Surtseyan eruption

A Surtseyan eruption is an explosive style of volcanic eruption that takes place in shallow seas or lakes when rapidly rising and fragmenting hot magma interacts explosively with water and with water-steam-tephra slurries.

Volcanoes of this type are known as 'tuff cones' and 'tuff rings' because the volcanic ash of which they are made soon solidifies by chemical reaction into a hard rock known as 'tuff'.

Surtseyan eruptions are characteristically unsteady, with phases of rapid repeated short, violent explosions separated by more quiescent phases dominated by steam generation and condensation.

The resultant deposits are characteristically well bedded with abundant evidence for moist conditions (e.g. ash aggregates, vesiculated ash layers, and soft-state deformed layers).

Much of the wet tephra repeatedly slumps back down into the volcano's crater to be re-ejected by further watery explosions.