Hydrovolcanic activity on a continental shelf inferred from the subsurface diatreme- and crater-filling deposits of Jeju Island, Korea

Abstract Jeju Island comprises numerous tuff rings and cones their reworked deposits in the subsurface, which formed on ca. 120-m-deep Yellow Sea continental shelf under fluctuating Quaternary sea levels. Tens of meter-thick massive were found by chance during groundwater drilling at three sites. These are interpreted as either syn-eruptive diatreme-filling or post-eruptive crater-filling deposits, both hydromagmatic volcanoes. The diatremes cut into sediment, 70 to 250 m thick, developed generally within it below Abundant external water was therefore available for explosive magma-water interactions shallow diatreme deposit one core shows some features attributable extreme wetness saturation fill, such matrix support larger clasts, meager vertical changes content, an absence related particle adhesion. Fluidally shaped clasts with delicate reentrant margins suggest minimal abrasion breakage a water-saturated highly fluid slurry tephra that probably filling bowl-like diatreme, is distinguished from phreatomagmatic kimberlite diatremes. other cores comprise blocky angular sideromelane ash matrix, suggesting explosions deeper level. One contains collapsed thinly stratified emplaced pyroclastic surges, indicating associated emergent ring. Both Surtseyan eruptions have occurred controls subsurface there can be variety different sizes, shapes, material characteristics beneath craters volcanoes, including not only maars but also cones.