Products of explosive subaqueous felsic eruptions based on examples from the Hellenic Island Arc, Greece

Abstract

We review the outflow products of three explosive felsic eruptions derived from submarine vents in the Hellenic Island Arc, Greece. The facies characteristics vary due to the differences in eruption volume (>0.3-150 km 3 ), water depth (tens to hundreds of metres), depositional setting (subaerial or submarine), plume dynamics and inferred eruption intensity. Phreatoplinian eruptions are only known from vents that have been sufficiently shallow (a few tens of metres) to optimise magma/water interaction and produce subaerial plumes. Even then, phreatoplinian activity is suppressed in favour of exclusively dry activity at sufficiently high eruption rates. In contrast, explosive felsic eruptions sourced from deeper vents (>∼200 m) produce large quantities of pumice (reaching metres across) and ash, with subordinate lithic clasts in plumes that are at least dominantly submarine. Transport in water preserves the quenched margins on the pumice clasts. The eruption rate and incorporation of dense clasts influences the plume dynamics. Eruptions with significant vent erosion expel dense lithic clasts that generate submarine gravity currents. Pumice clasts that are sufficiently large to remain hot and buoyant rise through the water column until they become waterlogged and settle depositing a reversely size and density graded bed. Lower intensity eruptions with very little vent erosion, are dominated by coarse proximal pumiceous water-settled fallout that is resedimented down slope of the growing pumice cone.