Scientists identify tallest volcanic plume ever recorded

Using images captured by satellites, researchers at the University of Oxford’s Department of Physics and RAL Space have confirmed that the January 2022 eruption of the Hunga Tonga-Hunga Ha’apai volcano produced the highest plume on record. The colossal eruption is also the first directly observed and has broken through to the mesosphere layer of the atmosphere. The results were published today in the journal Science.

On January 15, 2022, Hunga Tonga-Hunga Ha’apai, a submarine volcano in the Tongan archipelago in the South Pacific Ocean, erupted violently. The explosion was one of the most powerful ever observed, shock waves around the world, causing devastating tsunamis that left thousands homeless. A towering column of ash and water was ejected into the atmosphere, but until now scientists have lacked an accurate way to measure how high this was.

Normally, the height of a volcanic Kudos can be estimated by measuring the temperature recorded at the top by infrared-based satellites and comparing it to a vertical reference temperature profile. This is because in the troposphere (the first and lowest layer of the Earth’s atmosphere), the temperature decreases with height. But if the eruption is so large that the plume penetrates the next layer of the atmosphere (the stratosphere), this method becomes ambiguous because the temperature starts to rise again with altitude (because the ozone layer absorbs ultraviolet radiation from the sun).

To solve this problem, the researchers used a new method based on a phenomenon called “the parallax effect.” This is the apparent difference in an object’s position when viewed from multiple lines of sight. You can see this for yourself by closing your right eye and extending one hand with the thumb up. Then when you switch eyes so that your left side is closed and your right side is open, your thumb seems to shift slightly against the background. By measuring this apparent change in position and combining it with the known distance between your eyes, you can calculate the distance to your thumb.

The Tonga volcano’s location is covered by three geostationary weather satellites, so the researchers were able to apply the parallax effect to the aerial photos they captured. Crucially, the satellites themselves recorded images every 10 minutes during the eruption, documenting the rapid changes in the plume’s orbit.

The results showed that the plume reached a height of 57 kilometers at its highest point. This is significantly higher than the previous record holders: the 1991 eruption of Mount Pinatubo in the Philippines (40 km at the highest point) and the 1982 eruption of El Chichón in Mexico (31 km). It also makes the plume the first observational evidence of a volcanic eruption that injects material through the stratosphere and directly into the mesosphere, which begins about 50 km above the Earth’s surface.

Lead author Dr. Simon Proud (University of Oxford, RAL Space and the National Center for Earth Observation), said: “It is an extraordinary result, as we have never seen such a high cloud. In addition, the ability to measure the height as 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.”

The Oxford researchers now plan to build an automated system to calculate the height of volcanic plumes using the parallax method. Co-author Dr. Andrew Prata of the Atmospheric, Oceanic & Planetary Physics subsection added: “We want to apply this technique to other eruptions as well and develop a dataset of plume heights that can be used by volcanologists and atmospheric scientists to model the distribution of volcanic ash in the atmosphere. Further scientific questions we would like to understand are: Why did the Tonga plume go so high? What will be the climate effects of this eruption? And what exactly did the plume consist of?”

In addition to the University of Oxford, the study also involved the Rutherford Appleton Laboratory and the National Center for Earth Observation in Harwell and the University of Applied Sciences in Munich. The newspaper “The January 2022” eruption from Hunga Tonga-Hunga Ha’apai volcano reached the mesosphere” is published in Science.