On January 15, 2022, Hunga Tonga–Hunga Haʻapai – an underwater volcano in the Tongan archipelago in the southern Pacific Ocean – violently erupted, sending powerful shockwaves around the world and triggering devastating tsunamis. Until recently, scientists have been unable to reliably measure how tall the towering column of ash and water (the volcanic plume) that was ejected into atmosphere was.
Now, by using satellite-based images, a team of researchers from the University of Oxford has discovered that this volcano produced the highest-ever recorded plume, which has broken through to the mesosphere layer of the atmosphere.
Usually, since in the troposphere (the atmosphere’s lowest layer), temperature decreases with height, how tall a volcanic plume is can be estimated by measuring the temperature recorded at its top and comparing it to a reference vertical temperature profile. However, if the eruption is so large that that the plume penetrates into the next atmospheric layer (the stratosphere), this method becomes unreliable because the temperature begins again to increase with height, due to the ozone layer absorbing UV solar radiation.
To overcome this problem, the scientists used a new method based on a phenomenon called “the parallax effect” (the apparent difference in an object’s position when viewed from multiple perspectives). Since the location of the Tonga volcano is covered by three geostationary weather satellites, the researchers were able to apply the parallax effect to the aerial images these satellites captured.
The analysis revealed that the plume reached an altitude of 57 kilometers, which is significantly higher than previously documented eruptions, such as the 1991 eruption of Mount Pinatubo in the Philippines (40 km), and the 1982 eruption of El Chichón in Mexico (31 km).
“It’s an extraordinary result as we have never seen a cloud of any type this tall before. Furthermore, the ability to estimate the height in the way we did (using the parallax method) is only possible now that we have good satellite coverage. It wouldn’t have been possible a decade or so ago,” said study lead author Simon Proud, a research fellow in Satellite Data Analysis at Oxford.
“We’d also like to apply this technique to other eruptions and develop a dataset of plume heights that can be used by volcanologists and atmospheric scientists to model the dispersion of volcanic ash in the atmosphere,” added study co-author Andrew Prata, a postdoctoral fellow in Atmospheric Physics at the same university. “Further science questions that we would like to understand are: Why did the Tonga plume go so high? What will be the climate impacts of this eruption? And what exactly was the plume composed of?”
The study is published in the journal Science.
Image Credit: Simon Proud / Uni Oxford, RALSpace NCEO / Japan Meteorological Agency
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By Andrei Ionescu, Earth.com Staff Writer