Understanding of submarine volcanism still lags behind understanding of subaerial volcanism for the obvious reason that eruptions are usually not, or only partially visible, and deposits are largely inaccessible. In addition, our understanding of the effects of the ambient water mass and the way in which erupting magma and water interact, and the ways in which the physical properties of the water mass control and influence eruption styles, dispersal processes and deposit characteristics, is still at a relatively early stage. In particular, in the past there has been a very simplistic approach to assessing constraints on eruption styles using only ambient hydrostatic pressure, whereas equally important properties such as bulk modulus, compressibility, deformability, attenuation properties, thermal conductivity, heat capacity, have not been adequately considered. This review summarises our understanding on these issues, and briefly summarises varying eruption conditions, styles and deposit characteristics.
The origin of pumice deposits preserved in subaqueous settings needs to be interpreted with care. They could represent local explosive events, but could also represent pumice sourced from distant explosive events and vents, even subaerial, and deposited by fallout through water, the passage of pyroclastic flows into water from subaerial vents, long distance rafting of buoyant pumice by currents, reworking and resedimentation, and even non-explosive subaqueous vesiculation and quench fragmentation of subaqueously erupted lavas in shallow or even deep water.
The Miocene Cabo de Gata volcanic succession of southeastern Spain was deposited in shallow marine environments based on inter-bedded fossiliferous limestones, which represent periods of volcanic hiatus. The volcanic facies are consistent with a shallow marine setting, involving eruption of low volatile bearing magmas to form andesite and dacite lava flows, domes and associated hyaloclastites, as well as eruptions of volatile rich rhyolitic magmas that produced pumice deposits erupted from subaerial vents or vents at water depths that were too shallow to suppress explosive eruptions through the effects of hydrostatic pressure, but were then reworked and resedimented.