This volcanic eruption reached so high it depleted the ozone layer

The Hunga Tonga-Hunga Ha’apai eruption in January 2022 was so intense that it partially depleted Earth’s ozone layer in the following weeks — marking the first time on record that scientists observed such a rapid and strong decrease of ozone miles above our heads resulting from volcanic activity, according to a study released Thursday in the journal Science.

A team of international scientists found ozone concentrations in the stratosphere (10 to 25 miles high) decreased by as much as 30 percent in spots shortly after the eruption. Overall, they measured concentrations depleted by around 5 percent across the Indian and Pacific Ocean two weeks following the eruption.

“It’s much more difficult for an eruption to impact this region because it has to be very explosive to reach” that high, said Stephanie Evan, lead author of the study. “That was the case with Hunga Tonga because it was able to eject things up to 50 kilometers (30 miles).”

The ozone layer is located in Earth’s stratosphere. At these higher altitudes, ozone acts as a sun shield to protect us from harmful ultraviolet radiation. (Ozone near the planet’s surface can irritate our lungs.) The team - which includes researchers from NASA and the National Oceanic and Atmospheric Administration (NOAA) in the United States to the French remote Réunion Island - said this depletion is not likely to affect ultraviolet radiation or people’s health, but the results unveil a new aspect of how volcanoes can interact with our upper atmosphere.

“This was never really documented before,” said Evan, adding that there wasn’t an eruption able to reach that altitude during the satellite era, which spans only recent decades.

On the evening of Jan. 15, the underwater volcano erupted in the southwest Pacific and sent atmospheric shock waves around the world multiple times. Residents on one of the islands of Tonga reported hearing blasts shortly before 5 p.m. local time from the volcano, which was located about 40 miles away. Within 30 minutes, volcano plumes rose into the atmosphere like a gargantuan umbrella. The eruption triggered large tsunami waves, including some that reached 45 feet, and caused four deaths.

As images, videos and ground reports surfaced that day, scientists began scrambling to study arguably the most interesting volcanic eruption in their lifetimes. Researchers found the blast was bigger than any U.S. nuclear explosion. Ash flew up 38 miles into our atmosphere, higher than another volcanic eruption on record. The underwater explosion also sent a record amount of water, enough to fill nearly 60,000 Olympic-size swimming pools, into the stratosphere - again, where the ozone layer is located.

On the day of the eruption, study co-author Karen Rosenlof also began mobilizing equipment and people to study the volcanic plume on the ground. She contacted her colleague Evan, who was based on Réunion Island, which houses one of the most equipped observatories in the southern hemisphere. It also sat right on the pathway of the volcanic plume after the eruption, giving researchers a prime location to study the chemistry of the plume.

“This is the first time we’ve been able to get into a volcanic plume as fresh as this was,” said Rosenlof, a climate scientist at NOAA Chemical Sciences Laboratory. The plume moved over Réunion island in about a week.

Using balloons strapped with scientific instruments, the Réunion team measured changes in several chemicals in the plume. Notably, the team saw changes in water vapor and ozone - which they surmise are linked. They found the largest dips of ozone - including 30 percent on one night - where water vapor concentrations were the highest. As the water vapor dispersed across the globe, the large ozone dips mellowed.

Evan explained that high amounts of water vapor in the stratosphere can break down ozone through chemical reactions. She previously found the eruption increased our global water vapor in the stratosphere by 10 percent. That water reacted with chlorine-containing molecules in the atmosphere and converted them to an active form that can destroy ozone. NASA satellite data confirmed changes in ozone and chlorine concentrations through satellite data.

“We know that volcanic emissions can trigger some chemistry inside the atmosphere, which can destroy ozone. But before these were observed months after a volcanic eruption,” said Evan, an atmospheric scientist at the French National Center for Scientific Research. “What is interesting is the decrease that you’re seeing, at 5 percent, is happening in two weeks.”

Atmospheric scientist Pasquale Sellitto, who was not involved in the research, said he wasn’t surprised that the Tonga eruption affected the ozone layer - but it is a unique observation.

“Once such large amounts of water vapour are in the stratosphere, large and rapid ozone perturbations are also expected, as nicely explained” in the paper, said Sellitto, an associate professor at Paris-Est Créteil University, in an email.

Scientists have seen ozone concentrations decrease after a volcanic eruption - but never at this scale. After the 1991 Mt. Pinatubo eruption, researchers saw ozone concentrations decrease in the tropics at these altitudes, but that was also months after the eruption.

Rosenlof also emphasized that Mt. Pinatubo injected a lot aerosols - not water vapor - into the upper atmosphere, which induce chemical reactions that can deplete ozone. This study, she said, likely marks the first time that anyone has observed how water vapor from a volcano can rapidly affect our ozone layer.

“In terms of ozone reductions due to excess water vapor, it’s been hypothesized, but I’m not sure that it’s actually been measured as directly as it was this time,” Rosenlof said. “This is kind of a test of that mechanism, where we can say this kind of chemistry really does happen in the stratosphere.”

She added the insight from these observations can also teach scientists things that they can then apply to other problems. For instance, if water vapor drastically increases in the atmosphere with climate change - especially in areas with monsoons - some researchers hypothesize that the location could see sustained losses in ozone, which could affect our solar radiation or people’s health.

But the studies with the Tonga eruption continue. Even a year after the eruption, Evan said ozone concentrations in the stratosphere remained lower. Other studies have shown that the volcanic aerosols have affected the local temperature, which can change the winds in the upper atmosphere. She said they’re trying to understand if these ozone changes are related to chemical reactions or changes in transport.

“It is like a huge natural laboratory to test processes associated with the stratospheric composition,” said Sellitto.