The eruption of the undersea volcano Hengja Tonga-Hung Hapai earlier this year sent so much water vapor into the atmosphere that it likely temporarily warmed the Earth’s surface, according to observations by a NASA satellite. This temporary point will not greatly affect the climate of our planet, but it shows how huge the volcanic eruption really was.
The volcano erupted on January 15, about 40 miles (65 kilometers) north of the capital of Tonga (more than 4,000 kilometers east of the coast of Australia), causing a tsunami and sonic boom that rippled around the world twice. The explosion sent a plume of water vapor into the stratosphere, a layer of the atmosphere, with enough water to fill 58,000 Olympic-size swimming pools, according to NASA.
The phenomenon was so massive that it was detected by the Microwave Limb Sounder (MLS) instrument on NASA’s Aura satellite, which measures ozone, water vapor and other atmospheric gases. Scientists estimate that the eruption sent 146 teragrams of water into the stratosphere. This equals about 10% of the water already in the atmosphere.
“We’ve never seen anything like it before,” Luis Millan, an atmospheric scientist at NASA’s Jet Propulsion Laboratory in Southern California, said in a statement. Milan led research looking into the amount of water vapor that the volcano sends out. “We had to carefully check all the measurements in the column to make sure they were reliable,” he added.
Volcanic eruptions rarely release much water. NASA began making measurements 18 years ago, and since then, only two other eruptions (the 2008 Kasatucci event in Alaska and the 2015 Calbuco eruption in Chile) have sent off significant amounts of water vapor. But those did not come close to the Tonga event, and the water vapor quickly dissipated.
In general, water makes volcanic eruptions more explosive, so you’d expect an explosive event like Tonga to have a lot of water, but nonetheless, it was surprising to see how much water was released from the eruption into the atmosphere. In this case, not only was the water from the volcano itself what the researchers discovered, but the water was evaporated from the ocean around the volcano.
It usually takes two to three years for aerosols from volcanoes to fall from the stratosphere. But the water from the Tonga eruption could take five to ten years to dissipate, according to the researchers. Given this time frame and the amount of water, it would be the first recorded volcanic eruption to affect the climate through surface warming.
The planet has already warmed by 1.1°C since the start of the Industrial Revolution and is set to continue to warm. Fortunately, the effect of water vapor from the volcano is expected to be small and temporary, and it should not exacerbate our climate problems.
The authors of the new study also explain that the main cause of the massive amount of water vapor was the depth of the volcano’s caldera: 150 meters (490 feet) below the surface. If it were too shallow, the amount of seawater heated by the magma would not have matched what reached the stratosphere, and if it was too deep, the depth of the ocean would have limited the eruption.
The MLS instrument was used to detect water vapor due to its ability to monitor the natural microwave signals emitted from the atmosphere. By measuring these signals, the MLS can see through obstructions such as ash clouds that can blind other devices and focus on water vapor. For Milan, it was the “only instrument” with coverage dense enough to capture the plume of water vapor, and it’s a good tool to help us understand extreme events such as the Tonga eruption.
The study was published in the journal Geophysical Research Letters.