A phreatic eruption, also called a phreatic explosion, ultravulcanian eruption or steam-blast eruption, occurs when

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natura ...

heats

ground water Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidate ...

or surface water. The extreme temperature of the magma (anywhere from ) causes near-instantaneous evaporation of water to

steam Steam is a substance containing water in the gas phase, and sometimes also an aerosol of liquid water droplets, or air. This may occur due to evaporation or due to boiling, where heat is applied until water reaches the enthalpy of vaporizatio ...

, resulting in an explosion of steam, water, ash, rock, and

volcanic bomb A volcanic bomb or lava bomb is a mass of partially molten rock (tephra) larger than 64 mm (2.5 inches) in diameter, formed when a volcano ejects viscous fragments of lava during an eruption. Because volcanic bombs cool after they l ...

s. At Mount St. Helens in Washington state, hundreds of steam explosions preceded the 1980 Plinian eruption of the

volcano A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates ...

. A less intense geothermal event may result in a

mud volcano A mud volcano or mud dome is a landform created by the eruption of mud or slurries, water and gases. Several geological processes may cause the formation of mud volcanoes. Mud volcanoes are not true igneous volcanoes as they do not produce ...

Phreatic ''Phreatic'' is a term used in hydrology to refer to aquifers, in speleology to refer to cave passages, and in volcanology to refer to a type of volcanic eruption. Hydrology The term phreatic (the word originates from the Greek , meaning "we ...

eruptions typically include steam and rock fragments; the inclusion of liquid

lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or ...

is unusual. The temperature of the fragments can range from cold to

incandescent Incandescence is the emission of electromagnetic radiation (including visible light) from a hot body as a result of its high temperature. The term derives from the Latin verb ''incandescere,'' to glow white. A common use of incandescence i ...

. If molten magma is included, volcanologists classify the event as a

phreatomagmatic eruption Phreatomagmatic eruptions are volcanic eruptions resulting from interaction between magma and water. They differ from exclusively magmatic eruptions and phreatic eruptions. Unlike phreatic eruptions, the products of phreatomagmatic eruptions cont ...

. These eruptions occasionally create broad, low-relief craters called ''

maar A maar is a broad, low-relief volcanic crater caused by a phreatomagmatic eruption (an explosion which occurs when groundwater comes into contact with hot lava or magma). A maar characteristically fills with water to form a relatively shallo ...

s''. Phreatic explosions can be accompanied by

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...

hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The under ...

gas-emissions. Carbon dioxide can

asphyxia Asphyxia or asphyxiation is a condition of deficient supply of oxygen to the body which arises from abnormal breathing. Asphyxia causes generalized hypoxia, which affects primarily the tissues and organs. There are many circumstances that can ...

te at sufficient concentration; hydrogen sulfide acts as a broad-spectrum poison. A 1979 phreatic eruption on the island of

Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's mo ...

killed 140 people, most of whom were overcome by poisonous gases.

Examples of phreatic eruptions

Cumbre Vieja The Cumbre Vieja (; meaning "Old Summit") is an active volcanic ridge on the island of La Palma in the Canary Islands, Spain. The spine of Cumbre Vieja trends in an approximate north–south direction, comprising the southern half of La Palma, ...

- 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 A fissure vent, also known as a volcanic fissure, eruption fissure or simply a fissure, is a linear volcanic vent through which lava erupts, usually without any explosive activity. The vent is often a few metres wide and may be many kilo ...

in the same location. *

Krakatoa Krakatoa (), also transcribed (), is a caldera in the Sunda Strait between the islands of Java and Sumatra in the Indonesian province of Lampung. The caldera is part of a volcanic island group ( Krakatoa archipelago) comprising four islands. T ...

–

Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Gui ...

, 1883 (see

1883 eruption of Krakatoa The 1883 eruption of Krakatoa ( id, Letusan Krakatau 1883) in the Sunda Strait occurred from 20 May until 21 October 1883, peaking in the late morning hours of 27 August when over 70% of the island of Krakatoa and its surrounding archipelago w ...

) – it is believed that the eruption, which obliterated most of the volcanic island and created the loudest sound in

recorded history Recorded history or written history describes the historical events that have been recorded in a written form or other documented communication which are subsequently evaluated by historians using the historical method. For broader world his ...

, was a phreatomagmatic event. *

Ritter Island Ritter Island is a small crescent-shaped volcanic island north-east of New Guinea, situated between Umboi Island and Sakar Island. There are several recorded eruptions of this basaltic-andesitic stratovolcano prior to a spectacular lateral coll ...

–

Papua New Guinea Papua New Guinea (abbreviated PNG; , ; tpi, Papua Niugini; ho, Papua Niu Gini), officially the Independent State of Papua New Guinea ( tpi, Independen Stet bilong Papua Niugini; ho, Independen Stet bilong Papua Niu Gini), is a country i ...

, 1888 (see

1888 Ritter Island eruption and tsunami On the morning of March 13, 1888, an explosion took place on Ritter Island, a small volcanic island in the Bismarck and Solomon Seas, between New Britain and Umboi Island. This event is the largest volcanic island sector collapse in recent his ...

) – Resulted in the largest lateral spreading of a volcanic cone in human history. * Kilauea –

Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only stat ...

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...

– 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."On May 10, 1924, a violent phreatic (steam) eruption began in Halema'uma'u that sent repeated columns of ash high into the sky. The explosions continued for 18 days, with the largest occurring on May 18. The steam explosions hurled rocks as large as eight tons as far as 0.6 miles from the crater; these blocks still surround Halema'uma'u. One of these blocks fatally injured a Mr. Taylor, who approached too close to the crater to take a photograph.
Phreatic Eruptions
Hawaiian Volcano Observatory,

US Geological Survey The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, and ...

, 6 May 1994. *

Surtsey Surtsey (" Surtr's island" in Icelandic, ) is a volcanic island located in the Vestmannaeyjar archipelago off the southern coast of Iceland. At Surtsey is the southernmost point of Iceland. It was formed in a volcanic eruption which began ...

–

Iceland Iceland ( is, Ísland; ) is a Nordic island country in the North Atlantic Ocean and in the Arctic Ocean. Iceland is the most sparsely populated country in Europe. Iceland's capital and largest city is Reykjavík, which (along with its ...

, 1963–65 * Taal Volcano –

Philippines The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no), * bik, Republika kan Filipinas * ceb, Republika sa Pilipinas * cbk, República de Filipinas * hil, Republ ...

, 1965, 1977,

2020 2020 was heavily defined by the COVID-19 pandemic, which led to global social and economic disruption, mass cancellations and postponements of events, worldwide lockdowns and the largest economic recession since the Great Depression in t ...

* Mount Ontake – Japan, 2014 (see

2014 Mount Ontake eruption A volcanic eruption of took place on September 27, 2014, killing 63 people. Mount Ontake is a volcano located on the Japanese island of Honshu around 100 kilometres (62 mi) northeast of Nagoya and around 200 km (120 mi) west of T ...

) *

Mayon Volcano Mayon ( bcl, Bulkan Mayon; tl, Bulkang Mayon, ), also known as Mount Mayon and Mayon Volcano ( es, Monte Mayón, Volcán Mayón), is an active stratovolcano in the province of Albay in Bicol, Philippines. A popular tourist spot, it is renow ...

– Philippines, 2013 *

Whakaari/White Island Whakaari / White Island (, mi, Te Puia Whakaari, lit. "the dramatic volcano"), also known as White Island or Whakaari, is an active andesite stratovolcano situated from the east coast of the North Island of New Zealand, in the Bay of Plent ...

–

New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island coun ...

, 2019 (see

2019 Whakaari/White Island eruption On 9 December 2019 Whakaari / White Island, an active stratovolcano island in New Zealand's northeastern Bay of Plenty region explosively erupted. The island was a popular tourist destination, known for its volcanic activity, and 47 people wer ...

) * Mount Bulusan – Philippines, 2022

References

{{Types of volcanic eruptions Volcanic eruption types

Examples of phreatic eruptions

See also

References