Tonga’s volcanic eruption has released the highest plume on record

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WASHINGTON — The powerful Jan. 15 underwater eruption of Tonga’s Hunga Tonga-Hunga Ha’apai volcano in the South Pacific produced a plume that shot higher into Earth’s atmosphere than any on record — about 35 miles (57 km) — as it stretched more than halfway to space, researchers said Thursday.

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The white-gray plume released by the eruption in the Polynesian archipelago became the first documented to have penetrated an icy layer of the atmosphere called the mesosphere, according to scientists who used a new technique using multiple satellite images to measure its height.

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The plume consisted mostly of water with some 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 explosion sent tsunami waves into the Pacific Ocean and produced an atmospheric wave that traveled several times around the world. (See related chart)

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“For me, what was impressive is how quickly the explosion happened. It went from nothing to a 57km high cloud in just 30 minutes. I can’t imagine what it must have been like to see it from the ground,” said Proud, a fellow at Britain’s National Earth Observatory who works at the University of Oxford and STFC RAL Space.

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

Damage and loss of life—six deaths—were relatively low due to the blast’s remote location, although it obliterated a small and uninhabited island. Tonga is an archipelago of 176 islands with a population of just over 100,000, located southeast of Fiji and just west of the International Date Line.

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“It could have been a lot worse,” said Proud.

The plume extended through the lower two layers of the atmosphere, the troposphere and stratosphere, and about 4 miles (7 km) into the mesosphere. The top of the mesosphere is the coldest place in the atmosphere.

“The mesosphere is one of the upper layers of our atmosphere and it’s generally pretty quiet – there’s no familiar weather up there and the air is very dry and extremely thin,” Proud said. “It’s one of the least understood parts of the atmosphere because it’s so hard to get to. Lower, we can use airplanes. Higher up, we have spaceships. Many meteorites burn up in the mesosphere, and it is also home to nocturnal clouds, which are sometimes visible in the summer sky toward the poles.”

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The plume was far from reaching the next atmospheric layer, the thermosphere, which starts about 53 miles (85 km) above the Earth’s surface. A demarcation called the Karman line, about 62 miles (100 km) above the Earth’s surface, is generally considered the boundary with space.

Until now, the highest recorded volcanic plumes were from the 1991 eruption of Mount Pinatubo in the Philippines at 25 miles (40 km) and the 1982 eruption of El Chichón in Mexico at 19 miles (31 km). Volcanic eruptions in the past likely produced higher plumes, but they occurred before scientists could make such measurements. Proud said the 1883 eruption of Krakatau in Indonesia probably reached the mesosphere.

Scientists were unable to use their standard temperature-based technique of measuring a volcanic plume because the January eruption passed the maximum height for which this method could be used. Instead, they turned to three geostationary weather satellites that took images every 10 minutes and relied on what’s called the parallax effect – determining the location of an object by seeing it along multiple lines of sight.

“For the parallax approach we’re using to work, you need multiple satellites in different locations – and that’s only become possible on a global scale in the last decade or so,” Proud said.

(Reporting by Will Dunham Editing by Rosalba O’Brien)