Hot spring

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Grand Prismatic Spring and Midway Geyser Basin in Yellowstone National Park Aerial view of Grand Prismatic (23428929375).jpg
Grand Prismatic Spring and Midway Geyser Basin in Yellowstone National Park

A hot spring, hydrothermal spring, or geothermal spring is a spring produced by the emergence of geothermally heated groundwater onto the surface of the Earth. The groundwater is heated either by shallow bodies of magma (molten rock) or by circulation through faults to hot rock deep in the Earth's crust. In either case, the ultimate source of the heat is radioactive decay of naturally occurring radioactive elements in the Earth's mantle, the layer beneath the crust.


Hot spring water often contains large amounts of dissolved minerals. The chemistry of hot springs ranges from acid sulfate springs with a pH as low as 0.8, to alkaline chloride springs saturated with silica, to bicarbonate springs saturated with carbon dioxide and carbonate minerals. Some springs also contain abundant dissolved iron. The minerals brought to the surface in hot springs often feed communities of extremophiles, microorganisms adopted to extreme conditions, and it is possible that life on Earth had its origin in hot springs. [1] [2]

Humans have made use of hot springs for bathing, relaxation, or medical therapy for thousands of years. However, some are hot enough that immersion can be harmful, leading to scalding and, potentially, death. [3]


There is no universally accepted definition of a hot spring. For example, one can find the phrase hot spring defined as

Hot Springs in Rio Quente, Brazil. Rio Quente 16 (27822967745).jpg
Hot Springs in Rio Quente, Brazil.

The related term "warm spring" is defined as a spring with water temperature less than a hot spring by many sources, although Pentecost et al. (2003) suggest that the phrase "warm spring" is not useful and should be avoided. [9] The US NOAA Geophysical Data Center defines a "warm spring" as a spring with water between 20 and 50 °C (68 and 122 °F).

Sources of heat

Water issuing from a hot spring is heated geothermally, that is, with heat produced from the Earth's mantle. This takes place in two ways. In areas of high volcanic activity, magma (molten rock) may be present at shallow depths in the Earth's crust. Groundwater is heated by these shallow magma bodies and rises to the surface to emerge at a hot spring. However, even in areas that do not experience volcanic activity, the temperature of rocks within the earth increases with depth. The rate of temperature increase with depth is known as the geothermal gradient. If water percolates deeply enough into the crust, it will be heated as it comes into contact with hot rock. This generally takes place along faults, where shattered rock beds provide easy paths for water to circulate to greater depths. [18]

Much of the heat is created by decay of naturally radioactive elements. An estimated 45 to 90 percent of the heat escaping from the Earth originates from radioactive decay of elements mainly located in the mantle. [19] [20] [21] The major heat-producing isotopes in the Earth are potassium-40, uranium-238, uranium-235, and thorium-232. [22] In areas with no volcanic activity, this heat flows through the crust by a slow process of thermal conduction, but in volcanic areas, the heat is carried to the surface more rapidly by bodies of magma. [23]

The radiogenic heat from the decay of U and Th are now the major contributors to the earth's internal heat budget. Evolution of Earth's radiogenic heat.svg
The radiogenic heat from the decay of U and Th are now the major contributors to the earth's internal heat budget.

A hot spring that periodically jets water and steam is called a geyser. In active volcanic zones such as Yellowstone National Park, magma may be present at shallow depths. If a hot spring is connected to a large natural cistern close to such a magma body, the magma may superheat the water in the cistern, raising its temperature above the normal boiling point. The water will not immediately boil, because the weight of the water column above the cistern pressurizes the cistern and suppresses boiling. However, as the superheated water expands, some of the water will emerge at the surface, reducing pressure in the cistern. This allows some of the water in the cistern to flash into steam, which forces more water out of the hot spring. This leads to a runaway condition in which a sizable amount of water and steam are forcibly ejected from the hot spring as the cistern is emptied. The cistern then refills with cooler water, and the cycle repeats. [24] [25]

Geysers require both a natural cistern and an abundant source of cooler water to refill the cistern after each eruption of the geyser. If the water supply is less abundant, so that the water is boiled as fast as it can accumulate and only reaches the surface in the form of steam, the result is a fumarole. If the water is mixed with mud and clay, the result is a mud pot. [24] [26]

An example of a non-volcanic warm spring is Warm Springs, Georgia (frequented for its therapeutic effects by paraplegic U.S. President Franklin D. Roosevelt, who built the Little White House there). Here the groundwater originates as rain and snow (meteoric water) falling on the nearby mountains, which penetrates a particular formation (Hollis Quartzite) to a depth of 3,000 feet (910 m) and is heated by the normal geothermal gradient. [27]


Hammam Maskhoutine in Algeria, an example of a bicarbonate hot spring GM Guelma Hammam Challala01.jpg
Hammam Maskhoutine in Algeria, an example of a bicarbonate hot spring

Because heated water can hold more dissolved solids than cold water, the water that issues from hot springs often has a very high mineral content, containing everything from calcium to lithium and even radium. [28] The overall chemistry of hot springs varies from alkaline chloride to acid sulfate to bicarbonate to iron-rich, each of which defines an end member of a range of possible hot spring chemistries. [29] [30]

Alkaline chloride hot springs are fed by hydrothermal fluids that form when groundwater containing dissolved chloride salts reacts with silicate rocks at high temperature. These springs have nearly neutral pH but are saturated with silica (SiO
). The solubility of silica depends strongly upon temperature, so upon cooling, the silica is deposited as geyserite, a form of opal (opal-A: SiO
). [31] This process is slow enough that geyserite is not all deposited immediately around the vent, but tends to build up a low, broad platform for some distance around the spring opening. [32] [33] [34]

Acid sulfate hot springs are fed by hydrothermal fluids rich in hydrogen sulfide (H
), which is oxidized to form sulfuric acid, H
. [32] The pH of the fluids is thereby lowered to values as low as 0.8. [35] The acid reacts with rock to alter it to clay minerals, oxide minerals, and a residue of silica. [30]

Bicarbonate hot springs are fed by hydrothermal fluids that form when carbon dioxide (CO
) and groundwater react with carbonate rocks. [32] When the fluids reach the surface, CO
is rapidly lost and carbonate minerals precipitate as travertine, so that bicarbonate hot springs tend to form high-relief structures around their openings. [30]

Iron-rich springs are characterized by the presence of microbial communities that produce clumps of oxidized iron from iron in the hydrothermal fluids feeding the spring. [36] [30]

Some hot springs produce fluids that are intermediate in chemistry between these extremes. For example, mixed acid-sulfate-chloride hot springs are intermediate between acid sulfate and alkaline chloride springs and may form by mixing of acid sulfate and alkaline chloride fluids. They deposit geyserite, but in smaller quantities than alkaline chloride springs. [32]

Flow rates

Deildartunguhver, Iceland: the highest flow hot spring in Europe Islande source Deildartunguhver.jpg
Deildartunguhver, Iceland: the highest flow hot spring in Europe

Hot springs range in flow rate from the tiniest "seeps" to veritable rivers of hot water. Sometimes there is enough pressure that the water shoots upward in a geyser, or fountain.

High-flow hot springs

There are many claims in the literature about the flow rates of hot springs. There are many more high flow non-thermal springs than geothermal springs. Springs with high flow rates include:

Hot spring ecosystems

Algal mats growing in the Map of Africa hot pool, Orakei Korako, New Zealand Algal mats on hot pool, Orakei Korako 1.jpg
Algal mats growing in the Map of Africa hot pool, Orakei Korako, New Zealand

Hot springs often host communities of microorganisms adapted to life in hot, mineral-laden water. These include thermophiles, which are a type of extremophile that thrives at high temperatures, between 45 and 80 °C (113 and 176 °F). [40] Further from the vent, where the water has had time to cool and precipitate part of its mineral load, conditions favor organisms adapted to less extreme conditions. This produces a succession of microbial communities as one moves away from the vent, which in some respects resembles the successive stages in the evolution of early life. [41]

For example, in a bicarbonate hot spring, the community of organisms immediately around the vent is dominated by filamentous thermophilic bacteria, such as Aquifex and other Aquificales, that oxidize sulfide and hydrogen to obtain energy for their life processes. Further from the vent, where water temperatures have dropped below 60 °C (140 °F), the surface is covered with microbial mats 1 centimetre (0.39 in) thick that are dominated by cyanobacteria, such as Spirulina , Oscillatoria , and Synechococcus , [42] and green sulfur bacteria such as Chloroflexus . These organisms are all capable of photosynthesis, though green sulfur bacteria produce sulfur rather than oxygen during photosynthesis. Still further from the vent, where temperatures drop below 45 °C (113 °F), conditions are favorable for a complex community of microorganisms that includes Spirulina, Calothrix , diatoms and other single-celled eukaryotes, and grazing insects and protozoans. As temperatures drop close to those of the surroundings, higher plants appear. [41]

Alkali chloride hot springs show a similar succession of communities of organisms, with various thermophilic bacteria and archaea in the hottest parts of the vent. Acid sulfate hot springs show a somewhat different succession of microorganisms, dominated by acid-tolerant algae (such as members of Cyanidiophyceae), fungi, and diatoms. [32] Iron-rich hot springs contain communities of photosynthetic organisms that oxidize reduced (ferrous) iron to oxidized (ferric) iron. [43]

Hot springs are a dependable source of water that provides a rich chemical environment. This includes reduced chemical species that microorganisms can oxidize as a source of energy. In contrast with "black smokers" (hydrothermal vents on the ocean floor), hot springs produce fluids at less extreme temperatures, and they experience cycles of wetting and drying that promote formation of simple organic molecules. For these reasons, it has been hypothesized that hot springs may be the place of origin of life on Earth. [41] [30]

Human uses

Macaques enjoying an open air hot spring or "onsen" in Nagano Jigokudani hotspring in Nagano Japan 001.jpg
Macaques enjoying an open air hot spring or "onsen" in Nagano
Winter bathing at Tsuru-no-yu roten-buro in Nyuto, Akita Tsurunoyu onsen rotenburo2.JPG
Winter bathing at Tsuru-no-yu roten-buro in Nyūtō, Akita

Hot springs have been enjoyed by humans for thousands of years. [44] Even macaques, which are nonhuman primates, are known to have extended their northern range into Japan by making use of hot springs to protect themselves from cold stress. [45] Hot spring baths ( onsen ) have been in use in Japan for at least two thousand years, traditionally for cleanliness and relaxation, but increasingly for their therapeutic value. [46] In the Homeric Age of Greece (ca. 1000 BCE), baths were primarily for hygiene, but by the time of Hippocrates (ca. 460 BCE), hot springs were credited with healing power. The popularity of hot springs has fluctuated over the centuries since, but they are now popular around the world. [47]

Therapeutic uses

Because of both the folklore and the claimed medical value attributed to some hot springs, they are often popular tourist destinations, and locations for rehabilitation clinics for those with disabilities. [48] [49] [50] However, the scientific basis for therapeutic bathing in hot springs is uncertain. Hot bath therapy for lead poisoning was common and reportedly highly successful in the 18th and 19th centuries, and may have been due to diuresis (increased production of urine) from sitting in hot water, which increased excretion of lead; better food and isolation from lead sources; and increased intake of calcium and iron. Significant improvement in patients suffering from rheumatoid arthritis and ankylosing spondylitis have been reported in studies of spa therapy, but these suffer from methodological problems, such as the obvious impracticality of placebo-controlled studies (in which a patient does not know if he is receiving the therapy). As a result, the therapeutic effectiveness of hot spring therapy remains uncertain. [47]


Hot springs in volcanic areas are often at or near the boiling point. People have been seriously scalded and even killed by accidentally or intentionally entering these springs. [51] [52] [53]

Some hot springs microbiota are infectious to humans:


The customs and practices observed differ depending on the hot spring. It is common practice that bathers should wash before entering the water so as not to contaminate the water (with/without soap). [60] In many countries, like Japan, it is required to enter the hot spring with no clothes on, including swimwear. Often there are different facilities or times for men and women, but mixed onsen do exist. [61] In some countries, if it is a public hot spring, swimwear is required. [62] [63]


Distribution of geothermal springs in the US Geothermal springs map US.png
Distribution of geothermal springs in the US

There are hot springs in many places and on all continents of the world. Countries that are renowned for their hot springs include China, Costa Rica, Iceland, Iran, Japan, New Zealand, Brazil, Peru, Taiwan, Turkey, and the United States, but there are hot springs in many other places as well:

See also

Related Research Articles

Geyser Hot spring characterized by intermittent discharge of water ejected turbulently and accompanied by steam

A geyser is a spring characterized by an intermittent discharge of water ejected turbulently and accompanied by steam. As a fairly rare phenomenon, the formation of geysers is due to particular hydrogeological conditions that exist only in a few places on Earth. Generally all geyser field sites are located near active volcanic areas, and the geyser effect is due to the proximity of magma. Generally, surface water works its way down to an average depth of around 2,000 metres (6,600 ft) where it contacts hot rocks. The resultant boiling of the pressurized water results in the geyser effect of hot water and steam spraying out of the geyser's surface vent.

Volcano Rupture in the crust of a planet that allows lava, ash, and gases to escape from below the surface

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.

Magma Natural material found beneath the surface of Earth

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 natural satellites. Besides molten rock, magma may also contain suspended crystals and gas bubbles.

Long Valley Caldera

Long Valley Caldera is a depression in eastern California that is adjacent to Mammoth Mountain. The valley is one of the Earth's largest calderas, measuring about 20 mi (32 km) long (east-west), 11 mi (18 km) wide (north-south), and up to 3,000 ft (910 m) deep.

Geothermal areas of Yellowstone Geyser basins and other geothermal features in Yellowstone National Park

The geothermal areas of Yellowstone include several geyser basins in Yellowstone National Park as well as other geothermal features such as hot springs, mud pots, and fumaroles. The number of thermal features in Yellowstone is estimated at 10,000. A study that was completed in 2011 found that a total of 1,283 geysers have erupted in Yellowstone, 465 of which are active during an average year. These are distributed among nine geyser basins, with a few geysers found in smaller thermal areas throughout the Park. The number of geysers in each geyser basin are as follows: Upper Geyser Basin (410), Midway Geyser Basin (59), Lower Geyser Basin (283), Norris Geyser Basin (193), West Thumb Geyser Basin (84), Gibbon Geyser Basin (24), Lone Star Geyser Basin (21), Shoshone Geyser Basin (107), Heart Lake Geyser Basin (69), other areas (33). Although famous large geysers like Old Faithful are part of the total, most of Yellowstone's geysers are small, erupting to only a foot or two. The hydrothermal system that supplies the geysers with hot water sits within an ancient active caldera. Many of the thermal features in Yellowstone build up sinter, geyserite, or travertine deposits around and within them.

Hydrothermal circulation in its most general sense is the circulation of hot water. Hydrothermal circulation occurs most often in the vicinity of sources of heat within the Earth's crust. In general, this occurs near volcanic activity, but can occur in the deep crust related to the intrusion of granite, or as the result of orogeny or metamorphism.

Geothermal areas in Lassen Volcanic National Park

The geothermal areas in Lassen Volcanic National Park include several groups of hot springs and fumaroles, as remnants of former volcanic activity, exist in Lassen Volcanic National Park. Most of these lie in or are closely adjacent to Mount Tehama's caldera. Bumpass Hell is the most spectacular of these, but others of importance are Sulphur Works, Little Hot Springs Valley, Boiling Springs Lake and Devil's Kitchen. In each thermal area, the highest temperature of water generally is close to the boiling temperature at the altitude of the particular spring or fumarole — 198 °F (92 °C) at Bumpass Hell and 191 °F (88 °C) on the northwest flanks of Lassen Peak. Temperatures as high as 230 °F (110 °C) have been recorded in the park.

El Tatio Geyser field located in the Andes Mountains, Chile

El Tatio is a geyser field located in the Andes Mountains of northern Chile at 4,320 metres (14,170 ft) above mean sea level. Various etymologies have been proposed for the name "El Tatio", which might mean "oven" or "grandfather". It is the third-largest geyser field in the world and the largest in the Southern Hemisphere.

Geothermal heating Use of geothermal energy for heating

Geothermal heating is the direct use of geothermal energy for some heating applications. Humans have taken advantage of geothermal heat this way since the Paleolithic era. Approximately seventy countries made direct use of a total of 270 PJ of geothermal heating in 2004. As of 2007, 28 GW of geothermal heating capacity is installed around the world, satisfying 0.07% of global primary energy consumption. Thermal efficiency is high since no energy conversion is needed, but capacity factors tend to be low since the heat is mostly needed in the winter.

Steamboat Springs (Nevada)

Steamboat Springs is a small volcanic field of rhyolitic lava domes and flows in western Nevada, located south of Reno. There is extensive geothermal activity in the area, including numerous hot springs, steam vents, and fumaroles. The residential portions of this area, located mostly east of Steamboat Creek and south of modern-day SR 341, are now known simply as Steamboat.

Orakei Korako

Orakei Korako is a highly active geothermal area most notable for its series of fault-stepped sinter terraces, located in a valley north of Taupo on the banks of the Waikato River in the Taupo Volcanic Zone, New Zealand. It is also known as "The Hidden Valley".

Volcanic gas

Volcanic gases are gases given off by active volcanoes. These include gases trapped in cavities (vesicles) in volcanic rocks, dissolved or dissociated gases in magma and lava, or gases emanating from lava, from volcanic craters or vents. Volcanic gases can also be emitted through ground water heated by volcanic action.

Taftan (volcano) Volcano mountain in Iran

Taftan is an active stratovolcano in south-eastern Iran in the Sistan and Baluchestan province. With variable heights reported, all around 4,000 metres (13,000 ft) above sea level, it is the highest mountain in south-eastern Iran. The nearest city is Khash.

Hot Creek (Mono County)

Hot Creek, starting as Mammoth Creek, is a stream in Mono County of eastern California, in the Western United States. It is within the Inyo National Forest.

Waimangu Volcanic Rift Valley Volcanic Valley in New Zealand

The Waimangu Volcanic Rift Valley is the hydrothermal system created on 10 June 1886 by the volcanic eruption of Mount Tarawera, on the North Island of New Zealand. It encompasses Lake Rotomahana, the site of the Pink and White Terraces, as well as the location of the Waimangu Geyser, which was active from 1900 to 1904. The area has been increasingly accessible as a tourist attraction and contains Frying Pan Lake, which is the largest hot spring in the world, and the steaming and usually pale blue Inferno Crater Lake, the largest geyser-like feature in the world although the geyser itself cannot be seen since it plays at the bottom of the lake.

Endeavour Hydrothermal Vents Group of hydrothermal vents in the northeastern Pacific Ocean southwest of Vancouver Island, British Columbia, Canada

The Endeavor Hydrothermal Vents are a group of hydrothermal vents in the northeastern Pacific Ocean, located 260 kilometres (160 mi) southwest of Vancouver Island, British Columbia, Canada.

Lava Molten rock expelled by a volcano during an eruption

Lava is molten rock (magma) that has been expelled from the interior of a terrestrial planet or a moon. Magma is generated by the internal heat of the planet or moon and it is erupted as lava at volcanoes or through fractures in the crust, usually at temperatures from 800 to 1,200 °C. The volcanic rock resulting from subsequent cooling is also often described as lava.

Mars may contain ores that would be very useful to potential colonists. The abundance of volcanic features together with widespread cratering are strong evidence for a variety of ores. While nothing may be found on Mars that would justify the high cost of transport to Earth, the more ores that future colonists can obtain from Mars, the easier it would be to build colonies there.

Hydrothermal mineral deposits are accumulations of valuable minerals which formed from hot waters circulating in Earth's crust through fractures. They eventually create rich-metallic fluids concentrated in a selected volume of rock, which become supersaturated and then precipitate ore minerals. In some occurrences, minerals can be extracted at a profit by mining. Discovery of mineral deposits consumes considerable time and resources and only about one in every one thousand prospects explored by companies are eventually developed into a mine. A mineral deposit is any geologically significant concentration of an economically useful rock or mineral present in a specified area. The presence of a known but unexploited mineral deposit implies a lack of evidence for profitable extraction.


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