Phreatic eruptions are caused by the interaction of magma with water, either in the form of groundwater or surface water. The primary causes of phreatic eruptions can be summarized as follows:
- Magma intrusion: When magma intrudes into fluvial sediments, lava, or pyroclastic flows, it can interact with surface water, leading to a phreatic eruption[1].
- Hydrothermal processes: Phreatic eruptions result from rapid heating and vaporization of fluids situated at shallow levels beneath a volcano[2]. These fluids can originate from the downward percolation of meteoric fluids or the upward migration of volcanic fluids, including gases, supercritical fluids, and melts[1].
- Magmatic degassing: Phreatomagmatic eruptions, a type of phreatic eruption, are driven by magmatic processes and involve the vaporization of exogenous water as a contributing force[1].
- Pressure build-up: Phreatic explosions can occur when volatile and heat release from shallow-seated magma into the hydrothermal system, leading to a pressure build-up[3].
Phreatic eruptions can often precede, accompany, or follow a more traditional volcanic eruption[4]. They can be lethal to people close by and can cause significant damage due to the explosive expansion of steam and gas[5]. Refer to the following diagrams of two types of phreatic eruptions[6].
