When the underwater volcano Hunga Tonga-Hunga Ha’apai erupted 40 miles (65 kilometers) north of Tonga’s capital on January 15, it created a tsunami and sonic boom that traveled around the world — twice.
The eruption sent a high plume of water vapor into the stratosphere, which is between 8 and 33 miles (12 and 53 kilometers) above Earth’s surface. According to NASA satellite records, there was enough water to fill 58,000 Olympic-sized swimming pools.
Detection was by the Microwave Limb Sounder instrument on NASA’s Aura satellite. The satellite measures water vapour, ozone and other atmospheric gases. After the eruption, scientists were surprised by the water vapor readings.
They estimate the eruption pumped 146 teragrams of water into the stratosphere. One teragram equals one trillion grams, and in this case it equaled 10% of the water already in the stratosphere.
That’s almost four times the amount of water vapor released into the stratosphere after the 1991 eruption of Mount Pinatubo in the Philippines.
“We’ve never seen anything like it,” study author Luis Millán, an atmospheric scientist at NASA’s Jet Propulsion Laboratory in Southern California, said in a statement. “We had to carefully examine all measurements in the cloud to ensure they could be trusted.”
Keep an eye on the earth
The Microwave Limb Sounder instrument can measure natural signals from microwaves in the Earth’s atmosphere and detect them even through thick ash clouds.
“MLS was the only instrument with sufficient coverage to capture the water vapor plume as it happened and the only one unaffected by the ash the volcano was releasing,” Millán said.
The Aura satellite was launched in 2004 and since then has only measured two volcanic eruptions that have released large amounts of water vapor so high 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, which could lead to warmer surface temperatures. According to the researchers, the excess water vapor could remain in the stratosphere for several years.
The extra water vapor in the stratosphere could also lead to chemical reactions that temporarily help deplete Earth’s protective ozone.
Anatomy of an outbreak
Fortunately, the warming effect of the water vapor can be expected to be small and transient, dissipating as the additional vapor decreases. Researchers don’t think it will be enough to exacerbate existing conditions from the climate crisis.
The researchers believe that the main reason for the amount of water vapor blown up was the depth of the volcano’s caldera, 150 meters below sea level.
If it had been too deep, the depth of the ocean would have dampened the eruption, and if it had been too shallow, the amount of seawater heated by the erupting magma would not have matched the amount that would have reached the stratosphere, they said the explorers.
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