Hydrothermal explosions occur when superheated water trapped below the surface of the Earth rapidly converts from liquid to steam, violently disrupting the confining rock. Boiling water, steam, mud, and rock fragments are ejected over an area of a few meters up to several kilometers in diameter. Although the energy originally comes from a deep

igneous Igneous rock ( ), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rocks are formed through the cooling and solidification of magma or lava. The magma can be derived from partial ...

source, this energy is transferred to the surface by circulating

meteoric water Meteoric water, derived from precipitation such as snow and rain, includes water from lakes, rivers, and ice melts, all of which indirectly originate from precipitation. The journey of meteoric water from the atmosphere to the Earth's surface is a ...

or mixtures of meteoric and magmatic water rather than by

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma (sometimes colloquially but incorrectly referred to as ''lava'') is found beneath the surface of the Earth, and evidence of magmatism has also ...

, as occurs in

volcanic eruptions A volcanic eruption occurs when material is expelled from a volcanic vent or fissure. Several types of volcanic eruptions have been distinguished by volcanologists. These are often named after famous volcanoes where that type of behavior h ...

. The energy is stored as heat in hot water and rock within a few hundred feet of the surface. Hydrothermal explosions are caused by the same instability and chain reaction mechanism as

geysers A geyser (, ) is a spring with an intermittent water discharge ejected turbulently and accompanied by steam. The formation of geysers is fairly rare and is caused by particular hydrogeological conditions that exist only in a few places on Ea ...

but are so violent that rocks and mud are expelled along with water and steam.

Cause

Hydrothermal explosions occur where shallow interconnected reservoirs of water at temperatures as high as 250 °C underlie thermal fields. Water usually boils at 100 °C, but under pressure its

boiling point The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor. The boiling point of a liquid varies depending upon the surrounding envi ...

increases, causing the water to become superheated. A sudden reduction in pressure causes a rapid

phase transition In physics, chemistry, and other related fields like biology, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic Sta ...

from liquid to steam, resulting in an explosion of water and rock debris. During the last Ice Age, many hydrothermal explosions were triggered by the release of pressure as

glacier A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...

s receded. Other causes are

seismic activity An earthquakealso called a quake, tremor, or tembloris the shaking of the Earth's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves. Earthquakes can range in intensity, from those so weak they ...

erosion Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust and then sediment transport, tran ...

, or

hydraulic fracturing Fracking (also known as hydraulic fracturing, fracing, hydrofracturing, or hydrofracking) is a well stimulation technique involving the fracturing of Formation (geology), formations in bedrock by a pressurized liquid. The process involves the ...

Yellowstone

Yellowstone National Park Yellowstone National Park is a List of national parks of the United States, national park of the United States located in the northwest corner of Wyoming, with small portions extending into Montana and Idaho. It was established by the 42nd U ...

is a thermally active area with an extensive system of hot springs,

fumarole A fumarole (or fumerole) is a vent in the surface of the Earth or another rocky planet from which hot volcanic gases and vapors are emitted, without any accompanying liquids or solids. Fumaroles are characteristic of the late stages of volcani ...

, and

mudpot A mudpot, or mud pool, is a type of acidic hot spring, or fumarole, with limited water. It usually takes the form of a pool of bubbling mud, as a result of the acid and microorganisms decomposing surrounding rock into clay and mud. Description ...

s. There are also several hydrothermal explosion craters, which are not to be confused with

caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcanic eruption. An eruption that ejects large volumes of magma over a short period of time can cause significant detriment to the str ...

s, which are collapse features. Eight of these hydrothermal explosion craters are in hydrothermally cemented glacial deposits, and two are in

Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...

ash-flow

tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock co ...

. Each is surrounded by a rim composed of debris derived from the crater, 30 to 100 feet high. More than 20 large hydrothermal explosions have occurred at Yellowstone, approximately one every 700 years. The temperature of the magma reservoir below Yellowstone is believed to exceed 800 °C causing the heating of rocks in the region. If so, the average heat flow supplied by

convection currents Convection is single or multiphase fluid flow that occurs spontaneously through the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convect ...

is 30 times greater than anywhere in the

Rocky Mountains The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in great-circle distance, straight-line distance from the northernmost part of Western Can ...

Snowmelt In hydrology, snowmelt is surface runoff produced from melting snow. It can also be used to describe the period or season during which such runoff is produced. Water produced by snowmelt is an important part of the annual water cycle in many part ...

and rainfall seep into the ground at a rapid rate and can conduct enough heat to raise the temperature of ground water to almost boiling. The phenomena of geyser basins are the product of hot ground water rising close to the surface and occasionally bubbling through. Water temperatures of 238 °C at 332 meters have been recorded at Norris Geyser Basin. Pocket Basin was originally an ice-dammed lake over a hydrothermal system. Melting ice during the last glacial period caused the lake to rapidly drain, causing a sudden change in pressure triggering a massive hydrothermal explosion.

Geysers

A hydrothermal explosion is similar to a geyser's eruption except that it includes surrounding rock and mud and does not occur periodically. One well-known hydrothermal geyser is

Old Faithful Old Faithful is a cone geyser in Yellowstone National Park in Wyoming, United States. It was named in 1870 during the Washburn–Langford–Doane Expedition and was the first geyser in the park to be named. It is a highly predictable geotherma ...

which throws up plumes of steam and water approximately every hour and a half on average. Rarely has any steam explosion violently hurled water and rock thousands of feet above the ground; however in

Yellowstone Yellowstone National Park is a List of national parks of the United States, national park of the United States located in the northwest corner of Wyoming, with small portions extending into Montana and Idaho. It was established by the 42nd U ...

's geological history these colossal events have been recorded numerous times and have been found to have created new hills and shaped parts of the landscape. The largest hydrothermal explosion ever documented was located near the northern edge of Yellowstone Lake, on an embankment commonly known as "Mary Bay". Now consisting of a 1.5 mile crater, it was formed relatively recently, approximately 13,800 years ago. It is believed this crater was formed by a sequence of several hydrothermal explosions in a short time. What triggered this series of events has not yet been clearly established, but

volcanologist A volcanologist, or volcano scientist, is a geologist who focuses on understanding the formation and eruptive activity of volcanoes. Volcanologists frequently visit volcanoes, sometimes active ones, to observe and monitor volcanic eruptions, col ...

s believe a large earthquake could have played a role by accelerating the melting of nearby glaciers and thus depressurizing the hydrothermal system. Alternatively, rapid changes in the level of Yellowstone Lake may have been responsible.

Recent explosions

Most of Yellowstone's recent large hydrothermal explosions have been the consequence of sudden changes of pressure deep within the hydrothermal system. Generally, these larger explosions have created craters in a north–south pattern (between Norris and

Mammoth Hot Springs Mammoth Hot Springs is a large complex of hot springs on a hill of travertine in Yellowstone National Park adjacent to Fort Yellowstone and the Mammoth Hot Springs Historic District. It was created over thousands of years as hot water from the ...

). It is estimated that all of the known hydrothermal craters were created between 14,000 and 3,000 years ago. Volcanologists believe no magma has ever broken through the fragile crust of Yellowstone Park or stirred the movement of magma in the reservoir beneath Yellowstone. Several small hydrothermal explosions have been recorded since the opening of Yellowstone National Park. During the 1880s, Excelsior Geyser in Midway Geyser Basin was known for significant hydrothermal explosions. Other explosions have been linked to seismic events, such as during the 1959 Hebgen Lake earthquake, while others are linked to changes in plumbing below geysers or hot springs, such as the 1989 explosion at Porkchop Geyser in the Norris Geyser Basin. Small hydrothermal eruptions occur nearly yearly, although many occur in Yellowstone's backcountry. On 23 July 2024, a small hydrothermal explosion was witnessed by several tourists coming from the Black Diamond Pool hot spring in Biscuit Basin. The explosion, probably caused by a change in the plumbing under the hot spring, launched a plume of water and rock fragments into the air. Although there were no injuries, the explosion forced the closure of Biscuit Basin for the rest of the 2024 season.

References

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External links