A spectacular and explosive eruption of a volcano in January 2022 produced the highest plume of steam and ash in recorded history.
The towering plume that originated from Hunga Tonga-Hunga Ha’apai reached a whopping 57 kilometers (35 miles) above sea level.
This altitude makes it the first-ever volcanic eruption seen to have completely breached the stratosphere to penetrate the mesosphere.
“It’s an unusual finding because we’ve never seen a cloud of any kind this long before,” says atmospheric scientist Simon Proud of the University of Oxford.
Perhaps this should come as no surprise: the volcanic eruption was one of the largest volcanic eruptions humanity has ever experienced. But accurately measuring the height of its shaft took some clever detective work.
The height of a volcanic plume is usually estimated based on the temperature profile measured by satellites that take infrared observations. Since thermal emissions, or heat, produce infrared radiation, these satellites can detect volcanic plumes.
As the plumes extend through the troposphere (which is the layer of the atmosphere closest to Earth, the layer we live in), they lose heat, so the temperature of the top of the plume can be used to estimate the height.
However, once the column reaches the stratosphere, at an average altitude of about 12 kilometers, this strategy loses accuracy because the column’s temperature profile changes again, this time getting warmer. Therefore, a team of researchers led by Proud took a different approach.
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The researchers still relied on data from satellites, but the measurement was based on parallax. If you’ve closed one eye after another and seen objects near you appear to move from side to side compared to their background, you’ve seen the view in action.
It is the difference between the apparent position of two objects along different lines of vision, and is the basis for depth perception in binoculars. Our brain processes information from each eye and determines the distance to objects in view. We can use parallax to calculate all kinds of distances.
To obtain parallax measurements of the Hunga Tonga-Hunga Ha’apai volcano eruption, the researchers used data from three geostationary weather satellites that monitored the event from different locations in low Earth orbit, and took pictures 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 58 km altitude that NASA scientists calculated in January using data from two geostationary satellites.
Previously, the highest recorded volcanic plume was Mount Pinatubo in the Philippines; Its 1991 eruption produced a plume that extended up to 40 kilometers in height.
However, the much greater height of the Hunga Tonga plume is a bit puzzling, given that Mount Pinatubo’s eruptions were similar in strength: both eruptions were recorded as 6 on the Volcanic Explosive Index (VEI) scale.
However, there is an easy answer to this question. If the Hengja-Tonga plume had been measured using Mount Pinatubo techniques, the maximum height would have been set at about 39 kilometres.
Even if Mount Pinatubo’s plume reached higher than the measurement, we still don’t know what the mechanisms were for reaching that height. So it can be a fun topic to explore.
Nor do we know how a volcanic plume of this height could affect the mesosphere. Since no other volcanic plume reaching this height was observed, the effects were only indirect.
A misty substance is observed at the top of the Hongga-Tonga plume; What this is, and how long it will last there, is unknown.
This means that there is more work to be done to help us understand this wonderful and devastating event.
“We would also like to apply this technique to other volcanic eruptions and develop a data set of plume heights that can be used by volcanologists and atmospheric scientists to model the dispersal of volcanic ash in the atmosphere,” says atmospheric physicist Andrew Prata of the University of Oxford.
“More scientific questions we would like to understand are: Why did the Tonga plume rise so high? What are the climatic effects of this volcanic eruption? What exactly was the plume formed?”
The search was published in Sciences.
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