(Of a volcanic eruption) in which both magmatic gases and steam from groundwater are expelled.
- These are commonly present as pyroclastic deposits rather than lava because their early arrival favours interaction with groundwater to produce phreatomagmatic eruptions, and/or because they have higher volatile contents.
- Mud and sand volcanoes are positive topographic features that have many of the aspects of normal phreatomagmatic volcanism resulting from explosive interaction between hot magma and water.
- A similar degree of compositional variation between pyroclast glasses of phreatomagmatic pyroclastic rocks and intruding dykes has been recognized from the vent remnant of Szigliget, western Hungary.
Mid 20th century: from Greek phrear, phreat- 'a well' + magmatic (see magma).
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