On January 15, Tonga-Hunga Ha’apai volcano erupted under the sea, shaking the South Pacific and a tsunami around the world. The eruption was the most powerful ever recorded, causing an atmospheric shock wave that circled the globe four times and sent a plume of debris more than 50 kilometers into the atmosphere. But it didn’t stop there. Ash and gases spewing into the sky also shot billions of kilograms of water into the atmosphere, a new study concludes. This water is likely to remain there for years, where it could eat away at the ozone layer and possibly warm the Earth.
“The idea that an eruption could directly inject large amounts of water vapor into the stratosphere has not, to my knowledge, been directly observed, at least not to this extent,” says Matthew Toohey, a physicist who focuses on climate modeling and volcanic eruption effects at the University of Saskatchewan and was not involved in the work. “We’re really surprised by this eruption in a lot of different ways.”
The study comes thanks to the Microwave Limb Sounder (MLS) aboard NASA’s Aura satellite. The instrument, which was commissioned in 2004, measures various compounds in the Earth’s atmosphere at altitudes of 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, was the water and sulfur dioxide released by the eruption because these compounds can affect the climate. With repeated observations from MLS both on the day of the eruption and in the days after, scientists were able to track the plume and its water content as it grew and dispersed around the globe.
In total, the plume shot about 146 billion kilograms of water into Earth’s stratosphere, the dry layer of the atmosphere that begins a few miles above sea level, the authors report this month in Geophysical Research Letters. That’s the equivalent of about 58,000 Olympic swimming pools, or about 10% of the total water content in 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. This is likely due to the size of the eruption and its underwater location, he says. Water is likely to remain in the stratosphere for half a decade or more, he says.
Large volcanic eruptions often cool the climate because the sulfur dioxide they release forms compounds that reflect incident sunlight. But with so much water vapor spewed into the air, Tonga’s eruption could have a different impact. Water absorbs energy coming from the Sun, making it a powerful greenhouse gas. And sulfur dioxide dissipates within a few years, while water is likely to stick around for at least 5 years — and potentially longer, Millán thinks.That could cause the Earth to warm for years and accelerate greenhouse gas warming, Toohey says. “Let’s jump ahead a few years.But the true effects on climate will likely take some time to understand, says Allegra LeGrande, a physics research scientist at NASA’s Goddard Institute for Space Studies who was not involved in the work. “I don’t think there’s a consensus on what the overall impact will be.”
High above Earth, water is likely to react with other chemicals, potentially degrading the ozone layer that protects us from ultraviolet light and even altering the circulation of air currents that control weather.As climate impacts unfold, scientists are anxiously awaiting even more new insights from a volcanic eruption unlike any they’ve seen. “It’s exciting to see these new measurements,” says LeGrande. “It’s exciting to see something we haven’t seen before.”
Reference: https://www.science.org/content/article/massive-undersea-eruption-filled-atmosphere-water
