When the Hunga Tonga-Hunga Ha’apai undersea volcano erupted on Jan. 15, 40 miles (65 kilometers) north of Tonga’s capital, it created a tsunami as well as a sonic boom that rippled around the world — twice. The explosion sent a high plume of water vapor into the stratosphere, which is between 8 and 33 miles (12 and 53 kilometers) above the Earth’s surface. It was enough water to fill 58,000 Olympic-sized swimming pools, according to NASA satellite detections. The detection was made by the Microwave Limb Sounder instrument on NASA’s Aura satellite. The satellite measures water vapor, ozone and other gases in the atmosphere. After the explosion, scientists were surprised by the water vapor measurements. They estimate that the explosion 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 in the stratosphere. That’s nearly four times the amount of water vapor that reached the stratosphere after the 1991 eruption of Mount Pinatubo in the Philippines. A new study on the water vapor findings was published in July in Geophysical Research Letters. “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 inspect all measurements on the plume to make sure they were reliable.”
LET’S KEEP AN EYE ON THE EARTH
The Microwave Limb Sounder instrument can measure the natural microwave signals from the Earth’s atmosphere and detect them even through dense ash clouds. “The MLS was the only instrument with a dense enough coverage to capture the plume of water vapor as it happened, and the only one unaffected by the ash released by the volcano,” Millán said. The Aura satellite was launched in 2004 and since then has measured only two volcanic eruptions that raised significant water vapor that high into the atmosphere. But water vapor from the 2008 Kasatochi event in Alaska and the 2015 Calbuco eruption in Chile dissipated fairly quickly. Typically, powerful volcanic eruptions such as Mount Pinatubo or the 1883 Krakatoa event in Indonesia cool the Earth’s surface temperature because the gas, dust and ash they spew reflect sunlight into space. This “volcanic winter” occurred after the eruption of Mount Tambora in 1815, triggering the “year without a summer” in 1816. The Tonga eruption was different because the water vapor it sent into the atmosphere can trap heat, which could cause higher surface temperatures. The excess water vapor could remain in the stratosphere for several years, according to the researchers. Additional water vapor in the stratosphere could also lead to chemical reactions that temporarily contribute to the depletion of Earth’s protective ozone.
ANATOMY OF EXPLOSION
Fortunately, the effect of the water vapor heating is expected to be small and temporary and will dissipate as the excess vapor diminishes. Researchers do not believe it will be enough to worsen existing conditions due to the climate crisis. Researchers believe that the main reason for the amount of rising water vapor was due to the depth of the volcano’s caldera 490 feet (150 meters) below the surface of the ocean. If it were too deep, the depth of the ocean would have muted the eruption, and if it were too shallow, the amount of seawater heated by the erupting magma would not match what reached the stratosphere, the researchers said. Scientists are still working to understand the unusually energetic explosion and all its superlatives, including the hurricane-force winds that reached space.
