Researchers Link Tonga Eruption's Tsunami to Rapid Caldera Collapse

The hazard is well documented. Krakatau, a volcanic island in Indonesia, killed more than 30,000 people when it erupted in 1883, and many of those victims died in the tsunami caused by the eruption rather than from volcanic debris.

Volcanoes at sea pose hazards quite different from those on land, because their impact can vary depending on how volcanic activity interacts with seawater. In the deep ocean, high water pressure can suppress explosive volcanic activity, making eruptions less destructive. Closer to the surface, lower water pressure and the high temperatures of volcanic material can cause violent explosions.

Scientists still do not fully understand the conditions under which volcanic activity can cause a tsunami. To better understand those risks, the researchers turned to Hunga, examining the rapid caldera collapse that may have amplified the tsunami the 2022 eruption produced.

Calderas form when the ground above a magma reservoir collapses as the magma drains away. Comparisons of seafloor topography before and after the Hunga eruption showed that a caldera roughly four kilometers wide sank by about a kilometer during the eruption. That measured subsidence is the basis for the team's focus on collapse as a mechanism capable of amplifying the tsunami generated by an eruption at sea.

The report does not resolve the broader question of forecasting when an undersea eruption will produce a tsunami. It points instead to the rapid drainage of magma and the resulting collapse of the seafloor as a process that warrants closer study, given how differently the same volcanic activity can play out in deep water and near the surface.