Hunga Tonga-Hunga Ha’apai eruption releases largest volcanic plume ever recorded : ScienceAlert

Hunga Tonga-Hunga Ha’apai eruption releases largest volcanic plume ever recorded : ScienceAlert

A spectacular and explosive volcanic eruption in January 2022 produced the largest plume of steam and ash in recorded history.

The towering column that grew out of Hunga Tonga-Hunga Ha’apai reached an enormous height of 57 kilometers (35 miles) above sea level.

That height makes it the first ever seen volcanic eruption to completely breach the stratosphere and breach the mesosphere.

“It’s a remarkable result because we’ve never seen a cloud of any kind this high before,” says atmospheric scientist Simon Proud University of Oxford.

Perhaps this should come as no surprise: the eruption was one of the largest volcanic eruptions mankind has ever seen. But accurately measuring the height of his feathers required some clever detective work.

The height of a volcanic plume is usually estimated from the temperature profile measured by infrared-observing satellites. Because thermal emission, or heat, produces infrared radiation, these satellites can detect volcanic clouds.

As plumes extend through the troposphere (that’s the atmospheric layer closest to Earth, the one we live in), they lose heat, so the temperature of the top of the plume can be used to estimate height.

However, when the plume reaches the stratosphere, at an average height of ca 12 kilometers, this strategy loses accuracy as the temperature profile of the plume changes again, this time becoming warmer. So a team of researchers led by Prada took a different approach.

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The researchers still relied on satellite data, but the measurement was based on parallax. If you’ve ever closed one eye after another and watched nearby objects shift from side to side relative to their background, you’ve seen parallax in action.

It is the difference between the apparent position of two objects seen along different lines of sight, and it is the basis of depth perception in binocular vision. Our brain processes the information from each eye and calculates the distance to the objects seen. We can use parallax to calculate all kinds of distances.

To obtain parallaxes of the Hunga Tonga-Hunga Ha’apai eruption, the researchers used data from three geostationary weather satellites that observed the event from different positions in low Earth orbit, taking images every 10 minutes.

From this, Proud and his team calculated that the plume reached a height of 57 kilometers. Interestingly, this is very close to the height of 58 kilometers calculated by NASA scientists back in January using data from two geostationary satellites.

Previously, the highest volcanic cloud was Mount Pinatubo in the Philippines; its 1991 eruption produced a plume that extended to 40 kilometers in altitude.

Hunga-Tonga’s much higher cloud height is a bit puzzling, however, given that Mount Pinatubo’s eruption was of similar strength: both eruptions registered as a 6 on the Volcanic Explosivity Index (VEI) scale.

However, there is a simple answer to this question. If the Hunga-Tonga cloud had been measured using the Mount Pinatubo technique, the maximum height would have been placed at about 39 kilometers.

Even if Mount Pinatubo’s plume reached higher than measured, we still don’t know the mechanisms for reaching that height. So that could be a fun topic to explore.

We also don’t know how a volcanic plume of that height would affect the mesosphere; since no other volcanic plume was observed so high, the effects were only indirect.

A hazy substance was observed at the top of the Hunga-Tonga cloud; what it is and how long it will stay up there is unknown.

This means there is more work to be done to help us understand this fascinating and devastating event.

“We would also like to apply this technique to other eruptions and develop a dataset of plume heights that volcanologists and atmospheric scientists can use to model the dispersion of volcanic ash in the atmosphere,” says atmospheric physicist Andrew Prata University of Oxford.

“Further scientific questions we would like to understand are: Why did the Tonga plume go so high? What will the climate impacts of this eruption be? And what exactly did the plume consist of?”

The research was published in Science.

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