a type of thermal spring in which hot water is brought to the surface. The water temperature of a hot spring is usually 6.5 °C (12 °F) or more above mean air temperature. Note that by this definition, "thermal spring" is not synonymous with the term "hot spring"
a spring whose hot water is brought to the surface (synonymous with a thermal spring). The water temperature of the spring is usually 8.3 °C (15 °F) or more above the mean air temperature.
a spring with water above the core human body temperature – 36.7 °C (98 °F).
a spring with water above average ambient ground temperature, a definition favored by some
a spring with water temperatures above 50 °C (122 °F)
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 Geophysical Data Center defines a "warm spring" as a spring with water between 20 and 50 °C (68 and 122 °F).
Sources of heat
The water issuing from a hot spring is heated by geothermal heat, i.e., heat from the Earth's mantle. In general, the temperature of rocks within the earth increases with depth. The rate of temperature increase with depth is known as the geothermal gradient. If water percolates deeply enough into the crust, it will be heated as it comes into contact with hot rocks. The water from hot springs in non-volcanic areas is heated in this manner.
In active volcanic zones such as Yellowstone National Park, water may be heated by coming into contact with magma (molten rock). The high temperature gradient near magma may cause water to be heated enough that it boils or becomes superheated. If the water becomes so hot that it builds steam pressure and erupts in a jet above the surface of the Earth, it is called a geyser. If the water only reaches the surface in the form of steam, it is called a fumarole. If the water is mixed with mud and clay, it is called a mud pot.
Note that hot springs in volcanic areas are often at or near the boiling point. People have been seriously burned and even killed by accidentally or intentionally entering these springs.
Hot springs range in flow rate from the tiniest "seeps" to veritable rivers of hot water. Sometimes there is enough pressure that the water shoots upward in a geyser, or fountain.
High flow hot springs
There are many claims in the literature about the flow rates of hot springs. It should be noted that there are many more very high flow non-thermal springs than geothermal springs. For example, there are 33 recognized "magnitude one springs" (having a flow in excess of 2,800 liters/second) in Florida alone. Silver Springs, Florida has a flow of more than 21,000 liters/second. Springs with high flow rates include:
Evans Plunge in Hot Springs, South Dakota has a flow rate of 5,000 gallons-per-minute of 87 degree spring water. The Plunge, built in 1890, is the world's largest natural warm water indoor swimming pool.
The hot springs of Brazil's Caldas Novas ("New Hot Springs" in 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.
The 2,850 hot springs of Beppu 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.
The Oita Prefecture 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, which has a flow rate of 150 liters/second. The Tamagawa Hot Spring feeds a 3 m (9.8 ft) wide stream with a temperature of 98 °C (208 °F).
There are at least three hot springs in the Nage region 8 km (5.0 mi) south west of Bajawa in Indonesia that collectively produce more than 453.6 liters/second.
There are another three large hot springs (Mengeruda, Wae Bana and Piga) 18 km (11 mi) north east of Bajawa, Indonesia that together produce more than 450 liters/second of hot water.
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.
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 385 litres (86 gallons) per minute and 47º Celsius (118º Fahrenheit) year-round.
A thermophile is an organism — a type of extremophile — that thrives at relatively high temperatures, between 45 and 80 °C (113 and 176 °F). Thermophiles are found in hot springs, as well as deep seahydrothermal vents and decaying plant matter such as peat bogs and compost.
Viruses have been collected from very extreme environments, for example, a hot spring with a temperature of 87 to 93 °C (189 to 199 °F) and an incredibly acidic pH of 1.5 in Pozzuoli, Italy. These viruses were observed to infect cells in the laboratory.
Rincon de la Vieja National Park in Guanacaste, Costa Rica, is a famous area for different types of springs, Hot Springs, Sulfur Springs and Volcanic Mud Springs Rincon de la Vieja Volcano National Park.
The town of Spa, Belgium is the origin of the word "spa" and features springs with water temperatures of 32 °C (90 °F). Casanova visited Spa in 1783 looking for business opportunities but was disappointed.
There are more than 275 hot springs registered in Chile including South America's largest hot spring source in Liquiñe.
The Yangbajing hot springs field about 87 km. north of Lhasa in Tibet is several square kilometers in size, and used to supply a large fraction of the electricity of Lhasa. At an altitude between 4,290 and 4,500 m (14,070 and 14,800 ft), this is a strong candidate for the set of highest altitude hot springs on earth.
Taiwan, is ranked among one of the world's top hot spring sites, harboring a great variety of springs, including hot springs, cold springs, mud springs, and seabed hot springs.
Icaria, Greece features a radioactive hot water spring that has been used since the 4th century BC.
The closest town to Machu Picchu in Peru is Machu Picchu Pueblo, which features several hot springs. The local name for Machu Picchu Pueblo is Aguas Calientes.
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 have become among the most visited on earth. The Cacheuta Spa is another famous hot springs in Argentina.
Oymyakon in eastern Siberia is a candidate for the coldest permanently inhabited location in the Northern Hemisphere and another hot springs site. The Yakut language word "oymyakon" means "river doesn't freeze" after the local tributary of the Indigirka River fed by the hot springs which continues to flow year round in this permafrost region.
Being located in the "Pacific Ring of Fire", Japan is in a volcanic region, and is home to many hot springs. The onsen (a Japanese word for "hot spring") plays a notable role in Japanese culture. Visiting an onsen is a quintessential Japanese experience and is a popular tourist activity.
Australia Peninsula Hot Springs are located one and a half hours drive South of Melbourne on the Mornington Peninsula. 47 °C (117 °F) waters flow from 637 meters to the surface and into private baths and pools.
^Don L. Leet (1982). Physical Geology (6th ed.). Englewood Cliffs, NJ: Prentice-Hall. ISBN0-13-669706-2. "A thermal spring is defined as a spring that brings warm or hot water to the surface." Leet states that there are two types of thermal springs; hot springs and warm springs.
^Miyamoto H, Jitsurong S, Shiota R, Maruta K, Yoshida S, Yabuuchi E (1997). "Molecular determination of infection source of a sporadic Legionella pneumonia case associated with a hot spring bath". Microbiol. Immunol.41 (3): 197–202. PMID9130230.
^Eiko Yabauuchi, Kunio Agata (2004). "An outbreak of legionellosis in a new facility of hot spring Bath in Hiuga City". Kansenshogaku zasshi78 (2): 90–8. ISSN0387-5911. PMID15103899.