Tonga volcano eruption strongest in more than a century

Tonga volcano eruption strongest in more than a century

Scientists have started to figure out what happened during the Jan. 15 eruption of the underwater volcano Hunga Tonga-Hunga Ha’apai about 65 kilometers (40 miles) north of Tonga’s capital, which killed at least three people. The eruption has defied a simple explanation and turned scientists’ understanding of this type of volcano on its head.
The volcanic eruption sent rarely seen pressure waves across 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 cloud of gases, water vapor and dust also created hurricane-force winds in space, NASA said in a separate study released this week.

Early data after the blast suggested it was the largest since Mount Pinatubo in the Philippines erupted in 1991, but the Science studies, which involved 76 scientists in 17 countries, found that the the blast waves they triggered were similar to those generated by the catastrophe Krakatoa eruption of 1883 and ten times larger than that of 1980 Erupting Mount St. Helens in Skamania County, Washington.

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

These waves are a relatively rare phenomenon and propagate at the speed of sound. They are undetectable to humans and are slower than shock waves, which are sometimes incorrectly described, said study author Quentin Brissaud, a geophysicist at the Norwegian Seismic Array in Oslo. Lamb waves were also observed during the Cold War after atmospheric nuclear tests.

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

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The Lamb pressure waves from the blast moved across the surface of several oceans and seas, creating a fast-moving flood of scattered tsunamis.

Traditional tsunamis are usually associated with sudden seafloor changes, such as during an earthquake. Crucially, these so-called meteotsunamis travel much faster than traditional tsunamis, arrive two hours earlier than expected and last longer, which could impact early warning systems.

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

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

A lithograph shows clouds pouring out of the Krakatoa volcano during the cataclysmic 1883 eruption in southwest Indonesia.

The researchers said more data is needed to understand the eruption’s mechanism.

It is believed that one of the reasons for such an energetic explosion – which created an umbrella cloud 30 kilometers high and a plume about 58 kilometers high – was that “hot and gas-laden magma invaded contact with the (seawater) very quickly,” it said De Angelis via email “The rapid transfer of intense heat between hot magma and cold water causes violent explosions that can rupture the magma.”

space disruption

Another study published Tuesday in Geophysical Research Letters found that the Tonga volcano also wreaked havoc in space, unleashing hurricane-force winds, based on data from NASA’s Ionospheric Connection Explorer mission, or ICON, and the Swarm satellites of the European Space Agency.
The huge plume of gases, water vapor and dust thrown into the sky by the eruption caused large pressure disturbances in the atmosphere, resulting in strong winds, NASA said in a statement. As these winds spread up into thinner layers of the atmosphere, they began to move faster.

“Reaching the ionosphere and the edge of space, ICON has measured wind speeds up to 450 miles per hour — making them the strongest sub-120-mile winds recorded by the mission since launch,” NASA said .

(From left) Satellite images from January 6 and 18 show the effects of the volcanic eruption near Tonga.

In the ionosphere, where Earth’s atmosphere meets space, the extreme winds also churned up electrical currents, rotating particles westward from their usual eastward-flowing electrical current—called the equatorial electrojet—for a short time, and the electrojet rose to five times its normal peak power.

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

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

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

He added: “The volcano has caused one of the largest disturbances in space that we have seen in modern times.”

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