Imperial College Rock Library

Glossary: Surtseyan Eruption

Synonyms: surtseyan activity
    Surtseyan eruptions are explosive activity occurring due to the eruption of magma into shallow water. They are phreatomagmatic eruptions associated with a high degree of fragmentation of magma leading to large volumes of ash and lapilli, and the generation of ash and scoria cones, tuff rings and maars. They are often related to basaltic magmas although andesitic eruptions are known.
Interaction between magma and relatively shallow water in Surtseyan eruptions leads to rapid vaporisation and rapid expansion of a steam envelope. Pressure increase caused by expansion, and the collapse of the steam envelope, leads to significant fragmentation of the magma body and explosive behaviour. A defining feature of Surtseyan eruptions are the generation of base surges - high velocity, outwards moving dispersions of gas and rock particles. Base surges form by the collapse of the eruption column and trapping and pressurisation of atmospheric gas.
Typical products of Surtseyan eruptions are basaltic ash and lapilli. Fragmentation and quenching of magma leads to breccias and tuff breccias consisting of glassy juvenile clasts known as hyaloclastite breccias. Glassy materials produced by Surtseyan activity are usually intensely altered to palagonite. Lapilli with concentric layering, known as accretionary lapilli, are common and form to accretion of dust to solid particles under water-saturated conditions. Base surges have low particle densities and produced layered deposits of ash and lapilli often with structures such as cross-lamination and dune-forms indicating deposition in a current.
Surtseyan eruptions can be sub-aqueous, due to interation with seawater, lakes or glacier, or sub-aerial, due to interaction with significant quantities of ground water.

Related Terms

andesite, basalt, hyaloclastite breccia, lapilli, phreatomagmatic eruption, pyroclastic rock, volcanic eruption

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