When the undersea volcano Hunga Tonga-Hunga Ha’pai erupted on January 15, 40 miles (65 km) north of Tonga’s capital, it created a tsunami as well as a sonic boom that reverberated twice around the world.
The eruption sends a plume of water vapor into the stratosphere, which is between 8 and 33 miles (12 and 53 km) above the Earth’s surface. That was enough water to fill 58,000 Olympic-size swimming pools, according to data from NASA satellites.
This was detected by the Microwave Limb Sounder instrument on NASA’s Aura satellite. Satellites measure water vapor, ozone and other atmospheric gases. After the eruption, scientists were surprised by the water vapor readings.
They estimate that the eruption delivered 146 teragrams of water into the stratosphere. One teragram is equivalent to one trillion grams, and in this case, equals 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 it,” study author Louise Millan, an atmospheric scientist at NASA’s Jet Propulsion Laboratory in Southern California, said in a statement. “We had to carefully inspect all the measurements of the plume to make sure they were reliable.”
Keeping an eye on the world
The Microwave Limb Sounder instrument can measure natural microwave signals from Earth’s atmosphere and detect them even through thick ash clouds.
“MLSE was the only instrument with coverage thick enough to capture water vapor ice, and the only instrument unaffected by volcanic ash,” Milan said.
The Aura satellite was launched in 2004 and since then it has measured only two volcanic eruptions that pumped significant amounts of water vapor high into the atmosphere. But water vapor from the 2008 Kasatochi event in Alaska and the 2015 Calbuco eruption in Chile spread rather quickly.
Tonga’s eruption was different because the water vapor it released into the atmosphere could trap heat, which could have caused warmer surface temperatures. According to the researchers, the excess water vapor can remain in the stratosphere for several years.
Excess water vapor in the stratosphere can also cause chemical reactions that temporarily contribute to the depletion of Earth’s protective ozone.
Anatomy of an explosion
Fortunately, the warming effect of water vapor is expected to be small and temporary and dissipate as the excess vapor recedes. Researchers do not believe this will be enough to exacerbate the current climate crisis.
Researchers believe that the depth of the volcano’s caldera is the main reason for the high water vapor content 490 feet (150 m) below sea level.
If it was too deep, the depth of the ocean would have changed the eruption, and if it was too shallow, the amount of seawater heated by the erupting magma would not match what reached the stratosphere, the researchers said.