A study found that during the massive eruption of the Hunga Tonga volcano in the South Pacific in 2022, an undersea caldera about 5 kilometers wide subsided vertically by an average of about 1 kilometer nearly simultaneously with the eruption.
Korea Polar Research Institute (KOPRI) said on the 14th that it had identified that a large-scale "piston-type collapse" occurred during the Tonga volcanic eruption process. The findings were published on the 11th (local time) in the international journal Nature Geoscience.
Korea Polar Research Institute (KOPRI) formed an emergency survey team, "K-HEART," led by principal researcher Park Sung-hyun immediately after the eruption in Jan. 2022. About 80 days after the explosion, the icebreaking research vessel Araon, which was returning from Antarctica, was deployed to the site to secure seafloor topography, seismic, ocean observation, and geomagnetic data as well as rock and ash samples. The team then jointly analyzed changes in seafloor topography and the volcano's internal structure before and after the eruption with researchers from the University of Auckland and Auckland University of Technology.
The analysis showed that a total of 8.9 cubic kilometers of material was displaced by the eruption. That is enough to fill about 600 million 25-ton dump trucks and could cover all of Seoul to a height of 15 meters. Of this, about 77%, or 6.85 cubic kilometers, was found to have resulted from the rapid subsidence of the caldera at the volcano's center.
The caldera, which had been at a depth of 150 to 200 meters before the eruption, deepened to a maximum depth of about 850 meters immediately after. The research team analyzed that such a large undersea collapse in a short time may have been one of the factors that increased the size of the tsunami.
Seismic surveys also confirmed that volcanic clastic deposits up to about 150 meters thick had accumulated inside the caldera. Beneath the sediment, the actual caldera floor was found to reach a depth of about 1,000 meters. In particular, landslide deposits were found between and below the volcanic clastic layers. The researchers view this as evidence that caldera collapse and undersea landslides occurred simultaneously during the massive eruption.
Dozens of submarine volcanoes and calderas are clustered around the Tonga waters. The researchers believe the results can be used to understand the process of submarine volcano collapse and the mechanisms of volcanic tsunamis.
Park Sung-hyun, principal researcher at Korea Polar Research Institute (KOPRI), said, "Through the emergency survey, we were able to confirm the rapid collapse process of the Tonga volcano," and added, "We plan to continue tracking changes in the growth, major eruptions, and post-collapse stages of submarine volcanoes through follow-up research."
References
Nature Geoscience (2026), DOI: https://doi.org/10.1038/s41561-026-02099-7