which are largely caused by sudden deformations of the seafloor.
In addition to huge Lamb waves and fast-moving tsunamis, the Hunga eruption also produced incredibly long sound waves and infrasonic waves — meaning acoustic waves of too low a frequency for humans to hear, Matoza reported. and his colleagues. Prominent Lamb waves led the pack, followed by infrasonic waves, then audible sound waves. Remarkably, audible sounds, consisting of repeated short “booms”, were reported across Alaska more than 6,200 miles (10,000 km) from the Hunga eruption.
Originally posted on Live Science.
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