Tonga underwater volcanic eruption produced the highest plume on RECORD, study reveals
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The Tonga volcanic eruption in January produced the highest ever recorded plume, scientists have confirmed.
Hunga Tonga-Hunga Ha’apai, an underwater volcano in the South Pacific, released an ash cloud that was 187,000 feet (57 km/35 miles) high.
Its colossal eruption on January 15 this year was also the first recorded to have broken through into the third layer of the atmosphere – the mesosphere.
The mesosphere starts about 160,000 feet (48 km) above us, and is where passing meteors start to burn up and form shooting stars.
Researchers from the University of Oxford and RAL Space used three geostationary weather satellites to accurately measure the massive plume’s height.
The previous record-holder, the 1991 eruption of Mount Pinatubo in the Philippines, caused a plume that was recorded as 131,000 feet (40 km/ 25 miles) high.
‘It’s an extraordinary result as we have never seen a cloud of any type this tall before,’ said lead author Dr Simon Proud.
‘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.’
Parallax-based retrievals of plume altitude at 04:30 GMT on 15 January 2022 overlaid on Himawari-8 data for the same time frame
WHAT IS THE ‘PARALLAX EFFECT’?
The parallax effect is the difference in the apparent location of an object viewed along two different lines of sight.
You can see this effect by closing your right eye, and holding out one hand with the thumb raised upwards.
If you then switch eyes, so that your left is closed and your right is open, your thumb will appear to shift slightly against the background.
Astronomers use this effect to measure large distances, like between the Earth and stars.
The parallax effect
The Hunga Tonga-Hunga Ha’apai eruption took place in the southern Pacific Ocean, around 40 miles (65km) from Tonga’s main island.
It triggered a 7.4 magnitude earthquake, sending tsunami waves crashing into the island that were 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 blasted 20,000 Olympic swimming pools-worth of water into the stratosphere.
For the study, published today in Science, scientists wanted to accurately measure how far the towering column of ash and water produced stretched into the atmosphere.
Normally, this is done by measuring the temperature of the top of the plume using infrared-based satellites and comparing it to standard temperatures at different 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 went into the third layer of the atmosphere, the mesosphere.
Due to the ozone layer absorbing solar ultraviolet radiation, temperatures in the stratosphere and mesosphere actually increase with height.
So, to measure the plume, Dr Proud’s team developed a different technique that utilises the ‘parallax effect’ – the difference in the apparent location of an object viewed along two different lines of sight.
This technique allows researchers to calculate the distance between the object and both viewers.
The location of the Tonga volcano is covered by three weather satellites, all 22,000 miles (36,000 km) up in space – the GOES-17 from the US, Himawari-8 from Japan and GeoKompSat-2A from South Korea.
Aerial shots taken by these satellites of known location were used to gauge the plume’s height.
On top of that, they recorded images every ten minutes, meaning 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 altitude over time. Infrared (IR) heights are derived from Himawari-8 satellite measurements and known temperature standards from the European Centre for Medium-Range Weather Forecasts. The blue lines indicate altitudes estimated by the stereoscopic method across the entire plume, and the green markers are parallax heights derived from a manual analysis of data from 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 estimation for the Mount Pinatubo eruption could 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 went the highest – it fell between two of the satellite images and we missed it.’
The researchers now intend to construct an automated system to compute the heights of volcano plumes using the parallax method.
They hope that a dataset of plume heights will help other scientists model the dispersion of volcanic ash in the atmosphere.
The Hunga Tonga-Hunga Ha’apai eruption took place in the southern Pacific Ocean, around 40 miles (65km) from the country’s main island
Its colossal eruption on January 15 this year was the first recorded to have broken through into the third layer of the atmosphere – the mesosphere. It also caused many effects, like atmospheric waves, extreme winds and unusual electric currents, that were felt around the world and into space
The previous record-holder, the 1991 eruption of Mount Pinatubo in the Philippines, caused a plume that was recorded as 131,000 feet (40 km/ 25 miles) high (pictured)