Samuel S Pegler , David Ferguson

Deep-marine volcanism drives Earth’s most energetic transfers of heat and mass between the crust and the oceans. Seafloor magmatic activity has been correlated in time with the appearance of massive enigmatic plumes of hydrothermal fluid, known as megaplumes, yet little is known of the primary source and intensity of the hydrothermal energy release that occurs during seafloor volcanic events. Consequently the origin of megaplumes remains ambiguous. By developing a model for the dispersal of submarine tephras, we show that the transport of pyroclasts requires an extremely rapid energy discharge, forming a hydrothermal plume with characteristics matching those of megaplumes. Our results show that megaplume formation, which we predict can occur in a matter of hours, is concurrent with lava extrusion. However, the predicted release rate of heat energy considerably exceeds that available from lava alone, giving evidence that syn-eruptive discharges of heated crustal fluids provide the dominant source of megaplume energy. The ubiquity of submarine tephra deposits suggests that powerful (∼1 TW) intervals of hydrothermal dis-charge must be commonplace during eruptions in the deep-ocean.