Phreatic eruption

A phreatic eruption, also called a phreatic explosion, ultravulcanian eruption or steam-blast eruption,^[1] occurs when magma heats ground water or surface water. The extreme temperature of the magma (anywhere from 500 to 1,170 °C (930 to 2,100 °F)) causes near-instantaneous evaporation of water to steam, resulting in an explosion of steam, water, ash, rock, and volcanic bombs.^[2] At Mount St. Helens in Washington state, hundreds of steam explosions preceded the 1980 Plinian eruption of the volcano.^[2] A less intense geothermal event may result in a mud volcano.^{[citation needed]}

A scheme of a phreatic eruption: 1: water-vapor cloud, 2: magma conduit, 3: layers of lava and ash, 4: stratum, 5: water table, 6: explosion, 7: magma chamber

Phreatic eruption at the summit of Mount St. Helens, Washington, in the spring of 1980

Phreatic eruptions typically include steam and rock fragments; the inclusion of liquid lava is unusual. The temperature of the fragments can range from cold to incandescent. If molten magma is included, volcanologists classify the event as a phreatomagmatic eruption. These eruptions occasionally create broad, low-relief craters called maars. Phreatic explosions can be accompanied by carbon dioxide or hydrogen sulfide gas-emissions. Carbon dioxide can asphyxiate at sufficient concentration; hydrogen sulfide acts as a broad-spectrum poison. A 1979 phreatic eruption on the island of Java killed 140 people, most of whom were overcome by poisonous gases.^[3]

Examples of phreatic eruptions

• Cumbre Vieja - In the 2021 La Palma eruption, new eruptive vents tended to announce themselves with a phreatic explosion, followed soon after by the opening of a new fissure vent in the same location.^{[citation needed]}
• Krakatoa – Indonesia, 1883 (see 1883 eruption of Krakatoa) – it is believed that the eruption, which obliterated most of the volcanic island and created the loudest sound in recorded history, was a phreatomagmatic event.^[4][5]
• Ritter Island – Papua New Guinea, 1888 (see 1888 Ritter Island eruption and tsunami) – Resulted in the largest lateral spreading of a volcanic cone in human history.^[6]
• Kilauea – Hawaii, United States – the volcano has a long record of phreatic explosions; a 1924 phreatic eruption hurled rocks estimated at eight tons up to a distance of one kilometer.^[7]
• Surtsey – Iceland, 1963–65
• Taal Volcano – Philippines, 1965, 1977, 2020
• Mount Ontake – Japan, 2014 (see 2014 Mount Ontake eruption)
• Mayon Volcano – Philippines, 2013
• Whakaari/White Island – New Zealand, 2019 (see 2019 Whakaari/White Island eruption)
• Mount Bulusan – Philippines, 2022

See also

• Types of volcanic eruptions
• Phreatic – Term used in several scientific disciplines
• Hydrothermal explosion – Explosion of superheated ground water converting to steam
• Steam cannon – Projectile launcher powered by heat and water