Phreatomagmatic Eruptions - John Seach

A phreatomagmatic eruption is an explosive water-magma interaction.
Large amounts of steam and magmatic gases are emitted.

Grain deposits from phreatomagmatic explosion involving high water/ magma ratios are extremely fine grained and distinctly poorly sorted. in contrast, deposits resulting from low water/magma ratios are commonly coarse and relatively well sorted.

An example of a Phreatomagmatic Eruption was the eruptions of Mt Usu in Japan in April 2000.

Phreatomagmatic eruptions at basaltic volcanoes are capable of producing pyroclastic flows.