The seafloor record of explosive submarine volcanic eruptions

Underwater density currents triggered by marine volcanic eruptions threaten island communities and infrastructure, while their deposits provide potential archives of past major eruptions. Despite their significance, a scarcity of real-time observations and sampling of resultant deposits limits our understanding of the behaviour of such currents and the extent to which they vary in relation to triggering mechanism(s). Based on data acquired following the cataclysmic 2022 eruption of Hunga Volcano, we show that syn-eruptive vertical delivery of pyroclastic material into the ocean via low-column collapses and fountaining triggered the multidirectional dispersal of highly-concentrated underwater density currents. Rapid supply of huge volumes (<6.5 km3 18 ) of dense pyroclastic material onto the steep flanks over minutes-to-hours generated currents capable of maintaining high density and velocity 10s to 100s of kilometres from the volcano. This behaviour contrasts with density currents triggered by volcanic flank collapses and the ocean-entry of terrestrial pyroclastic density currents. We outline diagnostic criteria to identify and differentiate deposits of such underwater currents from other processes - enabling better reconstruction of the records of volcanic activity in marine sediments and enhancing hazard assessments in many submerged volcanic settings worldwide.