When the Hunga Tonga-Hunga Ha’apai volcano, 40 miles (65 kilometers) north of Tonga’s capital, erupted underwater on Jan. 15, it created a tsunami and a sonic boom that shook the world twice.
The eruption sends water vapor high into the stratosphere, which is between 8 and 33 miles (12 and 53 kilometers) above the Earth’s surface. According to detections from a NASA satellite, this water was enough to fill 58,000 Olympic-sized swimming pools.
The detection was made by the Microwave Limb Sounder on NASA’s Aura satellite. The satellite measures water vapor, ozone and other atmospheric gases. After the eruption, scientists were surprised by the indicators of water vapor.
According to their calculations, the 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 present in the stratosphere.
This is 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,” said study author Luis Millan, an atmospheric scientist at NASA’s Jet Propulsion Laboratory in Southern California. “We had to carefully check all the measurements in the plume to make sure they were reliable.”
Keeping an eye on the earth
Microwave Limb Sound can measure natural microwave signals from Earth’s atmosphere and detect them even through thick ash clouds.
“MLS was the only instrument that had a dense enough cover to capture the moment the water vapor plume occurred and was unaffected by the ash emitted by the volcano,” Millan said.
The Aura satellite was launched in 2004, and since then it has measured only two volcanic eruptions, which raised very high levels of water vapor into the atmosphere. 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 could trap heat, causing the surface to warm. According to the researchers, excess water vapor can remain in the stratosphere for several years.
The extra water vapor in the stratosphere can also cause chemical reactions that temporarily deplete the Earth’s protective ozone layer.
Anatomy of an eruption
Fortunately, the warming effect of water vapor is expected to be small and temporary, and dissipate as the additional vapor subsides. Researchers do not believe that this will be enough to worsen the current conditions due to the climate crisis.
Researchers believe that the main reason for the high amount of water vapor is due to the depth of the volcano’s caldera, which is 490 feet (150 meters) below the surface of the ocean.
If it were too deep, the depth of the ocean would silence the eruption, and if it were too shallow, the amount of seawater heated by the erupting magma would not be the same as that reaching the stratosphere, the researchers said.
