When the Hengja Tonga-Hung Hapai volcano erupted under the sea on January 15, 65 kilometers north of the capital, Tonga, it caused a tsunami and a sonic boom that spread across the world — twice.
The explosion sent a long cloud of water vapor into the stratosphere, between 12 and 53 kilometers above the Earth’s surface. The water was enough to fill 58,000 Olympic swimming pools, NASA has revealed.
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 volcano erupted, scientists were surprised by the water vapor readings.
They estimate that the volcanic eruption released 146 teragrams of water into the stratosphere. A teragram equals a trillion grams, and in this case it was equal to 10% of the water already in the stratosphere.
This is nearly four times the amount of water vapor that reached the stratosphere after the eruption of Mount Pinatubo in the Philippines in 1991.
“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 well to make sure they were reliable.”
The microwave probe can measure and detect natural microwave signals from Earth’s atmosphere, even through thick ash clouds.
“The MLS was the only instrument with sufficient coverage to capture the plume of water vapor as it occurred, and the only instrument unaffected by the ash from the volcano,” Millan said.
The Ora satellite was launched in 2004 and has since measured only two volcanic eruptions that have 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 quickly dissipated.
The Tonga eruption was different because water vapor flowing into the atmosphere can trap heat, which can warm the surface. 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 heating effect of water vapor is expected to be small and temporary, and it will dissipate as the excess vapor recedes. The researchers do not believe that it would be sufficient to exacerbate 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, 150 meters below the surface of the ocean.
If it had been too deep, the researchers said, the depth of the ocean would have sunk in the eruption, and it would have been too shallow, and the amount of seawater heated by the rising magma wouldn’t match what had reached the stratosphere.
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