Massive undersea eruption filled atmosphere with water

On 15 January, Tonga’s Hunga Tonga-Hunga Ha'apai volcano erupted under the sea, rocking the South Pacific nation and sending tsunamis racing around the world. The eruption was the most powerful ever recorded , causing an atmospheric shock wave that circled the globe four times, and sending a plume of debris more than 50 kilometers into the atmosphere. But it didn’t stop there.

The ash and gasses punching into the sky also shot billions of kilograms of water into the atmosphere, a new study concludes. That water will likely remain there for years, where it could eat away at the ozone layer and perhaps even warm Earth.

“The idea that an eruption could directly inject a large amount of water vapor into the stratosphere has not to my knowledge been directly observed, at least not to this magnitude,” says Matthew Toohey, a physicist who focuses on climate modeling and the effects of volcanic eruptions at the University of Saskatchewan and was not involved with the work. “We are really surprised by this eruption in many different ways.”

The study comes thanks to the Microwave Limb Sounder (MLS) aboard NASA’s Aura satellite. The instrument, which became operational in 2004, measures a variety of compounds in Earth’s atmosphere at heights up to about 100 kilometers. Of particular interest to scientists at NASA’s Jet Propulsion Laboratory, including study co-author and JPL atmospheric scientist Luis Millán, were the water and sulfur dioxide released by the eruption, because those compounds can affect climate. With repeated observations from the MLS on both the day of the eruption and the days afterward, the researchers were able to watch the plume, and its water content, grow and disperse around the globe.

In all, the plume shot approximately 146 billion kilograms of water into Earth’s stratosphere , an arid layer of the atmosphere that begins several miles above sea level, the authors report this month in Geophysical Research Letters . That’s equivalent to about 58,000 Olympic-size swimming pools, or about 10% of the entire water content of the stratosphere, Millán says.

Other volcanoes have added measurable amounts of water vapor to Earth’s atmosphere, he says, but the scale this time was unprecedented. That’s likely because of the eruption’s magnitude and underwater location, he says. The water will probably remain in the stratosphere for half a decade or more, he says.

Big volcanic eruptions often cool the climate, because the sulfur dioxide they release forms compounds that reflect incoming sunlight. But with so much water vapor flung aloft, the Tonga eruption could have a different impact. Water absorbs incoming energy from the Sun, making it a potent greenhouse gas. And the sulfur dioxide will dissipate in just a few years whereas the water will likely stick around for at least 5 years—and potentially longer Millán thinks.

NASA Earth Observatory/Joshua Stevens and Lauren Dauphin

That could make Earth warmer for years and accelerate the warming from greenhouse gasses, Toohey says. “We’ll kind of just jump forward by a few years.”

But the actual effects on climate will likely take time to understand, says Allegra LeGrande, a physical research scientist at NASA’s Goddard Institute for Space Studies who was not involved with the work. “I don’t think there is a consensus about what the overall impact will be.”

High above Earth, the water will likely react with other chemicals, potentially degrading the ozone layer that protects us from ultraviolet light, and even changing the circulation of air currents that govern weather patterns.

As the climatic impacts unfold, scientists are eagerly awaiting even more new insights from a volcanic eruption that’s proved to be unlike any other they’ve seen. “It’s exciting seeing these new measurements,” LeGrande says. “It’s exciting seeing something we haven’t seen before.”