When the Hengja Tonga-Hung Hapai volcano erupted under the sea on January 15, 40 miles (65 kilometers) north of Tonga’s capital, it caused a tsunami as well as a sonic boom that rippled around the world — twice.
The explosion sent a long plume of water vapor into the stratosphere, which lies between 8 and 33 miles (12 and 53 kilometers) above Earth’s surface. The water was enough to fill 58,000 Olympic-sized swimming pools, according to revelations from a NASA satellite.
It was detected by the Microwave Limb Sounder on NASA’s Aura satellite. The satellite measures water vapor, ozone, and other atmospheric gases. After the eruption of the volcano, scientists were surprised by the water vapor readings.
They estimate that the volcanic eruption delivered 146 teragrams of water into the stratosphere. One teragram equals one trillion grams, and in this case, it was equal to 10% of the water already in the stratosphere.
That’s nearly four times the amount of water vapor that reached the stratosphere after the 1991 eruption of Mount Pinatubo in the Philippines.
“We’ve never seen anything like this before,” study author Lewis Millan, an atmospheric scientist at NASA’s Jet Propulsion Laboratory in Southern California, said in a statement. “We had to carefully check all the measurements in the shaft to make sure they were trustworthy.”
The Microwave Limb Sounder can measure and detect natural microwave signals from Earth’s atmosphere even through thick ash clouds.
“The MLS was the only instrument with sufficiently dense coverage to capture the plume of water vapor as it occurred, and the only instrument unaffected by the ash emitted by the volcano,” Millan said.
The Ora satellite was launched in 2004 and since then has only measured two volcanic eruptions that sent water vapor into the atmosphere in large quantities. But the water vapor from the 2008 Kasatochi event in Alaska and the 2015 Calbuco eruption in Chile dissipated fairly quickly.
The Tonga eruption was different because the water vapor it sent into the atmosphere can trap heat, which can cause surface temperatures to rise. According to the researchers, excess water vapor can remain in the stratosphere for several years.
Additional water vapor in the stratosphere can also lead to chemical reactions that temporarily contribute to the depletion of Earth’s protective ozone layer.
Fortunately, the warming effect of water vapor is expected to be small and temporary, and will dissipate as the excess vapor diminishes. Researchers don’t think it will be enough to exacerbate current conditions due to the climate crisis.
The researchers believe that the main reason for the high amount of water vapor was due to the depth of the volcano’s caldera 490 feet (150 meters) below the ocean surface.
If it was too deep, the researchers said, the depth of the ocean would have muffled the eruption, it would have been too shallow, and the amount of seawater heated by the rising magma wouldn’t have matched what had reached the stratosphere.