Small undersea volcanoes may unleash outsized tsunamis

The 1883 eruption of Krakatau in Indonesia resulted in over 30,000 deaths, primarily from a tsunami triggered by the volcanic activity. Volcanic eruptions beneath the sea can present dangers distinct from those on land, as their effects depend on the interaction between the volcanic event and the ocean. In the deep ocean, high water pressure tends to dampen explosive volcanic eruptions, thereby reducing destructive potential.

However, as eruptions approach shallower depths, the reduced water pressure and higher temperatures of the volcanic materials can lead to more violent explosions. Despite this, the specific conditions that trigger tsunamis due to volcanic activity remain poorly understood. To shed light on these risks, an international team of researchers studied the 2022 Hunga eruption in Tonga, with a focus on the rapid caldera collapse that may have intensified its devastating tsunami.

Calderas are created when the land above a magma chamber sinks as the magma beneath drains away. By comparing seafloor topography before and after the eruption, the researchers found that a caldera approximately 4 kilometers in diameter dropped by around a kilometer during the eruption.