Krakatau, a volcanic island in Indonesia, killed more than 30,000 people when it erupted in 1883. One might assume that volcanic debris posed the major threat, yet many of the victims died from a tsunami caused by the volcanic eruption instead.
Volcanoes at sea can pose hazards quite different from those on land, as their impact can vary depending on how the volcanic activity interacts with seawater. In the deep ocean, high water pressure can suppress explosive volcanic activity, making eruptions less destructive. But closer to the surface, the lower water pressure and the high temperatures of volcanic material can cause violent explosions. Yet scientists still do not fully understand the conditions under which volcanic activity can cause a tsunami.
To better understand these risks, an international team of researchers examined the 2022 Hunga eruption in Tonga, focusing on the rapid caldera collapse that may have amplified its powerful tsunami. Calderas form when the ground above a magma reservoir collapses as the magma drains away. Comparisons of seafloor topography before and after the eruption showed that a roughly four-kilometer-wide caldera sank by about a kilometer during the eruption.
Source: arstechnica.com
