Giant volcanic eruption of Tonga was as powerful as Krakatoa in 1883, scientists have found

(ORDO NEWS) — An underwater volcano erupted in January near the Pacific island of Tonga and sent powerful pressure waves into the Earth’s atmosphere, where they circled the planet several times.

The last volcano to cause such large ripples in the atmosphere was Krakatoa in 1883, during one of the most destructive volcanic eruptions in recorded history, a new study shows.

“This atmospheric wave event was unprecedented in the modern geophysical record,” said first author Robin Matoza, assistant professor of earth sciences at the University of California, Santa Barbara.

A study published Thursday (May 12) in the journal Science found that the pressure pulse created by the Tonga volcano was “comparable in amplitude to the Krakatoa eruption of 1883 and an order of magnitude larger than the 1980 eruption of Mount St. Helens,” said Matosa via email Live Science.

The higher the amplitude of the wave, the more powerful it is.”

The second study, also published May 12 in the journal Science, suggests that this powerful impulse not only stirred up the atmosphere, but also sent ripples across the ocean below.

In fact, atmospheric waves generated small, fast-moving meteorological tsunamis – that is, a series of waves caused by disturbances in air pressure – that hit the coast several hours before the usual, seismically driven tsunamis generated by a volcano explosion.

These small “harbingers” of tsunamis have been observed around the world, mainly in the Pacific Ocean, but also in the Atlantic Ocean and the Mediterranean Sea, which is surprising, said Tatsuya Kubota, a researcher at the National Research Institute for Geosciences and Disaster Resilience in Japan. and first author of the second study.

The height of the tsunami ‘harbingers’ … was about a few centimeters or so, although it depends on the location,” Kubota.

Volcano Tonga – called Hunga-Tonga-Hunga-Ha’apai, or simply Hunga – is about 40 miles (65 km) northwest of the Tongan capital of Nuku’alofa.

It is one of 12 known submarine volcanoes in the Tonga-Kermadec Volcanic Arc, a geological structure that runs along the western edge of the Pacific Plate, according to the Smithsonian Global Volcanism Program.

When Hunga erupted in mid-January, the resulting plume of gas and particles entered the mesosphere – the third layer of the atmosphere above the Earth’s surface – and became the largest volcanic plume on satellite record.

The amount of energy released by the eruption was comparable to what could be obtained from an explosion of 4 to 18 megatons of TNT or from the simultaneous explosion of more than 100 Hiroshima-sized bombs.

After the record-breaking eruption, Matosa and a group of more than 70 scientists from 17 countries set themselves the task of documenting what atmospheric waves were generated by the explosion.

To do this, they collected data from numerous ground and space monitoring systems that recorded the eruption at the time of its occurrence.

The team found that of all the atmospheric waves generated by the explosion, the so-called Lamb waves stand out as the most noticeable. Lamb waves propagate along the Earth’s surface and are similar to sound waves in that they create vibrations in the medium they pass through.

However, Lamb waves propagate at extremely low frequencies, “where the effect of gravity becomes significant,” Matosa said.

Researchers rarely record Lamb waves because they only occur in huge explosions in the atmosphere, on the scale of large volcanic eruptions and nuclear tests. “They are usually not seen in small volcanic eruptions,” Matosa.

The amplitude of the highest Lamb waves generated by the Hung eruption was 280 miles (450 km), that is, they hit the ionosphere – a dense layer of electrically charged particles that is at an altitude of 35 to 620 miles (60 to 1000 km) above the planet’s surface .

For six days, these waves radiated outward from the volcano, circumnavigating the Earth four times in one direction and three times in the other.

Based on historical data, the Krakatoa eruption in 1883 generated Lamb waves that circled the Earth the same number of times, the researchers said.

The team’s observations of the Lamb waves are consistent with earlier models of the Hung eruption event, which were created by Nezelka ┼Żagar, professor of theoretical meteorology at the University of Hamburg, and her colleagues.

“We were able to model the Hunga-Tonga-Lamba wave just two days after the event,” and now a new Science study has provided more details on how these waves propagated using various geophysical measurements, Jagar.

In their own study in Science, Kubota and colleagues connected the dots between these Lamb waves and the fastest tsunamis seen since the eruption. They found that the time of occurrence of the Lamb waves and the “harbingers” of the tsunami coincides.

Strikingly, these precursor waves made landfall more than two hours earlier than would be expected for normal tsunamis, which are mainly caused by sudden deformations of the seafloor.

In addition to huge Lamb waves and fast-moving tsunamis, the Hung eruption also generated incredibly long-range sound waves and infrasonic waves – acoustic waves too low a frequency to be heard by humans, Matosa and his colleagues said.

Prominent Lamb waves led the group, followed by infrasonic waves and then sound waves.

Notably, audible sounds consisting of short, repetitive “booms” have been recorded across Alaska, more than 6,200 miles (10,000 km) from the Hunga eruption.

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