Study reveals seafloor collapse amplified 2022 Tonga tsunami devastation

On January 15, 2022, the seafloor beneath Tonga did something geologists are still working to fully understand. A volcano called Hunga Tonga-Hunga Haʻapai erupted with such force that it sent a column of ash and gas more than 55 kilometers into the atmosphere. But the eruption itself was only part of what made the tsunami so devastating. A new study published in Nature Geoscience reveals that at nearly the same moment the volcano exploded, the seafloor beneath it collapsed—a sudden, violent drop that scientists say amplified the waves that would eventually strike coastlines across the Pacific.

The collapse was staggering in scale. The caldera, a crater roughly five kilometers wide, plunged from about 150 meters below the surface to around 850 meters down. That is a drop of roughly 700 meters in minutes. The movement displaced 8.9 cubic kilometers of seafloor material—about 6.85 cubic kilometers of that came from the caldera itself. To put that volume in perspective, it would take hundreds of millions of large dump trucks to move an equivalent amount of earth. The Korea Polar Research Institute led the international team that made this discovery, working alongside researchers from New Zealand and other institutions. They compared detailed seafloor maps made before the eruption with surveys conducted just months afterward, using the research vessel Araon to collect high-resolution data from the underwater volcano.

What matters most about this collapse is not just its size but its speed. When a section of seafloor suddenly drops that far, it creates a vacuum of sorts—the water above it gets pulled down and then pushed outward in waves. Scientists say this rapid piston-like movement of the caldera added significantly to the tsunami that the eruption itself generated. The study also found evidence that landslides were occurring simultaneously with the caldera collapse, meaning the eruption was not a single violent event but rather a series of violent changes happening together beneath the ocean. This combination of forces—the eruption, the collapse, the landslides—created the conditions for the powerful waves that reached Tonga and other Pacific islands.

The 2022 eruption left a mark on the region that is still being measured. The tsunamis damaged more than 190 kilometers of undersea telecommunications cables. The atmospheric pressure wave from the explosion was felt across the Pacific. But for the people who lived through it, the damage was more intimate and more lasting. Lusiana Kikau was working at Fafa Island Resort when the tsunami struck. Her memory of that day centers on one thing: getting her young daughter to safety. "So, we were just trying to save our daughter, so we tried to clear with two other Fijian staff, we were together on that island, just tried to save our daughter," she said in an interview. Four years later, the experience still shapes how she moves through the world. Loud sounds startle her. Thunder or any sudden noise brings her back to that day, to the sound like thunder that came before the waves.

The findings from this study matter beyond Tonga because submarine volcanoes remain poorly understood and their tsunami risks are difficult to predict. Most underwater volcanoes are hard to study—they sit beneath hundreds or thousands of meters of water, and opportunities to map them before and after major events are rare. This study suggests that even a relatively small submarine caldera can produce a much larger tsunami if its collapse happens rapidly enough. For Pacific communities living near some of the world's most active volcanic and seismic zones, that is critical knowledge. In November 2025, Tonga's Geological Services visited Hunga Tonga-Hunga Haʻapai along with researchers from other institutions, conducting the first ground-based observations since the eruption. Tonga's Ministry of Lands, Survey, Planning and Natural Resources said it would continue daily monitoring of nearby Home Reef using satellite observations of heat flow, sulfur dioxide emissions, and radar imagery. The high-precision 3-D model being constructed from the mission data will improve forecasts of future volcanic activity. For now, the science offers Pacific communities a clearer picture of how hazards can unfold beneath the ocean, often with little warning.