Phreatic eruption at the summit of Mount St. Helens, Washington. Mount St Helens is an active Stratovolcano located in Skamania County, Washington, in the Pacific Northwest region of the United States

Phreatic eruptions, also called ultravulcanian eruptions, occur when rising magma makes contact with ground or surface water. Magma (Plurals magmas and magmata) is molten rock that sometimes forms beneath the surface of the Earth (or any other Terrestrial planet Groundwater is Water located beneath the Ground surface in Soil pore spaces and in the Fractures of lithologic formations The extreme temperature of the magma (anywhere from 600 °C to 1,170 °C (1110–2140 °F)) causes near-instantaneous evaporation to steam resulting in an explosion of steam, water, ash, rock, and volcanic bombs. Uses A Steam engine uses the expansion of steam in order to drive a Piston or Turbine to perform Mechanical work. A volcanic bomb is a globe of molten rock ( Tephra) larger than 65 mm (2 At Mount St. Helens hundreds of steam explosions preceded a 1980 plinian eruption of the volcano. Mount St Helens is an active Stratovolcano located in Skamania County, Washington, in the Pacific Northwest region of the United States Plinian eruptions are Volcanic eruptions marked by their similarity to the eruption of Mt Plate tectonics and hotspots Divergent plate boundaries At the A less intense geothermal event may result in a mud volcano. In Geology, geothermal refers to heat sources within the planet Note See the Volcano article for information on Magmatic volcanoes such as Mount St In 1949, Thomas Jaggar described this kind of activity as steam-blast eruptions. Thomas A Jaggar (1871-1953 was the founder and first Director of the Hawaiian Volcano Observatory.

Phreatic eruptions typically include steam and rock fragments; the inclusion of lava is unusual. The term phreatic is used in Earth sciences to refer to matters relating to ground water below the static Water table (the word originates from the Greek The temperature of the fragments can range from cold to incandescent. Incandescence is the emission of Light (visible Electromagnetic radiation) from a hot body due to its temperature If molten material is included, the term phreato-magmatic may be used. These eruptions occasionally create broad, low-relief craters called maar. A volcanic crater is a circular depression in the ground caused by volcanic activity A maar is a broad low- Relief Volcanic crater that is caused by a Phreatomagmatic eruption, an Explosion caused by Groundwater Phreatic explosions can be accompanied by carbon dioxide or hydrogen sulfide gas emissions. Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single Hydrogen sulfide (or hydrogen sulphide) is the Chemical compound with the formula H 2 S. The former can asphyxiate at sufficient concentration; the latter is a broad spectrum poison. A 1979 phreatic eruption on the island of Java killed 149 people, most of whom were overcome by poisonous gases. Java (Jawa is an Island of Indonesia and the site of its Capital city Jakarta.

It is believed the 1883 eruption of Krakatoa - which obliterated most of the volcanic island and created the loudest sound in recorded human history - was a phreatic event. Krakatoa ( Indonesian: Krakatau) also spelled Krakatao or Krakatowa, is a volcanic island in the Sunda Strait Kilauea, in Hawaii, has a long record of phreatic explosions; a 1924 phreatic eruption hurled rocks estimated at eight tons up to a distance of one kilometer. Kīlauea (kiːlauea is an active Volcano in the Hawaiian Islands, one of five Shield volcanoes that together form the Island of Hawai{{okina}}i The State of Hawaii ( or həˈwaɪʔiː Hawaiian: Mokuāina o Hawaii) is a state in the United States located on an Archipelago in the Additional examples are the 1963–65 eruption of Surtsey, the 1965 eruption of Taal Volcano, and the 1982 Mount Tarumae erruption. Surtsey ( Icelandic: " Surtur's island" is a volcanic Island off the southern Taal Volcano is an active Volcano on the island of Luzon in the Philippines. is located in the Shikotsu-Toya National Park in Hokkaidō, Japan.

References

• USGS Photo Glossary Entry for "Phreatic Eruption"