Small undersea volcanoes may unleash outsized tsunamis

This research suggests that tsunami risk assessments may need to consider the speed of caldera collapse in submarine volcanoes, not just eruption size.

A recent study analyzing the 2022 Hunga eruption in Tonga suggests that rapid caldera collapse, rather than just the volcanic explosion itself, may significantly amplify tsunami generation. Researchers compared pre- and post-eruption seafloor topography, revealing that the Hunga caldera, a relatively small feature approximately four kilometers wide, collapsed by nearly a kilometer. This rapid, piston-style subsidence of the seafloor displaced a massive volume of water. The study proposes that the thin roof of Hunga's magma reservoir contributed to this swift collapse, even with a moderate loss of magma. The findings indicate that even smaller underwater volcanoes with similar geological characteristics could pose significant tsunami risks, highlighting the need for better understanding and monitoring of submarine volcanic activity.

The Hunga eruption's caldera collapse, characterized by a deep, piston-like subsidence, displaced an estimated 6.85 cubic kilometers of water. This rapid displacement, occurring even as the volcano erupted, contrasts with expectations that only large-scale volcanic explosions generate major tsunamis. The study's focus on the caldera's geometry, particularly its thin, broad magma reservoir roof, provides a mechanism for such swift collapse, implying that other volcanoes with similar structures could pose a comparable, underestimated threat. This shifts the focus from eruption magnitude alone to the specific geological dynamics of the volcanic edifice.

The implications extend to hazard mitigation and infrastructure planning, especially in volcanically active regions like the Tonga-Kermadec arc. The research underscores an urgent need for high-resolution seafloor mapping of underwater calderas, which are often poorly surveyed. Such detailed data is crucial for enhancing tsunami early-warning systems and protecting critical underwater infrastructure. Without this information, regions with numerous submarine volcanoes remain vulnerable to unexpected and potentially devastating tsunami events originating from rapid caldera subsidence.