Phreatic eruptions are volcanic eruptions in which magmatic processes are not the principal driving mechanism. It encompasses steam-driven explosions generated by magma intruding fluvial sediments & aquifers, lava or pyroclastic flows interacting with surfaces water, geyser-like explosions driven by depressurization of near boiling-point subterranean geothermal water, & volcanic eruptions expelling hydrothermal systems formed during periods of repose. They can be lethal to people close by, & they commonly precede large magmatic eruptions.
Mechanism of Phreatic Eruptions
Phreatic eruptions result from the rapid heating & vaporization of fluids which are commonly situated at shallow levels beneath a volcano.
- By definition, there is no solid juvenile material in the eruption products (although sometimes this can be difficult to determine).