Aerial view of Grand Prismatic (23428929375)

A hot spring, hydrothermal spring, or geothermal spring is a

spring Spring(s) may refer to: Common uses * Spring (season), a season of the year * Spring (device), a mechanical device that stores energy * Spring (hydrology), a natural source of water * Spring (mathematics), a geometric surface in the shape of a h ...

produced by the emergence of geothermally heated

groundwater Groundwater is the water present beneath Earth's surface in rock and Pore space in soil, soil pore spaces and in the fractures of stratum, rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit ...

onto the surface of the Earth. The groundwater is heated either by shallow bodies of

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 ...

(molten rock) or by circulation through faults to hot rock deep in the

Earth's crust Earth's crust is Earth's thin outer shell of rock, referring to less than 1% of Earth's radius and volume. It is the top component of the lithosphere, a division of Earth's layers that includes the crust and the upper part of the mantle. The ...

. In either case, the ultimate source of the heat is

radioactive decay Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consid ...

of naturally occurring radioactive elements in the

Earth's mantle Earth's mantle is a layer of silicate rock between the crust and the outer core. It has a mass of 4.01 × 1024 kg and thus makes up 67% of the mass of Earth. It has a thickness of making up about 84% of Earth's volume. It is predominantly so ...

, 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 Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...

, to bicarbonate springs saturated with

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 ...

and carbonate minerals. Some springs also contain abundant dissolved iron. The minerals brought to the surface in hot springs often feed communities of

extremophiles An extremophile (from Latin ' meaning "extreme" and Greek ' () meaning "love") is an organism that is able to live (or in some cases thrive) in extreme environments, i.e. environments that make survival challenging such as due to extreme tempe ...

, microorganisms adapted to extreme conditions, and it is possible that life on Earth had its origin in hot springs. 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.

Definitions

There is no universally accepted definition of a hot spring. For example, one can find the phrase ''hot spring'' defined as * any spring heated by geothermal activity * a spring with water temperatures above its surroundings * a natural spring with water temperature above

human body temperature Normal human body-temperature (normothermia, euthermia) is the typical temperature range found in humans. The normal human body temperature range is typically stated as . Human body temperature varies. It depends on sex, age, time of day, exer ...

(normally about ) provides a critical discussion of the definition of a hot spring. Rio Quente 16 (27822967745)

* a natural spring of water whose temperature is greater than * a type of thermal spring whose water temperature is usually or more above mean air temperature. * a spring with water temperatures above 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. The US

NOAA The National Oceanic and Atmospheric Administration (abbreviated as NOAA ) is an United States scientific and regulatory agency within the United States Department of Commerce that forecasts weather, monitors oceanic and atmospheric conditio ...

Geophysical Data Center defines a "warm spring" as a spring with water between .

Sources of heat

Water issuing from a hot spring is heated geothermally, that is, with

heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is ...

produced from the

. This takes place in two ways. In areas of high volcanic activity,

(molten rock) may be present at shallow depths in the

. 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 Geothermal gradient is the rate of temperature change with respect to increasing depth in Earth's interior. As a general rule, the crust temperature rises with depth due to the heat flow from the much hotter mantle; away from tectonic plate bo ...

. 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. 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. The major heat-producing isotopes in the Earth are

potassium-40 Potassium-40 (40K) is a radioactive isotope of potassium which has a long half-life of 1.25 billion years. It makes up about 0.012% (120 ppm) of the total amount of potassium found in nature. Potassium-40 undergoes three types of radioactive d ...

uranium-238 Uranium-238 (238U or U-238) is the most common isotope of uranium found in nature, with a relative abundance of 99%. Unlike uranium-235, it is non-fissile, which means it cannot sustain a chain reaction in a thermal-neutron reactor. However ...

uranium-235 Uranium-235 (235U or U-235) is an isotope of uranium making up about 0.72% of natural uranium. Unlike the predominant isotope uranium-238, it is fissile, i.e., it can sustain a nuclear chain reaction. It is the only fissile isotope that exi ...

, and thorium-232. In areas with no volcanic activity, this heat flows through the crust by a slow process of

thermal conduction Conduction is the process by which heat is transferred from the hotter end to the colder end of an object. The ability of the object to conduct heat is known as its ''thermal conductivity'', and is denoted . Heat spontaneously flows along a te ...

, but in volcanic areas, the heat is carried to the surface more rapidly by bodies of magma. Evolution of Earth's radiogenic heat

A hot spring that periodically jets water and steam is called a

geyser 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 i ...

. In active volcanic zones such as

Yellowstone National Park Yellowstone National Park is an American national park located in the western United States, largely in the northwest corner of Wyoming and extending into Montana and Idaho. It was established by the 42nd U.S. Congress with the Yellowst ...

, 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. 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 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 ...

, the result is a

fumarole A fumarole (or fumerole) is a vent in the surface of the Earth or other 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 ...

. If the water is mixed with mud and

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay pa ...

, the result is a

mud pot A mudpot, or mud pool, is a sort of acidic hot spring, or fumarole, with limited water. It usually takes the form of a pool of bubbling mud. The acid and microorganisms decompose surrounding rock into clay and mud. Description The mud of a mud ...

. An example of a non-volcanic warm spring is

Warm Springs, Georgia Warm Springs is a city in Meriwether County, Georgia, United States. The population was 425 at the 2010 census. History Warm Springs, originally named Bullochville (after the Bulloch family, which began after Stephen Bullock moved to Meriwethe ...

(frequented for its therapeutic effects by

paraplegic Paraplegia, or paraparesis, is an impairment in motor or sensory function of the lower extremities. The word comes from Ionic Greek () "half-stricken". It is usually caused by spinal cord injury or a congenital condition that affects the neura ...

U.S. President Franklin D. Roosevelt, who built the

Little White House The Little White House was the personal retreat of Franklin D. Roosevelt, the 32nd President of the United States, located in the Historic District of Warm Springs, Georgia. He first came to Warm Springs (formerly known as Bullochville) in 19 ...

there). Here the groundwater originates as rain and snow (

meteoric water Meteoric water is the water derived from precipitation (snow and rain). This includes water from lakes, rivers, and icemelts, which all originate from precipitation indirectly. While the bulk of rainwater or meltwater from snow and ice reaches the ...

) falling on the nearby mountains, which penetrates a particular

formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondar ...

( Hollis Quartzite) to a depth of and is heated by the normal geothermal gradient.

Chemistry

Because heated water can hold more dissolved

solid Solid is one of the four fundamental states of matter (the others being liquid, gas, and plasma). The molecules in a solid are closely packed together and contain the least amount of kinetic energy. A solid is characterized by structur ...

s than cold water, the water that issues from hot springs often has a very high

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...

content, containing everything from

calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar ...

lithium Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense soli ...

and even

radium Radium is a chemical element with the symbol Ra and atomic number 88. It is the sixth element in group 2 of the periodic table, also known as the alkaline earth metals. Pure radium is silvery-white, but it readily reacts with nitrogen (rat ...

. Analytical results for Takhini Hot Springs geothermal water: 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. Alkaline chloride hot springs are fed by hydrothermal fluids that form when groundwater containing dissolved

chloride The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride s ...

salts reacts with silicate rocks at high temperature. These springs have nearly neutral pH but are saturated with

(). The solubility of silica depends strongly upon temperature, so upon cooling, the silica is deposited as geyserite, a form of

opal Opal is a hydrated amorphous form of silica (SiO2·''n''H2O); its water content may range from 3 to 21% by weight, but is usually between 6 and 10%. Due to its amorphous property, it is classified as a mineraloid, unlike crystalline form ...

(opal-A: ). 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. Acid sulfate hot springs are fed by hydrothermal fluids rich in

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 ...

(), which is oxidized to form

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular fo ...

, . The pH of the fluids is thereby lowered to values as low as 0.8. The acid reacts with rock to alter it to

clay mineral Clay minerals are hydrous aluminium phyllosilicates (e.g. kaolin, Al2 Si2 O5( OH)4), sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations found on or near some planetary surfaces. Clay minera ...

oxide minerals The oxide mineral class includes those minerals in which the oxide anion (O2−) is bonded to one or more metal alloys. The hydroxide-bearing minerals are typically included in the oxide class. The minerals with complex anion groups such as the si ...

, and a residue of silica. Bicarbonate hot springs are fed by hydrothermal fluids that form when

() and groundwater react with

carbonate rocks Carbonate rocks are a class of sedimentary rocks composed primarily of carbonate minerals. The two major types are limestone, which is composed of calcite or aragonite (different crystal forms of CaCO3), and dolomite rock (also known as doloston ...

. When the fluids reach the surface, is rapidly lost and carbonate minerals precipitate as

travertine Travertine ( ) is a form of terrestrial limestone deposited around mineral springs, especially hot springs. It often has a fibrous or concentric appearance and exists in white, tan, cream-colored, and even rusty varieties. It is formed by a p ...

, so that bicarbonate hot springs tend to form high-relief structures around their openings. 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. 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.

Flow rates

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

, or

fountain A fountain, from the Latin "fons" (genitive "fontis"), meaning source or spring, is a decorative reservoir used for discharging water. It is also a structure that jets water into the air for a decorative or dramatic effect. Fountains were ori ...

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: * The Dalhousie Springs complex in Australia had a peak total flow of more than 23,000 liters/second in 1915, giving the average spring in the complex an output of more than 325 liters/second. This has been reduced now to a peak total flow of 17,370 liters/second so the average spring has a peak output of about 250 liters/second. * natural iron hot spring

The 2,850 hot springs of

Beppu is a city in Ōita Prefecture on the island of Kyushu, Japan. As of March 31, 2017, the city had a population of 122,643Kokonoe in Japan produce 1,028 liters/second, which gives the average hot spring a flow of 3.39 liters/second. *

Ōita Prefecture is a prefecture of Japan located on the island of Kyūshū. Ōita Prefecture has a population of 1,136,245 (1 June 2019) and has a geographic area of 6,340 km2 (2,448 sq mi). Ōita Prefecture borders Fukuoka Prefecture to the northwest, Kum ...

has 4,762 hot springs, with a total flow of 4,437 liters/second, so the average hot spring flow is 0.93 liters/second. * The highest flow rate hot spring in Japan is the

Tamagawa Hot Spring is a hot spring located in the city of Semboku, Akita in northern Japan. Water profile The spring has a flow of 9000 liters/minute and feeds a 3-meter wide stream with a temperature of 98 °C. The water from Tamagawa Hot Spring is extre ...

Akita Prefecture is a prefecture of Japan located in the Tōhoku region of Honshu.Nussbaum, Louis-Frédéric. (2005). "Provinces and prefectures" in ; "Tōhoku" in . Its population is approximately 966,000 (as of 1 October 2019) and its geographic area is 11,6 ...

, which has a flow rate of 150 liters/second. The Tamagawa Hot Spring feeds a wide stream with a temperature of . * The most famous hot springs of

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

Caldas Novas Caldas Novas () is a Brazilian municipality in the state of Goiás. It is considered by many to be the largest hydro-thermal resort in the world. Location Caldas Novas is located 170 km south of state capital, Goiânia, with good roads link ...

("New Hot Springs" in

Portuguese Portuguese may refer to: * anything of, from, or related to the country and nation of Portugal ** Portuguese cuisine, traditional foods ** Portuguese language, a Romance language *** Portuguese dialects, variants of the Portuguese language ** Portu ...

) are tapped by 86 wells, from which 333 liters/second are pumped for 14 hours per day. This corresponds to a peak average flow rate of 3.89 liters/second per well. * In

Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and ...

, there are 33 recognized "magnitude one springs" (having a flow in excess of ).

Silver Springs, Florida Silver Springs is an unincorporated community and census-designated place (CDP) in Marion County, Florida, United States. It is the site of Silver Springs, a group of artesian springs and a historic tourist attraction that is now part of Si ...

has a flow of more than . * The

Excelsior Geyser Excelsior Geyser Crater, formerly known as Excelsior Geyser, is a dormant fountain-type geyser in the Midway Geyser Basin of Yellowstone National Park in the United States. Excelsior was named by the Hayden Geological Survey of 1871. Description ...

Crater in

yields about . * Evans Plunge in Hot Springs, South Dakota has a flow rate of of spring water. The Plunge, built in 1890, is the world's largest natural warm water indoor swimming pool. * The hot spring of

Saturnia Saturnia () is a spa town in Tuscany in north-central Italy that has been inhabited since ancient times. It is a ''frazione'' of the '' comune'' of Manciano, in the province of Grosseto. Famous for the spa which gives it its name, its population ...

, Italy with around 500 liters a second * Lava Hot Springs in

Idaho Idaho ( ) is a U.S. state, state in the Pacific Northwest region of the Western United States. To the north, it shares a small portion of the Canada–United States border with the province of British Columbia. It borders the states of Monta ...

has a flow of 130 liters/second. *

Glenwood Springs Glenwood Springs is a home rule municipality that is the county seat of Garfield County, Colorado, United States. The city population was 9,963 at the 2020 United States Census. Glenwood Springs is located at the confluence of the Roaring Fork ...

Colorado Colorado (, other variants) is a state in the Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the western edge of the ...

has a flow of 143 liters/second. * Elizabeth Springs in western

Queensland ) , nickname = Sunshine State , image_map = Queensland in Australia.svg , map_caption = Location of Queensland in Australia , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , establishe ...

, Australia might have had a flow of 158 liters/second in the late 19th century, but now has a flow of about 5 liters/second. *

Deildartunguhver Deildartunguhver () is a hot spring in Reykholtsdalur, Iceland. It is characterized by a very high flow rate for a hot spring (180 liters/second) and water emerges at 97 °C. It is the highest-flow hot spring in Europe. Some of the water is ...

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 ...

has a flow of 180 liters/second. * There are at least three hot springs in the Nage region south west of

Bajawa Bajawa is a town of Flores, Indonesia and the capital of the Ngada Regency. Ngada Regency is part of East Nusa Tenggara province and located to the east of Ruteng. Bajawa features natural hot springs which are used for bathing and volcanic ...

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 ...

that collectively produce more than 453.6 liters/second. * There are another three large hot springs (Mengeruda, Wae Bana and Piga) north east of Bajawa,

that together produce more than 450 liters/second of hot water. * In Yukon's Boreal Forest, 25 minutes north-west of Whitehorse in northern Canada, Takhini Hot Springs flows out of the Earth's interior at and 47 °C (118 °F) year-round.

Ecosystems

Hot springs often host communities of microorganisms adapted to life in hot, mineral-laden water. These include

thermophile A thermophile is an organism—a type of extremophile—that thrives at relatively high temperatures, between . Many thermophiles are archaea, though they can be bacteria or fungi. Thermophilic eubacteria are suggested to have been among the earl ...

s, which are a type of

extremophile An extremophile (from Latin ' meaning "extreme" and Greek ' () meaning "love") is an organism that is able to live (or in some cases thrive) in extreme environments, i.e. environments that make survival challenging such as due to extreme tem ...

that thrives at high temperatures, between . 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. For example, in a bicarbonate hot spring, the community of organisms immediately around the vent is dominated by filamentous thermophilic

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...

, such as ''

Aquifex ''Aquifex'' is a bacterial genus, belonging to phylum Aquificota. There is one species of ''Aquifex'' with a validly published name – '' A. pyrophilus'' – but "'' A. aeolicus''" is sometimes considered as species though it has no standing as ...

'' and other

Aquificales The ''Aquificota'' phylum (biology), phylum is a diverse collection of bacteria that live in harsh environmental settings. The name ''Aquificota'' was given to this phylum based on an early genus identified within this group, ''Aquifex'' (“wate ...

, that oxidize sulfide and hydrogen to obtain energy for their life processes. Further from the vent, where water temperatures have dropped below , the surface is covered with microbial mats thick that are dominated by

cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, bl ...

, such as '' Spirulina'', ''

Oscillatoria ''Oscillatoria'' is a genus of filamentous cyanobacterium which is often found in freshwater environments, such as hot springs, and appears blue-green. Its name refers to the oscillating motion of its filaments as they slide against each other ...

'', and ''

Synechococcus ''Synechococcus'' (from the Greek ''synechos'', in succession, and the Greek ''kokkos'', granule) is a unicellular cyanobacterium that is very widespread in the marine environment. Its size varies from 0.8 to 1.5 µm. The photosynthetic c ...

'', and

green sulfur bacteria The green sulfur bacteria are a phylum of obligately anaerobic photoautotrophic bacteria that metabolize sulfur. Green sulfur bacteria are nonmotile (except ''Chloroherpeton thalassium'', which may glide) and capable of anoxygenic photosynthe ...

such as ''

Chloroflexus Chloroflexales is an order of bacteria in the class Chloroflexia. Taxonomy The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Center for Biotechnology Information (NCBI). * ...

''. These organisms are all capable of

photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in ...

, though green sulfur bacteria produce

sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formul ...

rather than

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...

during photosynthesis. Still further from the vent, where temperatures drop below , conditions are favorable for a complex community of microorganisms that includes ''Spirulina'', '' Calothrix'',

diatoms A diatom (Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising sev ...

and other single-celled

eukaryotes Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacter ...

, and grazing insects and protozoans. As temperatures drop close to those of the surroundings, higher plants appear. Alkali chloride hot springs show a similar succession of communities of organisms, with various thermophilic bacteria and

archaea Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaeba ...

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 A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately fr ...

, and diatoms. Iron-rich hot springs contain communities of photosynthetic organisms that oxidize reduced (

ferrous In chemistry, the adjective Ferrous indicates a compound that contains iron(II), meaning iron in its +2 oxidation state, possibly as the divalent cation Fe2+. It is opposed to " ferric" or iron(III), meaning iron in its +3 oxidation state, suc ...

) iron to oxidized (

ferric In chemistry, iron(III) refers to the element iron in its +3 oxidation state. In ionic compounds (salts), such an atom may occur as a separate cation (positive ion) denoted by Fe3+. The adjective ferric or the prefix ferri- is often used to sp ...

) iron. 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.

Significance to abiogenesis

Hot spring hypothesis

In contrast with "

black smokers A hydrothermal vent is a fissure on the seabed from which geothermally heated water discharges. They are commonly found near volcanically active places, areas where tectonic plates are moving apart at mid-ocean ridges, ocean basins, and hotspot ...

" (hydrothermal vents on the ocean floor), hot springs similar to terrestrial hydrothermal fields at Kamchatka produce fluids having suitable pH and temperature for early cells and biochemical reactions. Dissolved organic compounds were found in hot springs at Kamchatka . Metal sulfides and silica minerals in these environments would act as photocatalysts. They experience cycles of wetting and drying which promote the formation of biopolymers which are then encapsulated in vesicles after rehydration. Solar UV exposure to the environment promotes synthesis to monomeric biomolecules. The ionic composition and concentration of hot springs (K, B, Zn, P, O, S, C, Mn, N, and H) are identical to the cytoplasm of modern cells and possibly to those of the LUCA or early cellular life according to phylogenomic analysis. For these reasons, it has been hypothesized that hot springs may be the place of origin of life on Earth. The evolutionary implications of the hypothesis imply a direct evolutionary pathway to land plants. Where continuous exposure to sunlight leads to the development of photosynthetic properties and later colonize on land and life at hydrothermal vents is suggested to be a later adaptation. Recent experimental studies at hot springs support this hypothesis. They show that fatty acids self-assemble into membranous structures and encapsulate synthesized biomolecules during exposure to UV light and multiple wet-dry cycles at slightly alkaline or acidic hot springs, which would not happen at saltwater conditions as the high concentrations of ionic solutes there would inhibit the formation of membranous structures. David Deamer and Bruce Damer note that these hypothesized prebiotic environments resemble

Charles Darwin Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all species of life have descended ...

's imagined "warm little pond". If life did not emerge at deep sea hydrothermal vents, rather at terrestrial pools, extraterrestrial quinones transported to the environment would generate redox reactions conducive to proton gradients. Without continuous wet-dry cycling to maintain stability of primitive proteins for membrane transport and other biological macromolecules, they would go through hydrolysis in an aquatic environment. Scientists discovered a 3.48 billion year old geyserite that seemingly preserved fossilized microbial life, stromatolites, and biosignatures. Researchers propose pyrophosphite to have been used by early cellular life for energy storage and it might have been a precursor to pyrophosphate. Phosphites, which are present at hot springs, would have bonded together into pyrophosphite within hot springs through wet-dry cycling. Like alkaline hydrothermal vents, the Hakuba Happo hot spring goes through serpentinization, suggesting methanogenic microbial life possibly originated in similar habitats.

Limitations

A problem with the hot spring hypothesis for an origin of life is that phosphate has low solubility in water. Pyrophosphite could have been present within protocells, however all modern life forms use pyrophosphate for energy storage. Kee suggests that pyrophosphate could have been utilized after the emergence of enzymes. Dehydrated conditions would favor phosphorylation of organic compounds and condensation of phosphate to polyphosphate. Another problem is that solar ultraviolet radiation and frequent impacts would have inhibited habitability of early cellular life at hot springs, although biological macromolecules might have underwent selection during exposure to solar ultraviolet radiation and would have been catalyzed by photocatalytic silica minerals and metal sulfides. Carbonaceous meteors during the Late Heavy Bombardment would not have caused cratering on Earth as they would produce fragments upon atmospheric entry. The meteors are estimated to have been 40 to 80 meters in diameter however larger impactors would produce larger craters. Metabolic pathways have not yet been demonstrated at these environments, but the development of proton gradients might have been generated by redox reactions coupled to meteoric quinones or protocell growth. Metabolic reactions in the Wood-Ljungdahl pathway and reverse Krebs cycle have been produced in acidic conditions and thermophilic temperatures in the presence of metals which is consistent with observations of RNA mostly stable at acidic pH.

Human uses

Jigokudani hotspring in Nagano Japan 001

History

Hot springs have been enjoyed by humans for thousands of years. Even

macaques The macaques () constitute a genus (''Macaca'') of gregarious Old World monkeys of the subfamily Cercopithecinae. The 23 species of macaques inhabit ranges throughout Asia, North Africa, and (in one instance) Gibraltar. Macaques are principal ...

, which are nonhuman primates, are known to have extended their northern range into

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the n ...

by making use of hot springs to protect themselves from cold stress. Hot spring baths (''

onsen In Japan, are the country's hot springs and the bathing facilities and traditional inns around them. As a volcanically active country, Japan has many onsens scattered throughout all of its major islands. There are approximately 25,000 hot ...

'') have been in use in Japan for at least two thousand years, traditionally for cleanliness and relaxation, but increasingly for their therapeutic value. In the Homeric Age of Greece (ca. 1000 BCE), baths were primarily for hygiene, but by the time of

Hippocrates Hippocrates of Kos (; grc-gre, Ἱπποκράτης ὁ Κῷος, Hippokrátēs ho Kôios; ), also known as Hippocrates II, was a Greek physician of the classical period who is considered one of the most outstanding figures in the history o ...

(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.

Therapeutic uses

Because of both the

folklore Folklore is shared by a particular group of people; it encompasses the traditions common to that culture, subculture or group. This includes oral traditions such as tales, legends, proverbs and jokes. They include material culture, rangin ...

and the claimed

medical Medicine is the science and practice of caring for a patient, managing the diagnosis, prognosis, prevention, treatment, palliation of their injury or disease, and promoting their health. Medicine encompasses a variety of health care practic ...

value attributed to some hot springs, they are often popular

tourist Tourism is travel for pleasure or business; also the theory and practice of touring, the business of attracting, accommodating, and entertaining tourists, and the business of operating tours. The World Tourism Organization defines tourism ...

destinations, and locations for

rehabilitation Rehabilitation or Rehab may refer to: Health * Rehabilitation (neuropsychology), therapy to regain or improve neurocognitive function that has been lost or diminished * Rehabilitation (wildlife), treatment of injured wildlife so they can be retur ...

clinic A clinic (or outpatient clinic or ambulatory care clinic) is a health facility that is primarily focused on the care of outpatients. Clinics can be privately operated or publicly managed and funded. They typically cover the primary care needs ...

s for those with

disabilities Disability is the experience of any condition that makes it more difficult for a person to do certain activities or have equitable access within a given society. Disabilities may be cognitive, developmental, intellectual, mental, physical, ...

. However, the scientific basis for therapeutic bathing in hot springs is uncertain. Hot bath therapy for

lead poisoning Lead poisoning, also known as plumbism and saturnism, is a type of metal poisoning caused by lead in the body. The brain is the most sensitive. Symptoms may include abdominal pain, constipation, headaches, irritability, memory problems, infertil ...

was common and reportedly highly successful in the 18th and 19th centuries, and may have been due to

diuresis Diuresis () is increased urination (polyuria) or, in the related word senses more often intended, the physiological process that produces such an increase or the administration of medications to encourage that process. It involves extra urine pr ...

(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 with

rheumatoid arthritis Rheumatoid arthritis (RA) is a long-term autoimmune disorder that primarily affects joints. It typically results in warm, swollen, and painful joints. Pain and stiffness often worsen following rest. Most commonly, the wrist and hands are inv ...

and

ankylosing spondylitis Ankylosing spondylitis (AS) is a type of arthritis characterized by long-term inflammation of the joints of the spine typically where the spine joins the pelvis. Occasionally areas affected may include other joints such as the shoulders or hi ...

have been reported in studies of spa therapy, but these studies have methodological problems, such as the obvious impracticality of placebo-controlled studies (in which a patient does not know if they are receiving the therapy). As a result, the therapeutic effectiveness of hot spring therapy remains uncertain.

Precautions

Hot springs in volcanic areas are often at or near the

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 env ...

. People have been seriously scalded and even killed by accidentally or intentionally entering these springs. Some hot springs microbiota are infectious to humans: * ''

Naegleria fowleri ''Naegleria fowleri'', colloquially known as a "brain-eating amoeba", is a species of the genus ''Naegleria'', belonging to the phylum Percolozoa, which is technically not classified as true amoeba, but a shapeshifting amoeboflagellate excava ...

'', an excavate

amoeba An amoeba (; less commonly spelled ameba or amœba; plural ''am(o)ebas'' or ''am(o)ebae'' ), often called an amoeboid, is a type of cell or unicellular organism with the ability to alter its shape, primarily by extending and retracting pseudop ...

, lives in warm unsalted waters worldwide and causes a fatal

meningitis Meningitis is acute or chronic inflammation of the protective membranes covering the brain and spinal cord, collectively called the meninges. The most common symptoms are fever, headache, and neck stiffness. Other symptoms include confusion or ...

should the organisms enter the nose. * ''

Acanthamoeba ''Acanthamoeba'' is a genus of amoebae that are commonly recovered from soil, fresh water, and other habitats. ''Acanthamoeba'' has two evolutive forms, the metabolically active trophozoite and a dormant, stress-resistant cyst. Trophozoites are ...

'' also can spread through hot springs, according to the US

Centers for Disease Control The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georgi ...

- The organisms enter through the eyes or via an open wound. * ''

Legionella ''Legionella'' is a genus of pathogenic gram-negative bacteria that includes the species '' L. pneumophila'', causing legionellosis (all illnesses caused by ''Legionella'') including a pneumonia-type illness called Legionnaires' disease and a mil ...

have been spread through hot springs. *''

Neisseria gonorrhoeae ''Neisseria gonorrhoeae'', also known as ''gonococcus'' (singular), or ''gonococci'' (plural), is a species of Gram-negative diplococci bacteria isolated by Albert Neisser in 1879. It causes the sexually transmitted genitourinary infection gon ...

'' was reported to have very likely been acquired from bathing in a hot spring according to one

case study A case study is an in-depth, detailed examination of a particular case (or cases) within a real-world context. For example, case studies in medicine may focus on an individual patient or ailment; case studies in business might cover a particular fi ...

, with the near-body temperature, slightly acidic, isotonic, organic matter-containing waters thought to facilitate the survival of the pathogen.

Etiquette

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). 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. In some countries, if it is a public hot spring, swimwear is required.

Examples

There are hot springs in many places and on all continents of the world. Countries that are renowned for their hot springs include

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...

Costa Rica Costa Rica (, ; ; literally "Rich Coast"), officially the Republic of Costa Rica ( es, República de Costa Rica), is a country in the Central American region of North America, bordered by Nicaragua to the north, the Caribbean Sea to the no ...

Iran Iran, officially the Islamic Republic of Iran, and also called Persia, is a country located in Western Asia. It is bordered by Iraq and Turkey to the west, by Azerbaijan and Armenia to the northwest, by the Caspian Sea and Turkmeni ...

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 ...

Peru , image_flag = Flag of Peru.svg , image_coat = Escudo nacional del Perú.svg , other_symbol = Great Seal of the State , other_symbol_type = National seal , national_motto = "Firm and Happy f ...

Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia, at the junction of the East and South China Seas in the northwestern Pacific Ocean, with the People's Republic of China (PRC) to the northwest, Japan to the no ...

Turkey Turkey ( tr, Türkiye ), officially the Republic of Türkiye ( tr, Türkiye Cumhuriyeti, links=no ), is a transcontinental country located mainly on the Anatolian Peninsula in Western Asia, with a small portion on the Balkan Peninsula ...

, and the

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., ...

, but there are hot springs in many other places as well: * Widely renowned since a chemistry professor's report in 1918 classified them as one of the world's most electrolytic mineral waters, the Rio Hondo Hot Springs in northern

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the List of South American countries by area, second-largest ...

have become among the most visited on earth. The

Cacheuta Spa The Cacheuta Spa ( es, Termas de Cacheuta, ) is a bathing establishment in Argentina exploiting the natural hot springs at Cacheuta on the Mendoza River in the foothills of the Andes.Chaudes-Aigues Chaudes-Aigues (; oc, Chaudas Aigas, ) is a commune in the Cantal department in south-central France. It is a spa town, famous for its hot spring waters. Geography The commune is situated in the Massif Central in Aubrac. Its inhabitants are ...

. Located at the heart of the French volcanic region

Auvergne Auvergne (; ; oc, label= Occitan, Auvèrnhe or ) is a former administrative region in central France, comprising the four departments of Allier, Puy-de-Dôme, Cantal and Haute-Loire. Since 1 January 2016, it has been part of the new region Au ...

, the thirty natural hot springs of Chaudes-Aigues have temperatures ranging from to more than . The hottest one, the "Source du Par", has a temperature of . The hot waters running under the village have provided heat for the houses and for the church since the 14th Century. Chaudes-Aigues (Cantal, France) is a

spa town A spa town is a resort town based on a mineral spa (a developed mineral spring). Patrons visit spas to "take the waters" for their purported health benefits. Thomas Guidott set up a medical practice in the English town of Bath, Somerset, B ...

known since the Roman Empire for the treatment of rheumatism. * Carbonate aquifers in foreland tectonic settings can host important thermal springs although located in areas commonly not characterised by regional high heat flow values. In these cases, when thermal springs are located close or along the coastlines, the subaerial and/or submarine thermal springs constitute the outflow of marine groundwater, flowing through localised fractures and karstic rock-volumes. This is the case of springs occurring along the south-easternmost portion of the Apulia region (Southern Italy) where few sulphurous and warm waters () outflow in partially submerged caves located along the Adriatic coast, thus supplying the historical spas of Santa Cesarea Terme. These springs are known from ancient times (Aristotele in III Century BC) and the physical-chemical features of their thermal waters resulted to be partly influenced by the sea level variations. * One of the potential geothermal energy reservoirs in India is the Tattapani thermal springs of Madhya Pradesh. * The silica-rich deposits found in Nili Patera, the

volcanic 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 plat ...

caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcano eruption. When large volumes of magma are erupted over a short time, structural support for the rock above the magma chamber is ...

in Syrtis Major,

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...

, are thought to be the remains of an extinct hot spring system.

References

External links

Thermal Springs List for the United States
��1,661 hot springs *
A scholarly paper with a map of over 20 geothermal areas in Uganda

List of 100 thermal hot springs and hot pools in New Zealand

{{Authority control Bathing Springs (hydrology) Bodies of water Geothermal areas