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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 heli ...
produced by the emergence of geothermally heated
groundwater Groundwater is the water Water (chemical formula H2O) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...

groundwater
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 s are formed. Magma is found beneath the surface of the , and evidence of has also been discovered on other and some s. Besides molten rock, magma may also contain suspended ...

magma
(molten rock) or by circulation through faults to hot rock deep in the
Earth's crust 350px, Plates in the crust of Earth Earth's crust is a thin shell on the outside of Earth, accounting for less than 1% of Earth's volume. It is the top component of the lithosphere, a division of Earth's layers that includes the Crust (geology), ...
. 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 conside ...

radioactive decay
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 Earth's outer core is a fluid layer about thick and composed of mostly iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt ...
, 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
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 one ...

silica
, to bicarbonate springs saturated with
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is ...

carbon dioxide
and
carbonate minerals Carbonate minerals are those minerals containing the carbonate ion, CO32−. Carbonate divisions Anhydrous carbonates *Calcite group: trigonal **Calcite CaCO3 **Gaspeite (Ni,Mg,Fe2+)CO3 **Magnesite MgCO3 **Otavite CdCO3 **Rhodochrosite MnCO3 **S ...
. 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 In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the ...
, 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 Temperature is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy, present in all matter, which is the source of th ...
(normally about ) provides a critical discussion of the definition of a hot spring. * 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 (NOAA ) is an American scientific and regulatory agency within the United States Department of Commerce The United States Department of Commerce is an executive department The United ...

NOAA
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 Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these ...

heat
produced from the
Earth's mantle Earth's mantle is a layer of silicate rock between the crust and the outer core Earth's outer core is a fluid layer about thick and composed of mostly iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt ...
. This takes place in two ways. In areas of high volcanic activity,
magma Magma () is the molten or semi-molten natural material from which all s are formed. Magma is found beneath the surface of the , and evidence of has also been discovered on other and some s. Besides molten rock, magma may also contain suspended ...

magma
(molten rock) may be present at shallow depths in the
Earth's crust 350px, Plates in the crust of Earth Earth's crust is a thin shell on the outside of Earth, accounting for less than 1% of Earth's volume. It is the top component of the lithosphere, a division of Earth's layers that includes the Crust (geology), ...
. 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 Earth is the third planet from the Sun and the only astronomical object known to harbor life. About 29% of Earth's surface is land consi ...
. 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 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 1.251 years. It makes up 0.012% (120 parts-per notation, ppm) of the total amount of potassium found in nature. Potassium-40 is a rare example of an isotope th ...

potassium-40
,
uranium-238 Uranium-238 (238U or U-238) is the most common isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons A proton is a subatomic particle, symbol or , with a positive electric charge Electric ...
,
uranium-235 Uranium-235 (235U) is an Isotopes of uranium, 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 th ...

uranium-235
, and
thorium-232 Thorium Thorium is a weakly radioactive decay, radioactive metallic chemical element with the Symbol (chemistry), symbol Th and atomic number 90. Thorium is silvery and tarnishes black when it is exposed to air, forming thorium dioxide; it is mo ...

thorium-232
. In areas with no volcanic activity, this heat flows through the crust by a slow process of
thermal conduction Thermal conduction is the transfer of by microscopic collisions of particles and movement of electrons within a body. The colliding particles, which include molecules, atoms and electrons, transfer disorganized microscopic kinetic and potential en ...

thermal conduction
, but in volcanic areas, the heat is carried to the surface more rapidly by bodies of magma. A hot spring that periodically jets water and steam is called a
geyser A geyser (, ) 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 ...

geyser
. In active volcanic zones such as
Yellowstone National Park Yellowstone National Park is an American national park#REDIRECT National park A national park is a park in use for Conservation (ethic), conservation purposes, created and protected by national governments. Often it is a reserve of natur ...

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 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 water Water (chemical formula H2O) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organism ...

steam
, the result is a
fumarole __NOTOC__ Sampling gases at a fumarole on Washington Washington commonly refers to: * Washington (state), United States * Washington, D.C., the capital of the United States ** Federal government of the United States (metonym) ** Washington metr ...

fumarole
. If the water is mixed with mud and
clay Clay is a type of fine-grained natural soil File:Stagnogley.JPG, Surface-water-Gley soil, gley developed in glacial till, Northern Ireland. Soil is a mixture of organic matter, minerals, gases, liquids, and organisms that together support ...

clay
, the result is a
mud pot Mud is soil File:Stagnogley.JPG, Surface-water-Gley soil, gley developed in glacial till, Northern Ireland. Soil is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Earth's body of soil, called ...
. 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, the family of Martha Bulloch Roosevelt), first came ...
(frequented for its
therapeutic A therapy or medical treatment (often abbreviated tx, Tx, or Tx) is the attempted remediation of a health Health is a state of physical, mental and social well-being Well-being, also known as ''wellness'', ''prudential value'' or ''quality ...

therapeutic
effects by
paraplegic Paraplegia is an impairment in Motor control, motor or Sensory nervous system, 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 th ...
U.S. President The president of the United States (POTUS) is the head of state A head of state (or chief of state) is the public persona who officially embodies a state (polity), state#Foakes, Foakes, pp. 110–11 " he head of statebeing an embodime ...

U.S. President
Franklin D. Roosevelt Franklin Delano Roosevelt (, ; January 30, 1882April 12, 1945), often referred to by his initials FDR, was an American politician who served as the 32nd president of the United States from 1933 until his death in 1945. A member of the De ...
, who built the
Little White House The Little White House was the personal retreat of Franklin D. Roosevelt, the List of Presidents of the United States, 32nd President of the United States, located in the Warm Springs Historic District, Historic District of Warm Springs, Georgia, W ...

Little White House
there). Here the groundwater originates as rain and snow (
meteoric waterMeteoric water is the water derived from Precipitation (meteorology), 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 fro ...
) 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 secondary m ...
( Hollis Quartzite) to a depth of and is heated by the normal geothermal gradient.


Chemistry

Because heated water can hold more
solid Solid is one of the four fundamental states of matter (the others being liquid A liquid is a nearly incompressible fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) under an applied ...

solid
s than cold water, the water that issues from hot springs often has a very high
mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology), rocks of which it is composed, and the proces ...

mineral
content, containing everything from
calcium Calcium is a with the Ca and 20. As an , calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to its heavier homologues and . It is the fifth most abun ...

calcium
to
lithium Lithium (from el, λίθος, lithos, lit=stone) is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consist ...

lithium
and even
radium Radium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science tha ...

radium
. 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 An ion () is a particle In the Outline of physical science, physical sciences, a particle (or corpuscule in older texts) is a small wikt:local, localized physical body, object to which can be ascribed several physical ...

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

silica
(). The solubility of silica depends strongly upon temperature, so upon cooling, the silica is deposited as
geyserite Geyserite from Iceland Geyserite is a form of opal Opal is a hydrated amorphous form of Silicon dioxide, silica (SiO2·''n''H2O); its water content may range from 3 to 21% by weight, but is usually between 6 and 10%. Because of its amorph ...

geyserite
, a form of
opal Opal is a hydrate In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, comp ...

opal
(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 A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by ...

hydrogen sulfide
(), which is oxidized to form
sulfuric acid Sulfuric acid ( and the ) or sulphuric acid (), known in antiquity as oil of vitriol, is a composed of the elements , and , with the . It is a colorless, odorless and liquid that is with water. Pure sulfuric acid does not exist naturally ...

sulfuric acid
, . 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 , sometimes with variable amounts of , , s, s, and other s found on or near some s. Clay minerals form in the presence of water and have been important to life, and many theories of involve them. They are important constitu ...
s,
oxide minerals The oxide mineral class includes those 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 ...
, and a residue of silica. Bicarbonate hot springs are fed by hydrothermal fluids that form when
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is ...

carbon dioxide
() and groundwater react with
carbonate rocks 250px, Carbonate ooids on the surface of a limestone; Carmel Formation">limestone.html" ;"title="ooids on the surface of a limestone">ooids on the surface of a limestone; Carmel Formation (Middle Jurassic) of southern Utah, USA. Largest is 1.0 mm ...
. 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. Travertine often has a fibrous or concentric appearance and exists in white, tan, cream-colored, and even rusty varieties. It is formed by ...

travertine
, 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
geyser A geyser (, ) 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 ...

geyser
, or
fountain A fountain, from the "fons" ( "fontis"), meaning source or , is a decorative reservoir for discharging into a basin to supply . It is also a structure that jets water into the air for a decorative or dramatic effect. Fountains were original ...

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: * The
Dalhousie Springs Dalhousie Springs, also known as Witjira-Dalhousie Springs, is a group of over 60 natural artesian springs located in Witjira National Park on the western fringe of the Simpson Desert, 180 kilometres northeast of Oodnadatta, South Australia, Oodna ...

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. * The 2,850 hot springs of
Beppu is a Cities of Japan, city in Ōita Prefecture on the island of Kyushu, Japan, at the west end of Beppu Bay. As of March 31, 2017, the city had a population of 122,643
in Japan are the highest flow hot spring complex in Japan. Together the Beppu hot springs produce about 1,592 liters/second, or corresponding to an average hot spring flow of 0.56 liters/second. * The 303 hot springs of Kokonoe in Japan produce 1,028 liters/second, which gives the average hot spring a flow of 3.39 liters/second. *
Ōita Prefecture is a Prefectures of Japan, 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 Square kilometre, km² (2,448 sq mi). Ōita Prefecture borders Fuk ...
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 in
Akita Prefecture is a prefecture A prefecture (from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Th ...
, 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 8.5 million square kilometers (3.2 million square miles) and with over 211 mill ...

Brazil
's ("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 ** Portug ...

Portuguese
) 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 located in the region of the . Florida is bordered to the west by the , to the northwest by , to the north by , to the east by and , and to the south by the and ; it is the only state that borders both the Gulf of Mexico and ...

Florida
, there are 33 recognized "magnitude one
springs 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 heli ...
" (having a flow in excess of .
Silver Springs, Florida Silver Springs is an unincorporated community File:Entering Heinola, Minnesota.jpg, Sign at Heinola, Minnesota, Heinola, an unincorporated community in Otter Tail County, Minnesota An unincorporated area is a region not governed by a local mu ...
has a flow of more than . * The Excelsior Geyser Crater in
Yellowstone National Park Yellowstone National Park is an American national park#REDIRECT National park A national park is a park in use for Conservation (ethic), conservation purposes, created and protected by national governments. Often it is a reserve of natur ...

Yellowstone National Park
yields about . * Evans Plunge in
Hot Springs, South Dakota Hot Springs (LakotaLakota may refer to: * Lakota people, a confederation of seven related Native American tribes *Lakota language Lakota (), also referred to as Lakhota, Teton or Teton Sioux, is a Siouan language spoken by the Lakota people o ...
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 it, Toscano (man) it, Toscana (woman) , population_note = , population_blank1_title = , population_blank1 = , demographics_type1 = Citizenship , demographics1_footnotes = , demog ...
, Italy with around 500 liters a second * Lava Hot Springs in
Idaho Idaho () is a in the region of the United States. It borders the state of to the east and northeast, to the east, and to the south, and and to the west. To the north, it shares a small portion of the with the province of . With a po ...

Idaho
has a flow of 130 liters/second. * in
Colorado Colorado (, other variants) is a state in the Mountain states, 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 weste ...

Colorado
has a flow of 143 liters/second. * Elizabeth Springs in western
Queensland Queensland ( ) is a state situated in northeastern Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the ...

Queensland
, 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 in
Iceland Iceland ( is, Ísland; ) is a Nordic Nordic most commonly refers to: * Nordic countries, written in plural as Nordics, the northwestern European countries, including Scandinavia, Fennoscandia and the List of islands in the Atlantic Ocean#N ...

Iceland
has a flow of 180 liters/second. * There are at least three hot springs in the
Nage The Nage are an indigenous people living on the eastern Indonesia Indonesia ( ), officially the Republic of Indonesia ( id, Republik Indonesia, links=yes ), is a country in Southeast Asia and Oceania between the Indian Ocean, Indian and P ...
region south west of
Bajawa Bajawa is a town of Flores Flores island () is one of the Lesser Sunda Islands The Lesser Sunda Islands ( id, Kepulauan Nusa Tenggara "southeastern archipelago" or "lesser sunda archipelago") are an archipelago An archipelago ...

Bajawa
in
Indonesia Indonesia ( ), officially the Republic of Indonesia ( id, Republik Indonesia, links=yes ), is a country in Southeast Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia or SEA, is t ...

Indonesia
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,
Indonesia Indonesia ( ), officially the Republic of Indonesia ( id, Republik Indonesia, links=yes ), is a country in Southeast Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia or SEA, is t ...

Indonesia
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.


Hot spring ecosystems

Hot springs often host communities of microorganisms adapted to life in hot, mineral-laden water. These include
thermophile 300px, Thermophiles produce some of the bright colors of Grand Prismatic Spring, Yellowstone National Park ">Yellowstone_National_Park.html" ;"title="Grand Prismatic Spring, Yellowstone National Park">Grand Prismatic Spring, Yellowstone National P ...
s, which are a type of
extremophile An extremophile (from Latin ' meaning "extreme" and Greek ' () meaning "love") is an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the ...
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 (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typ ...

bacteria
, such as ''
Aquifex ''Aquifex'' is a bacterial Bacteria (; common noun bacteria, singular bacterium) are a type of biological cell. They constitute a large domain of prokaryotic microorganism A microorganism, or microbe,, ''mikros'', "small") and ''or ...
'' and other
Aquificales The Aquificae phylum (biology), phylum is a diverse collection of bacteria that live in harsh environmental settings. The name 'Aquificae' was given to this phylum based on an early genus identified within this group, ''Aquifex'' (“water maker ...
, 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 of that obtain energy via . The name ''cyanobacteria'' refers to their color (), giving them their other name, "blue-green algae", though modern botanists restrict the term ' to s and do not ...

cyanobacteria
, such as '' Spirulina'', ''
Oscillatoria ''Oscillatoria'' is a genus of filamentous The word filament, which is descended from Latin ''filum'' meaning "Thread (yarn), thread", is used in English for a variety of thread-like structures, including: In commerce * Fiber or, more loosely ...

Oscillatoria
'', and ''
Synechococcus ''Synechococcus'' (from the Greek ''synechos'', in succession, and the Greek ''kokkos'', granule) is a unicellular cyanobacterium Cyanobacteria , also known as Cyanophyta, are a phylum In biology, a phylum (; plural The plural (somet ...
'', and
green sulfur bacteria The green sulfur bacteria (Chlorobiaceae) are a family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose of families is to maintain the well-being ...
such as ''
Chloroflexus Chloroflexales is one of two orders of bacteria in the class Chloroflexi (class), Chloroflexi. See also * List of bacterial orders References External links

Phototrophic bacteria Chloroflexi (phylum) {{bacteria-stub ...
''. These organisms are all capable of
photosynthesis Photosynthesis is a process used by plants and other organisms to convert Conversion or convert may refer to: Arts, entertainment, and media * Conversion (Doctor Who audio), "Conversion" (''Doctor Who'' audio), an episode of the audio drama ' ...

photosynthesis
, though green sulfur bacteria produce
sulfur Sulfur (in nontechnical British English: sulphur) is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: th ...

sulfur
rather than
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
during photosynthesis. Still further from the vent, where temperatures drop below , conditions are favorable for a complex community of microorganisms that includes ''Spirulina'', ''
Calothrix ''Calothrix'' is a genus of cyanobacteria. They are generally found in freshwater. References

Rivulariaceae Cyanobacteria genera {{cyanobacteria-stub ...
'',
diatoms Diatoms (''diá-tom-os'' 'cut in half', from ''diá'', 'through' or 'apart', and the root of ''tém-n-ō'', 'I cut') are a major group of algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic ...

diatoms
and other single-celled
eukaryotes Eukaryotes () are organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, properties of life. It is a synonym for "Outline ...
, 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 ) constitute a domain Domain may refer to: Mathematics *Domain of a function, the set of input values for which the (total) function is defined **Domain of definition of a partial function **Natural domain of a pa ...

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 Cyanidiophyceae is a class of unicellular red algae Red algae, or Rhodophyta ( , ; ), are one of the oldest groups of eukaryotic algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic Photosy ...
), fungi, and diatoms. Iron-rich hot springs contain communities of photosynthetic organisms that oxidize reduced (ferrous) iron to oxidized (ferric) iron. Hot springs are a dependable source of water that provides a rich chemical environment. This includes Oxidation, 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.


Human uses

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


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 physical therapy, rehabilitation clinics for those with disabilities. 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 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. 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'', an excavata, excavate amoeba, lives in warm unsalted waters worldwide and causes a fatal meningitis should the organisms enter the nose. * ''Acanthamoeba'' also can spread through hot springs, according to the US Centers for Disease Control - The organisms enter through the eyes or via an open wound. * ''Legionella''
bacteria Bacteria (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typ ...

bacteria
have been spread through hot springs. *''Neisseria gonorrhoeae'' was reported to have very likely been acquired from bathing in a hot spring according to one case study, with the near-body temperature, slightly acidic, Isotonic fluid, 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, Costa Rica,
Iceland Iceland ( is, Ísland; ) is a Nordic Nordic most commonly refers to: * Nordic countries, written in plural as Nordics, the northwestern European countries, including Scandinavia, Fennoscandia and the List of islands in the Atlantic Ocean#N ...

Iceland
, Iran, Onsen, Japan, New Zealand,
Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At 8.5 million square kilometers (3.2 million square miles) and with over 211 mill ...

Brazil
, Peru, Taiwan, Turkey, and the United States, 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 Termas de Rio Hondo, Rio Hondo Hot Springs in northern Argentina have become among the most visited on earth. The Cacheuta Spa is another famous hot springs in Argentina. * The springs in Europe with the highest temperatures are located in France, in a small village named Chaudes-Aigues. Located at the heart of the French volcanic region Auvergne, 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 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 Volcano, volcanic caldera in Syrtis Major Planum, Syrtis Major, Mars, are thought to be the remains of an extinct hot spring system.


See also

* Hotspot (geology) * Hydrothermal vents * Earliest known life forms * List of spa towns * Mineral spring * Valley of the Geysers


References


Further reading

* * * *


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 Hot springs, Bathing Springs (hydrology) Bodies of water Geothermal areas