Pyroclastic density currents explain far-reaching and diverse seafloor impacts of the 2022 Hunga Tonga Hunga Ha’apai eruption

Abstract The impacts of large terrestrial volcanic eruptions are apparent from satellite monitoring and direct observations1,2. However, more than three quarters of all volcanoes worldwide lie submerged beneath the ocean and the risks they pose to people and infrastructure remain poorly understood due to inaccessibility and a lack of detailed observations before and after eruptions3. Here, comparing data acquired in 2015-20174,5 and three months after the January 2022 eruption of Hunga Tonga Hunga Ha’apai, we document the wide-reaching and diverse impacts of the largest seaborne volcanic eruption in nearly 150 years6. Almost 10 km3 of seafloor material was removed during the eruption, most of which was redeposited within 20 km of the caldera by long run-out pyroclastic currents. These powerful currents damaged seafloor cables over a length of >100 km, reshaped the seafloor, and caused mass-mortality of seafloor life. Biological seafloor communities that survived the eruption were only observed where local topography provided a physical barrier to pyroclastic currents (e.g., on nearby seamounts). While the longer-term consequences of such a large eruption for human, ecological and climatic systems are emerging, we expect that these previously-undocumented refugia will play a key role in longer-term ecosystem recovery7–9.