1 km Collapse of the Ocean Floor During Tonga Volcanic Eruption: 'Piston-Type Collapse' That Amplified the Tsunami [Reading Science]

Caldera Collapse Process Revealed by Araon Expedition
8.9 km³ of Material Displaced--Equivalent to 600 Million Dump Trucks

During the major eruption of the Hunga Tonga volcano in the South Pacific in January 2022, a submarine caldera approximately 5 kilometers wide collapsed by an average of about 1 kilometer almost simultaneously with the eruption. The volume of material displaced by the explosion alone was enough to fill around 600 million 25-ton dump trucks. Such a massive underwater collapse occurring in such a short time may have contributed to amplifying the tsunami triggered by the event.

The Korea Polar Research Institute announced on September 15, 2026, that an international research team led by principal researcher Park Soonghyun analyzed field data from the icebreaker research vessel Araon and clarified the process of a large-scale 'piston-type collapse' of the submarine caldera during the Hunga Tonga volcanic eruption. The findings were published in the international journal Nature Geoscience, with principal researcher Park serving as the corresponding author.

Seismic sparker survey data and interpretation obtained by the Araon in April 2022 from the Hunga Tonga volcano. It shows volcanic clastic deposits, landslide deposits, and internal structures accumulated inside the caldera. The landslide deposits found between and below the volcanic clastic deposits provide important evidence that the caldera collapse occurred simultaneously with the major eruption. Provided by the Korea Polar Research Institute (Image from the paper published in Nature Geoscience)

The Hunga Tonga volcano erupted violently on January 15, 2022. The eruption generated a massive volcanic ash plume and shockwaves, which triggered tsunamis across the Pacific Ocean.

The Korea Polar Research Institute quickly formed an emergency investigation team, K-HEART (Korean Hunga Eruption Araon Research Team), in the immediate aftermath of the eruption. The Araon, returning from Antarctica, was dispatched to the site about 80 days after the explosion to collect data on submarine topography, seismic signals, ocean and geomagnetic observations, as well as rock and volcanic ash samples.

Collapse of the Caldera During Eruption… 77% of Total Material Movement

A comparison of the submarine topography before and after the eruption revealed that the total amount of material relocated by the explosion reached 8.9 km³. This is equivalent to filling approximately 600 million 25-ton dump trucks or covering the entire area of Seoul with a layer about 15 meters deep.

Notably, about 6.85 km³, or roughly 77% of the total, was comprised of materials that moved as a result of the sudden collapse of the caldera at the volcano's core, not from ejecta propelled by the explosion.

The depth of the caldera, which was between 150 and 200 meters before the explosion, increased to a maximum of 850 meters immediately after the eruption. This signifies a 'piston-type collapse' in which the caldera, about 5 kilometers wide, dropped vertically by an average of about 1 kilometer almost simultaneously with the volcanic eruption.

The research team analyzed that this rapid and large-scale collapse of the underwater terrain in a short period likely displaced large volumes of seawater, significantly amplifying the tsunami that occurred at the time.

Seismic investigations also allowed the researchers to look beneath the visible seafloor. Inside the caldera, volcanic clastic deposits up to about 150 meters thick were found, and after accounting for these deposits, the true caldera floor was identified at a depth of approximately 1,000 meters. Landslide sediment layers were also discovered both between and below the volcanic clastic deposits. The research team interpreted these findings as evidence that the collapse of the caldera and underwater landslides happened concurrently during the major eruption.

This study is expected to help improve our understanding of how submarine collapses triggered by volcanic eruptions influence tsunami occurrence and magnitude. As dozens of submarine volcanoes and calderas are clustered around Tonga, the findings could also aid in refining models for predicting volcanic tsunamis and in assessing the risks posed to infrastructure such as subsea communications cables.

Principal researcher Park commented, "Despite great uncertainty, we were able to clarify the rapid collapse process thanks to the swift organization of the K-HEART team and our meticulous emergency investigations. Through follow-up research, we aim to use the Tonga volcano as a natural laboratory to trace the development, major eruptions, collapse, and subsequent changes of a submarine volcano."

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