A phreatic eruption is an explosive eruption of steam, water, mud, and other material, caused by the superheating of groundwater in contact with hot rocks. Although the rocks may be heated by magma or lava, there is no expulsion of molten rock.
The eruption of Taal Volcano in the Philippines in 1965 typifies "phreatic" (or steam-blast) behavior. Here, a great column of steam, dust, ash, and cinders is blasted to a height of several thousand feet. This type of violent eruption is believed to occur when a large quantity of ground or surface water comes in contact with hot rock or magma in a volcanic vent and is instantly and explosively flashed to steam.
- Miller, 1989
- Brantley, 1994
- Foxworthy and Hill, 1982