Topic summary
Magmatic eruption
Extracted from the Wikipedia article Volcanic eruption.
Phreatomagmatic
Phreatomagmatic eruptions are eruptions that arise from interactions between water and magma. They are driven by thermal contraction of magma when it comes in contact with water (as distinguished from magmatic eruptions, which are driven by thermal expansion). This temperature difference between the two causes violent water-lava interactions that make up the eruption. The products of phreatomagmatic eruptions are believed to be more regular in shape and finergrained than the products of magmatic eruptions because of the differences in eruptive mechanisms.