When the Hengja Tonga-Hung Habai volcano erupted underwater on January 15, about 40 miles north of the capital Tonga, it sent a tsunami and sonic boom that engulfed the world — twice.
The eruption sent long plumes of water vapor into the stratosphere, which lies between 8 and 33 miles (12 and 53 kilometers) above Earth’s surface. That’s enough to fill 58,000 Olympic-sized swimming pools, according to NASA satellite observations.
It was detected by the Microwave Limb Sounder on NASA’s Aura satellite. These satellites measure water vapor, ozone and other atmospheric gases. After the volcano erupted, scientists were shocked by the steam measurement.
They estimate the volcanic eruption released 146 teragrams of water into the stratosphere. One teragram is equal to one trillion grams, which in this case is equal to 10% of the water already in the stratosphere.
The amount of water vapor that reached the stratosphere after the 1991 eruption of Mount Pinatubo in the Philippines has almost quadrupled.
“We’ve never seen anything like it,” said Louis Millan, atmospheric scientist at NASA’s Jet Propulsion Laboratory in Southern California, in a statement. “We had to check carefully to make sure all measurements on the rods were reliable.”
Earth observation
The Microwave Limb Sounder can measure and detect natural microwave signals from Earth’s atmosphere and through thick ash clouds.
“MLS is the only instrument that has a lid that is tight enough to capture volcanic vapor, and is the only instrument that is not affected by the ash ejected from the volcano,” Millan said.
The Ora satellite was launched in 2004 and has since measured only two volcanic eruptions that sent large amounts of steam into the atmosphere. But steam from the 2008 Kasadochi event in Alaska and the 2015 Calbuco eruption in Chile dissipated very quickly.
Tonga’s eruptions are different in that they can trap heat from the steam released into the atmosphere, increasing surface temperatures. According to the researchers, excess water vapor can remain in the stratosphere for years.
The extra water vapor in the stratosphere can also trigger chemical reactions that temporarily deplete Earth’s protective ozone layer.
Explosive anatomy
Fortunately, the warming effect of water vapor is expected to be small and temporary and will disappear as the excess moisture recedes. Researchers believe that this will not be enough to worsen the current conditions as a result of the climate crisis.
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Researchers believe that the depth of the volcano’s caldera, which is 490 feet (150 meters) below sea level, is the main reason for the large amount of steam.
If it were too deep, the depth of the ocean would dampen the eruption, it would be too shallow, and the amount of seawater heated by rising magma would not match that reaching the stratosphere, the researchers said.
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