Source mechanism of impulsive seafloor events that track submarine lava flows.

Most of Earth's volcanic eruptions are hidden beneath the ocean in complete darkness. Recent studies suggested that a type of impulsive event can track submarine lava flows, but their source mechanism remains uncertain. We analyze >20,000 impulsive events from the 2015 Axial Seamount eruption and find that their seismo-acoustic waveform characteristics suggest an implosive source mechanism. Integrating constraints from their spatiotemporal evolution with heat transfer estimates and geological observations, we propose that while the largest events might be related to volatiles degassed from magma, most events are generated by the implosion of bubbles formed from the vaporization of entrapped seawater by hot erupted lava. Similar events have been detected at other seamounts and slow to fast-spreading mid-ocean ridges, although eruptions at >3000-meter depth have proportionately fewer events because seawater vaporization is inhibited. Therefore, these impulsive seafloor events can be leveraged to remotely characterize eruption dynamics in most submarine volcanic settings.