Seafloor Surveys Reveal Massive Caldera Collapse

An international research team, including researchers from the NOC, has published new findings in Nature Geoscience detailing the profound geological impact and rapid submarine caldera collapse caused by the 2022 Hunga volcano eruption.

Using high-resolution bathymetric surveys and water column observations, scientists quantified structural changes to the ocean floor, calculating that the eruption displaced 8.9 cubic kilometres of volcanic material—equivalent to the volume of 1,500 Great Pyramids or 89,000 modern aircraft carriers. The event caused the Hunga caldera to deepen dramatically from 150 metres to 850 metres below sea level. Most of this volume was displaced by the structural collapse of the caldera itself, with remaining changes caused by surface erosion from eruption-fed currents. Despite the massive displacement, the material comprised less than 30 percent of the underlying magma reservoir.

The 2022 eruption, recognized as the most explosive volcanic event of the last century, triggered global atmospheric pressure waves, deadly tsunamis, and fast, destructive underwater flows that caused extensive damage to subsea telecommunications cables. Submerged and volcanic-island calderas of this type are linked to Earth’s largest eruptions, including the 1883 eruption of Krakatau in Indonesia. Due to the steepness and speed of the caldera collapse, Hunga produced an even larger tsunami than Krakatau, generating waves approximately 40 metres high at distances up to 100 kilometres away, though local loss of life was fortunately limited.

“Hunga gave us an extraordinary opportunity to see just how dramatically the seafloor can change during a major volcanic eruption. It is rare to have detailed maps of the seafloor from before a hazardous event. The unique datasets used in this study allow us to reconstruct what happened during the most explosive volcanic eruption this century, helping us better understand how these processes generate devastating marine hazards, like tsunamis,” said Dr Isobel Yeo, a senior volcanologist at the National Oceanography Centre (NOC) and co-author of the study.

“Most submarine volcanoes are still very poorly mapped and monitored. Building repeat observations of these volcanoes is vital if we are to better understand the hazards they pose to coastal communities and critical seafloor infrastructure,” Dr Yeo added.

Dr Marta Ribó, lead author of the study from Auckland University of Technology (AUT), highlighted the broader vulnerability of uncharted underwater regions, “There are at least 74 submarine volcanoes along the Tonga–Kermadec Arc, with 20 caldera complexes. Yet, despite the hazards they pose, they are not well-understood as they remain unexplored.”

“Seafloor mapping before and after submarine volcanoes eruptions is very rare. Despite their recognised threat, most submarine caldera volcanoes remain unmapped. The bathymetric time-series of Hunga, before and after the 2022 eruption allowed us to better understand processes governing submarine caldera formation, caldera collapse dynamics and associated hazards such as tsunamis or dense underwater flows,” Dr Ribó noted.

The event exposed a critical gap in global preparedness for submarine volcanic hazards. “Our findings underscore the urgent need for high-resolution repeat seafloor mapping to capture the dynamics of submarine caldera formation and collapse. These time-series datasets are essential for improving submarine volcano hazard monitoring, strengthening tsunami early-warning systems and protecting critical seafloor infrastructure, particularly in poorly surveyed regions such as the southwest Pacific,” said Dr Ribó.

The published study represents a collaborative effort among 22 researchers across institutions in Tonga, New Zealand, the Republic of Korea, the USA, and the UK. Rapid response investigation for NOC co-authors Isobel Yeo and Mike Clare was supported by funding from NERC under grant NE/X00239X/1.