The volcanic eruption in Tonga in January produced the highest plume ever recorded, scientists have confirmed.
Hunga Tonga-Hunga Ha’apai, an underwater volcano in the South Pacific, spewed an ash cloud 187,000 feet (57 km/35 miles) high.
Its colossal eruption on January 15 this year was also the first on record to break through the third layer of the atmosphere – the mesosphere.
The mesosphere begins about 160,000 feet (48 km) above us, and is where passing meteors begin to burn up and form shooting stars.
Researchers from the University of Oxford and RAL Space used three geostationary weather satellites to precisely measure the height of the massive plume.
The previous record holder, the 1991 eruption of Mount Pinatubo in the Philippines, produced a plume recorded as 131,000 feet (40 km/25 miles) high.
“It is an outstanding result as we have never seen such a high cloud of any type before,” said lead author Dr Simon Proud.
“Furthermore, the ability to estimate height the way we did, with the parallax method, is only possible now that we have good satellite coverage.
“That wouldn’t have been possible a decade or so ago.”
Parallax-based retrievals of plume height at 04:30 GMT on 15 January 2022 superimposed on Himawari-8 data for the same timeframe
WHAT IS THE ‘PARALLAX EFFECT’?
The parallax effect is the difference in the apparent location of an object seen along two different lines of sight.
You can see this effect by closing your right eye and holding out one hand with the thumb up.
If you then switch eyes, so that your left is closed and your right is open, your thumb will appear slightly offset against the background.
Astronomers use this effect to measure great distances, such as between the Earth and the stars.
The parallax effect
The Hunga Tonga-Hunga Ha’apai eruption took place in the South Pacific, about 65 km from the main island of Tonga.
It triggered a 7.4-magnitude earthquake and sent tsunami waves crashing into the island felt as far away as Russia, the United States and Chile.
The eruption released more energy than the Tsar Bomba – the most powerful nuclear bomb ever detonated – and blew 20,000 Olympic swimming pools’ worth of water into the stratosphere.
For the study, published today in Science, researchers wanted to accurately measure how far the tall column of ash and water produced extended into the atmosphere.
Normally, this is done by measuring the temperature at the top of the plume using infrared-based satellites and comparing it to standard temperatures at various known altitudes.
This can be done because previous plumes have only extended into the troposphere, the first layer of the atmosphere, where temperature decreases with height.
However, the Hunga Tonga-Hunga Ha’apai cloud entered the third layer of the atmosphere, the mesosphere.
Because the ozone layer absorbs the sun’s ultraviolet radiation, the temperature of the stratosphere and mesosphere actually increases with altitude.
So, to measure the plume, Dr Proud’s team developed another technique that uses the ‘parallax effect’ – the difference in the apparent location of an object seen along two different lines of sight.
This technique allows researchers to calculate the distance between the object and both observers.
The location of the Tonga volcano is covered by three weather satellites, all 22,000 miles (36,000 km) up in space – GOES-17 from the USA, Himawari-8 from Japan and GeoKompSat-2A from South Korea.
Aerial photographs taken by these satellites of known location were used to measure the height of the plume.
On top of that, they recorded images every ten minutes, which meant the researchers could document rapid changes in the plume’s trajectory.
Dr Proud said: ‘Thirty years ago, when Pinatubo erupted, our satellites were nowhere near as good as they are now. They could only scan the Earth every 30 minutes. Or maybe even every hour.
Evolution of volcanic plume height over time. Infrared (IR) heights are derived from Himawari-8 satellite measurements and known temperature standards from the European Center for Medium-Range Weather Forecasts. The blue lines indicate heights estimated by the stereoscopic method over the entire plume, and the green markers are parallax heights derived from a manual analysis of data from the Himawari-8, GK-2A and GOES-17 satellites
An animation showing the evolution of the height of the Hunga Tonga-Hunga Ha’apai eruption plume, measured using the stereoscopic method applied to images from three weather satellites.
Dr. Proud also speculates that the estimate for the Mount Pinatubo eruption may be incorrect as a result of the reduced satellite data available at the time.
He said: “We think for Pinatubo we actually missed the peak of the activity and the points where it was at its highest – it fell between two of the satellite images and we missed it.”
The researchers now intend to construct an automated system to calculate the height of volcanic plumes using the parallax method.
They hope that a dataset of plume heights will help other researchers model the distribution of volcanic ash in the atmosphere.
The Hunga Tonga-Hunga Ha’apai eruption took place in the South Pacific, about 40 miles (65 km) from the country’s main island
Its colossal eruption on January 15 this year was the first recorded to break through the third layer of the atmosphere – the mesosphere. It also caused many effects, such as atmospheric waves, extreme winds and unusual electrical currents, which were felt around the world and into space
The previous record holder, the 1991 eruption of Mount Pinatubo in the Philippines, produced a plume recorded as 131,000 feet (40 km/25 miles) high (pictured)
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