A phreatic eruption is a steam-based volcanic reaction caused by the heating of water by magma. The pressure caused by underground steam forces it to escape through volcanic eruption.
The water sources of phreatic eruptions include both underground and surface water. The volcanic explosion is caused by the extremely rapid vaporization of water into steam, which occurs when underground magma is in the close vicinity of the water source. These temperatures can reach up to 1,700 degrees Celsius.
Phreatic explosions typically cause the dispersal of rock and water material. While it is common for many types of eruptions to cause the dispersal of magma, it is unusual in phreatic eruptions. Phreatic eruptions that disperse magma are known as phreatomagmatic eruptions.