The volcanic eruption that rocked the South Pacific kingdom of Tonga earlier this month was hundreds of times more powerful than the atomic bomb the United States dropped on Hiroshima during World War II, according to an analysis by NASA scientists.
"This is a preliminary estimate, but we think the amount of energy released by the eruption was equivalent to somewhere between 4 to 18 megatons of TNT," says Jim Garvin, chief scientist at NASA's Goddard Space Flight Center, to NASA's Earth Observatory blog.
For comparison, NASA scientists estimate the 1980 eruption of Mount St. Helens released 24 megatons of energy, per CNN's Rhea Mogul and Alex Stambaugh. Tonga’s recent event is the most powerful volcanic eruption on Earth in more than 30 years, following that of Mount Pinatubo in 1991, says University of Auckland volcanologist Shane Cronin to Kim Moodie of Radio New Zealand.
The eruption of the Hunga-Tonga-Hunga-Ha'apai volcano sent a dramatic plume of ash and water vapor 25 miles into the atmosphere and generated nearly 50-foot tsunami waves that hit parts of Tonga’s main island and sent swells across the Pacific. The blast also severed the nation’s internet cable, cutting off communication to the remote archipelago for days.
#NASAWorldview Image of the Week: Explosive Eruption of #HungaTonga - Hunga Ha'apai Volcano as observed on Jan. 15, 2022 by the ABI instrument aboard the @NOAA GOES-West satellite. Learn more: https://t.co/1qBhuelg3J GeoColor Imagery provided by NOAA/NESDIS/STAR pic.twitter.com/yRkR0bfg9U— NASAEarthdata (@NASAEarthData) January 18, 2022
To calculate the power of the event, scientists used a combination of satellite images and on-the-ground surveys, Brandon Specktor reports for Live Science. The researchers took a range of evidence into account, including the amount of rock that was removed during the explosion, and the height and size of the cloud.
The Hunga Tonga-Hunga Ha'apai volcanic island was once two landmasses, but a 2015 eruption joined the two islands. Small eruptions in late December 2021 actually added more land to the islands as well before the volcano quieted down for about a week.
Then, an eruption in the early morning hours of January 14 was so powerful that it obliterated the new land, along with large portions of the two older islands, explains volcanologist Ed Venzke of Smithsonian's Global Volcanism Program. The remaining islands form the upper tip of the underwater volcano, which rises more than a mile from the seafloor and stretches 12 miles wide. Significantly, the blast left the main eruptive vent submerged under water—perhaps only in a shallow pool, but deep enough to make the explosion on January 15 all the more powerful.
"When the pulse of magma breached the now-underwater surface, it was in immediate contact with seawater, triggering what was obviously a major steam explosion," Venzke says via email.
One reason for the size of the cloud from the blast is the interaction between hot magma and seawater, which causes violent blasts of steam. Some of these hydromagmatic eruptions that happen in shallow seas or lakes are categorized as “Surtseyan.”
"Some of my colleagues in volcanology think this type of event deserves its own designation," Garvin said in a statement. "For now, we're unofficially calling it an 'ultra Surtseyan' eruption."
Unlike the eruption of Mount Pinatubo, which ejected ash and smoke for hours, the eruption in Tonga lasted less than an hour, per NPR’s Geoff Brumfiel. Experts don’t think that the blast from Hunga Tonga-Hunga Ha'apai will cause any short-term shifts to the climate, as some other volcanic eruptions have done previously.
Since the explosion, the vast majority of Tongans have been affected by falling ash, and three people were killed in the tsunami last week. The small particulate matter blasted into the air continues to pose a health risk to Tonga’s more than 100,000 residents, as breathing smoke and ash can inflame and damage heart and lungs tissue, and irritate eyes and skin.
Because of the risk of spreading Covid-19, Tonga has requested that aid work be carried out by locals through groups like the Red Cross rather than foreign workers.