Tonga volcanic eruption is strongest in over a century

Scientists have begun to piece together what happened during the January 15 eruption of the Hunga Tonga-Hunga Ha’apai submarine volcano about 65 kilometers (40 miles) north of Tonga’s capital which killed at least three people. The eruption defied easy explanation and upended scientists’ understanding of this type of volcano.
The volcanic eruption sent rarely seen pressure waves around the globe for six days and triggered an unexpected type of tsunami wave, according to two new studies published Thursday in the journal Science. The huge plume of gas, water vapor and dust also created hurricane-force winds in space, NASA said in a separate study released this week.

Early data in the aftermath of the explosion suggested it was the largest since the eruption of Mount Pinatubo in the Philippines in 1991, but the scientific studies, which involved 76 scientists in 17 countries, suggested that the pressure waves it unleashed were similar to those generated by the cataclysmic Krakatoa eruption of 1883 and 10 times larger than those of 1980 Eruption of Mount St. Helens in Skamania County, Washington.

Tonga’s eruption was “unusually energetic”, the Science study researchers wrote. Low-frequency atmospheric pressure waves, called Lamb waves, detected after the eruption circled the planet four times in one direction and three times in the opposite direction, they revealed.

A relatively rare phenomenon, these waves propagate at the speed of sound. They are not detectable by humans and are slower than shock waves because they have sometimes been incorrectly described, said study author Quentin Brissaud, a geophysicist to the Norwegian Seismic Network in Oslo. Lamb waves were also seen during the Cold War after atmospheric nuclear testing.

“It’s quite rare. So Lamb waves are really related to large air volume displacements. And they mostly propagate along the Earth’s surface,” said co-author Jelle Assink, geophysicist Principal at the Department of Seismology and Acoustics of the Royal Netherlands Meteorological Institute.

Moving across the surface of several oceans and seas, Lamb pressure waves from the explosion created a rapid wave of scattered tsunamis.

Traditional tsunamis are usually related to sudden changes in the ocean floor, such as during an earthquake. Basically, these so-called meteotsunamis move much faster than traditional tsunamis, arriving two hours earlier than expected and lasting longer, which could have implications for early warning systems.

And because an atmospheric pressure wave generated them, the tidal waves appeared to “jump continents”, with tsunamis recorded from the Pacific to the Atlantic, said co-author Silvio De Angelis, professor of Geophysics of Volcanoes at the Department of Earth, Ocean and Ecological Sciences at the University of Liverpool in the UK.

The research also revealed that the audible sound of the eruption was detected more than 10,000 kilometers (6,000 miles) from the source in Alaska. — where it was heard as a series of booms. Krakatoa’s 1883 eruption was heard 4,800 kilometers (2,980 miles) away, the study found, although it was less consistently reported than Tonga’s.

A lithograph depicts clouds pouring from Krakatoa volcano during the cataclysmic 1883 eruption in southwestern Indonesia.

The researchers said more data was needed to understand the mechanism of the eruption.

It is believed that one of the reasons for such an energetic explosion – creating a 30 kilometer high (about 19 miles) umbrella cloud and a plume about 58 kilometers high (36 miles) – was because “a magma hot and gas-laden came into contact with (seawater) very quickly,” De Angelis said by email. “The rapid transfer of intense heat between hot magma and cold water causes violent explosions capable of tearing the magma.”

Spatial Disruption

Another study, published Tuesday in Geophysical Research Letters, found that the Tonga volcano has also wreaked havoc in space, causing hurricane-force winds, based on data from NASA’s Ionospheric Connection Explorer mission, or ICON, and European Space Agency Swarm satellites.
The giant plume of gas, water vapor and dust pushed into the sky by the eruption created significant pressure disturbances in the atmosphere, driving strong winds, NASA said in a statement. As these winds expanded upwards into thinner layers of the atmosphere, they began to move faster.

“Reaching the ionosphere and the outer reaches of space, ICON recorded wind speeds of up to 450 mph, making them the strongest winds below 120 miles measured by the mission since its launch,” NASA said.

(Left to right) Satellite images from January 6 and 18 show the impact of the volcanic eruption near Tonga.

In the ionosphere, where Earth’s atmosphere meets space, extreme winds also jolted electric currents, knocking particles from their usual eastward-flowing electric current – called the equatorial electrojet – to an eastward direction. west for a short time, and the electrojet surged. five times its normal peak power.

“It’s very surprising to see the electrojet being strongly inverted by something that happened on the Earth’s surface,” said Joanne Wu, a physicist at the University of California, Berkeley and co-author of the novella. Geophysical Research Letters study.

“This is something we’ve only seen before with strong geomagnetic storms, which are a form of weather in space caused by particles and radiation from the sun.”

Brian Harding, a UC Berkeley physicist and lead author, said the Tonga eruption “allowed us to test the poorly understood link between the lower atmosphere and space”.

He added: “The volcano has created one of the greatest disturbances in space we have seen in the modern age.”

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