Small undersea volcanoes may unleash outsized tsunamis

Undersea volcanoes, such as Indonesia's Krakatoa in 1883, can trigger devastating tsunamis that cause more fatalities than the eruption itself. Researchers are seeking to better understand these risks. An international team of scientists studied the 2022 Hunga Tonga eruption in Tonga.

The study focused on the rapid collapse of the volcano's caldera, which is believed to have amplified its powerful tsunami. A caldera forms when the ground above a magma chamber collapses as the magma drains away.

Comparisons of seafloor topography before and after the eruption revealed that a caldera approximately four kilometers wide sank by about one kilometer during the event. This collapse, combined with submarine conditions, may explain the tsunami's magnitude.

Deep-sea eruptions are often suppressed by high water pressure. Nearer the surface, however, lower pressure and high temperatures of volcanic material can cause violent explosions. Scientists continue to advance understanding of the conditions under which volcanic activity can generate tsunamis.