Explosive Submarine Eruptions: The Role of Condensable Gas Jets in Underwater Eruptions

In explosive submarine eruptions, volcanic jets transport fragmented tephra and exsolved gases from the conduit into the water column. Upon eruption the volcanic jet mixes with seawater and rapidly cools. This mixing and associated heat transfer ultimately determines whether steam present in the jet will completely condense or rise to breach the sea surface and become a subaerial hazard. We develop a multiphase model with subgrid calculations for in situ steam condensation to explore the relationship between eruption conditions (e.g., water depth, mass eruption rate, and eruption temperature) and the produced steam jet height and breach potential. We find that mass eruption rate is the predominant control of jet height, more so than vent width. We present a series of parameter maps predicting the limits of eruption breach for water depths of 200, 500, and 1,000 m. We demonstrate the relationship between subsurface jets and sea surface temperature anomalies, and sea surface displacement. Lastly, we evaluate the role of dispersed ash on volcanic jet development by comparing jets with particles of different size and density, as well as differing eruption conditions with particles. Plain Language Summary In explosive underwater volcanic eruptions, gas jets carry volcanic ash and rocks into the ocean water column and potentially the atmosphere. During the eruption, the jet mixes with seawater which cools the jet and can cause steam present in the jet to condense to liquid water. This condensation controls whether the eruption jet will make it to the surface and become a hazard for nearby populations, ships, and airplanes, or will it condense completely below the surface. We present results from computer models we have developed that demonstrate the conditions necessary for an eruption to make it to the sea surface. We also show other effects the eruptive jet can have that can be measured at the surface, such as increasing the sea surface temperature or generating large waves. Lastly, we examine how including ash and rock in the gas jet can change the height of the gas jet. Key Points 2D multiphase models evaluate gas jet thrust in subaqueous explosive eruptions from vents at 200, 500, and 1,000 m water depths Mass eruption rate and water depth are the primary controls of jet height, eruption temperature and vent diameter are lesser so Surface breaching eruptions are possible from vents at 500 m water depth, but not 1,000 m depth