Introduction: A deductive outline and topical overview of subaqueous explosive volcanism

Subaqueous eruptions are the most abundant on earth, and the proportion of such eruptions that are explosive is larger than generally appreciated though still poorly constrained. Subaqueous eruptions are fundamentally affected by water's ability to vaporize upon contact with magma, its high density (in comparison with air) and the accompanying increase in confining pressure with depth of eruption, its greater viscosity than air, and its high heat capacity and thermal conductivity. The effects are both on source dynamics of the eruptions (exit conditions, fragmentation) and the transport and deposition of eruptive products. Interpretation of ancient subaqueous deposits is important both practically, because they host significant mineral deposits, and more broadly in order to understand how volcanoes work on the ¾ of our planet beneath water. Successful interpretation requires an understanding of the full range of water's effects on eruptions in order to sail backwards from deposit characteristics through deposition and transport processes and back into the vents. Investigation of modern seafloor volcanoes demonstrates a range of volcano and eruption styles, and is also providing insight into mineralization sites and processes within still-active magmatic systems.