The Tonga eruption seen from space. Credit: NASA/NOAA
When the Tonga volcano erupted beneath the South Pacific, it did what this type of volcanoes do: it blasted seawater, ash, and gas into the sky with terrifying force. But then it did something that scientists didn’t expect at all. The drifting plume appears to have turned into a kind of high-altitude chemical reactor, breaking down methane for more than a week.
This is all the more stunning because methane is a potent greenhouse gas, far more potent than carbon dioxide.
Many, Many Cows
The “eye in the sky” satellites spotted a strange signal coming from the long-lived plume. The plume was rich in formaldehyde, a short-lived gas that forms when methane breaks apart. Formaldehyde usually survives for only a few hours in sunlit air. But this cloud lingered for days as it drifted across the Pacific toward South America.
Simply put, this was a clear tell that the eruption’s clouds were constantly wiping out the methane.
“When we analysed the satellite images, we were surprised to see a cloud with a record-high concentration of formaldehyde,” Dr. Maarten van Herpen of Acacia Impact Innovation BV explained. “We were able to track the cloud for 10 days, all the way to South America. Because formaldehyde only exists for a few hours, this showed that the cloud must have been destroying methane continuously for more than a week.”
The team used TROPOMI, an instrument aboard the European Space Agency’s Sentinel-5P satellite. In the paper, the researchers report formaldehyde levels as high as 12 parts per billion at about 30 kilometers altitude (unusually high for the stratosphere). The researchers estimate that the eruption destroyed around 900 metric tons of methane per day.
In total, the volcano eliminated the amount of methane that two million cows would produce in a year.
Image taken from a video of the eruption on January 15, 2022. Credit: Tonga Geological Services.
That does not mean the volcano “solved” its own climate impact. The methane destruction was small compared with the total amount eliminated by the volcano, but it was large enough for satellites to see, and the process itself makes the discovery very interesting.
×
Thank you! One more thing…
Please check your inbox and confirm your subscription.
The Chemistry Behind the Process
The chemistry began with Tonga’s unusual setting. Hunga Tonga-Hunga Ha’apai was a submarine volcano, sitting roughly 150 meters below the ocean surface. When it erupted, it hurled salty seawater upward along with ash and volcanic gases.
Some of that material rose more than 30 kilometers above Earth’s surface. Parts of the plume reached even higher. The eruption also injected a massive amount of water vapor into the stratosphere, increasing the stratospheric water burden by about 10%.
Inside that plume, the researchers think sunlight struck ash particles coated with sulfate, iron, and salt. The reaction may have released chlorine atoms. These are tiny, highly reactive fragments that can attack methane and start breaking it apart.
“What is new, and completely surprising, is that the same mechanism appears to occur in a volcanic plume high up in the stratosphere, where the physical conditions are entirely different,” Professor Matthew Johnson of the University of Copenhagen said.
The process resembles one scientists had seen before over the Atlantic Ocean. Dust from the Sahara can mix with sea spray, and sunlight can turn that mixture into chlorine chemistry. Tonga seems to have carried a similar recipe far higher into the atmosphere.
The authors are careful not to treat this as normal volcano behavior. Tonga had the right ingredients in the right place: seawater, ash, and intense sunlight at rare altitude. Most eruptions may not produce the same reaction.
A Possible Yardstick for Methane Removal
Satellite image using the VIIRS satellite on 16 January 2022, showing in blue the cloud of formaldehyde measured by TROPOMI. To the left is the Australian coast of Queensland. Credit: van Herpen et al.
Methane is one of the biggest near-term climate targets. It’s responsible for about a third of current warming, and over 20 years it traps roughly 80 times more heat than carbon dioxide. But unlike CO2, methane usually breaks down within about a decade.
That short life has made methane removal tempting. Some researchers imagine reactors that pull methane from air. Others study open-air chemistry. But researchers still need to answer the same stubborn question: how can they prove the methane disappeared?
“How do you prove that methane has been removed from the atmosphere? How do you know your method works? It’s very difficult,” Dr. Jos de Laat of the Royal Netherlands Meteorological Institute noted. “But here we address that problem by showing that methane breakdown can in fact be observed using satellites.”
Methane (CH4), is much more potent but also much more short-lived than carbon dioxide.
But, formaldehyde can also come from fires and other sources, so researchers must separate methane’s chemical trail from background noise. In this case, the plume rose over the ocean, where direct satellite methane measurements are harder, but ultraviolet measurements of formaldehyde can still work.
“Retrieving formaldehyde from TROPOMI in a stratospheric volcanic plume is far outside the instrument’s standard operating conditions—we had to carefully correct the satellite’s sensitivity for the unusual altitude of the signal and account for interference from the high sulfur dioxide concentrations,” Dr. Isabelle De Smedt of the Royal Belgian Institute for Space Aeronomy said. “Getting these corrections right was essential to confirm that what we were seeing was real.”
Johnson framed the discovery cautiously. “It’s an obvious idea for industry to try to replicate this natural phenomenon, but only if it can be proven to be safe and effective,” he told The Brighter Side of News.
The study was published in the journal Nature Communications.
