The Hunga Tonga-Hunga Haʻapai volcanic eruption which happened on January 15 2022, has broken another record, knocking the previous record holder, Mount Pinatubo in the Philippines, off the top spot for highest plume ever recorded. Hunga Tonga-Hunga Haʻapai reached heights of 57 kilometers (34 miles), more than 17 kilometers (11 miles) clear of the previous record holder.
Recorded by satellite imagery, the plume is so big that it required an entirely novel approach to be able to record its size. In most cases, to measure the height of a volcano plume, the temperature is taken at the top and then compared with standard air temperatures found at different altitudes. Plumes are normally in the troposphere, the lowest level of Earth’s atmosphere where the temperature decreases with increasing height.
However, this is the first recorded instance of a volcano plume reaching the mesosphere, the area of the atmosphere which is more commonly associated with shooting stars. The mesosphere is the third layer of the atmosphere, approximately between 48 and 90 kilometers (30-56 miles) high. Here, the air temperatures become an unreliable indicator, as they can begin to increase again with higher altitudes. Therefore the team had to come up with a new method.
Based on a phenomenon called the the "parallax effect" – which explains why objects appear to change position when viewed from different lines of sight – the method involved using three geostationary weather satellites 36,000 kilometers (22,369 miles) up in space, and applying the parallax effect to the images the satellites captured. During the eruption the satellites recorded images every ten minutes, allowing the team to observe the changes in the trajectory of the plume.
"It’s the first time we’ve ever recorded a volcanic plume reaching the mesosphere," said Dr Simon Proud, a National Centre for Earth Observation senior scientist at the University of Oxford and RAL Space, in a statement seen by IFLScience. ‘Krakatau in the 1800s might have done as well, but we didn’t see that in enough detail to confirm.
The team now plan to develop an automated system to work out the heights of other volcano plumes using this new method.
"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”, said co-author Dr Andrew Prata from the University of Oxford’s Department of Atmospheric, Oceanic & Planetary Physics.
The study is published in Science.