An areal shot of a large plume of gray ash over a blue ocean.

Tongan volcano eruption triggered ‘highest plume on record’

The powerful underwater eruption of Tonga’s Hunga Tonga-Hunga Ha’apai volcano earlier this year produced a plume that soared higher into Earth’s atmosphere than any other on record, experts say.

Researchers say the plume reached about 57 kilometers into the sky, spanning more than half the space.

The greyish-white plume triggered by the eruption became the first documented record to have penetrated an icy layer of the atmosphere called the mesosphere, according to scientists who used multiple satellite images to measure its height.

Its plume was composed mostly of water, with ash and sulfur dioxide mixed in, said atmospheric scientist Simon Proud, lead author of the research published in the journal Science.

Eruptions from terrestrial volcanoes tend to have more ash and sulfur dioxide and less water.

The deafening January 15 eruption sent tsunami waves across the Pacific Ocean and produced an atmospheric wave that circled the globe several times.

A large dust explosion above water
The January volcano eruption triggered a tsunami warning for several South Pacific island nations.(Reuters: NOAA/CIRA/Handout)

“For me, what was impressive was how quickly the eruption happened. It went from nothing to a 57 km high cloud in just 30 minutes. I can’t imagine what that must have been seeing from the ground,” Mr. Proud said.

“What fascinated me was the dome-shaped structure in the center of the umbrella plume. I’ve never seen anything like it before,” added Andrew Prata, atmospheric scientist from Oxford and co- author of the study.

Damage from the eruption wiped out a small nearby uninhabited island and resulted in the deaths of six residents.

Its plume extended through the two lower layers of the atmosphere, the troposphere and the stratosphere, and about 7 km into the mesosphere. The top of the mesosphere is the coldest place in the atmosphere.

The plume was far from reaching the next atmospheric layer, the thermosphere, which begins about 85 km above the Earth’s surface.

A boundary called the Karman Line, about 100 km above the Earth’s surface, is generally considered the boundary with space.

The scientists used three geostationary weather satellites which acquired images every 10 minutes to measure the explosion and relied on what is called the parallax effect: determining the position of something by viewing it along multiple lines of sight.

“For the parallax approach we use to work, you need multiple satellites in different locations – and it’s only been in the last decade that this has become possible on a global scale,” Proud said. .

So far, the highest recorded volcanic plumes have come from the 1991 eruption of Mount Pinatubo in the Philippines, 40 km away, and the 1982 eruption of El Chichón in Mexico, 31 km away.

Past volcanic eruptions have likely produced larger plumes, but occurred before scientists could make such measurements.

Reuters

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