A rocky surface with a mound centrally in the image. The mound has holes in the top. Surrounding rocks have been stained orange and yellow. There is smoke or steam rising from the top.
A fumarole in the Solfatra crater, the orange and yellow colouration is from minerals that are deposited by the superheated fumes as they cool to ambient temperature.
A green landscape with a platform of grey rock. steam is rising from a pool or hole in the middle of the platform
Geysir, a geyser in Iceland, after which the phenomenon is named.[1]

Geothermal activity is a group of natural heat transfer processes, occurring on Earth's surface, caused by the presence of excess heat in the subsurface of the affected area, usually caused by the presence of an igneous intrusion underground.[2] Geothermal activity can manifest itself in a variety of different phenomena, including, among others, elevated surface temperatures, various forms of hydrothermal activity, and the presence of fumaroles that emit hot volcanic gases.

Background physics

Main article: Earth's internal heat budget

Geothermal activity mostly appears in volcanic provinces, where it is fueled by the presence of a magma chamber. In some rare cases it can be caused by underground fires or by large deposits of radioactive elements. Other sources of internal heating can be gravitational differentiation of substances, tidal friction, metamorphism, or phase transitions. The release of heat to the surface occurs either in the form of a conductive heat flow, or in the form of convective heat transfer by groundwater or gases.[3]

A pool of greyish-blue bubbling sludge surrounded by rocks and steam
Mud pots in the Sol de Mañana Hydrothermal field, Bolivia.

Types of geothermal activity

Fumaroles and vents

Fumaroles, or volcanic vents, are holes in the ground from which volcanic vapors and gases escape to the atmosphere. Geothermally active areas are often located over an active magma chamber, which constantly releases hot gases that travel to the surface through cavities in the rock. Where these cavities reach the surface they form fumaroles. Areas where these vents are concentrated are known as Fumarole fields. Fumaroles tend to form concentrated deposits of sulfuric minerals, which fall out of suspension when the volcanic gases cool to the air.[4]

Ice cauldrons

Ice cauldrons are a feature that occurs when an ice cap is affected by geothermal heating, either from active volcanism or the continuous heat production from an active geothermal area. Ice cauldrons can have many different appearances. These range from a smooth dent in the ice cap to deep holes with very steep walls formed by concentric rings of crevasses. The width of ice cauldrons can range from 50 meters up to around 10 kilometers, while depth can range from several meters to hundreds of meters. The shape of the cauldron can be stable or highly variable, and is not related to the nature of the underlaying heat source.[5]

Hydrothermal activity

Geothermal heat and groundwater can interact in several ways.


Geysers are the most well known hydrothermal feature. they occur when groundwater in underground cavities becomes superheated under a lid of colder surface water. When the superheated water breaches the surface, it flashes to steam, causing the pressure below it to suddenly drop, which causes a chain reaction where most of the water in the geyser's feed system flashes to steam all at once.

There are two main types of geyser. Fountain geysers, which erupt in violent bursts from a pool, and cone geysers, which erupt in steady jets for minutes at a time from a sinter cone of siliceous material that has been deposited surrounding the main vent. [6]

Hot springs and mud pots

A crystal-clear pool with a bright yellow bottom. Where the water is deeper the bottom seems more green or blue. In the background, where the water of the first pool turns red, there is a raised rim surrounding a smaller bright-blue pool, which steams heavily. The pools have white beaches and are surrounded by a pine forest
Two Hot springs in Waiotapu, New Zealand, with Artist's Palette in the foreground, and Champagne Pool directly behind it in the background.

In other areas, the heated groundwater gathers in pools, forming hot springs.[7] Where very little groundwater is available, rising hot groundwater in combination with microbial activity leads to the formation of mud pots.[8] The behaviour of these mud pots can vary on a seasonal cycle based on variations in the amount of rainfall and the level of the water table. [9][10]

Hydrothermal explosions

Hydrothermal explosions occur when a mass of superheated water is unable to reach the surface, causing pressure underground to rise until a critical point is reached and an explosion occurs, ejecting the superheated water along with the rock. [11]

See also


  1. ^ "geyser | Etymology, origin and meaning of geyser by etymonline". www.etymonline.com. Retrieved 2023-03-23.
  2. ^ "Лаборатория тепломассопереноса // Геологический институт РАН". geotherm.ginras.ru (in Russian). Retrieved 2023-03-22.
  3. ^ "Геотермальная активность // ГОСТ 19431-84 ГОСТ 21027-75 ГОСТ 32144-2013 ГОСТ 24291-90 ГОСТ Р 57114-2016 ГОСТ 19880-74". www.panpwr.ru (in Russian). Retrieved 2023-03-22.
  4. ^ Philpotts, Anthony R. (2009). Principles of igneous and metamorphic petrology. Jay J. Ague (2nd ed.). Cambridge, UK: Cambridge University Press. ISBN 978-0-521-88006-0. OCLC 231581100.
  5. ^ Gudmundsson, Magnús T. (2015), "Ice Cauldron", in Hargitai, Henrik; Kereszturi, Ákos (eds.), Encyclopedia of Planetary Landforms, New York, NY: Springer, pp. 953–958, doi:10.1007/978-1-4614-3134-3_192, ISBN 978-1-4614-3134-3, retrieved 2023-04-24
  6. ^ "Hydrothermal Features - Yellowstone National Park". www.nps.gov. National Park Service. Retrieved 2023-04-02.
  7. ^ O'Banion, K.; Hall, C. (1980-07-14). "Geothermal energy and the land resource: conflicts and constraints in The Geysers-Calistoga KGRA". doi:10.2172/6817678. OSTI 6817678. S2CID 129626036. ((cite journal)): Cite journal requires |journal= (help)
  8. ^ Dahlquist, G. R.; Cox, A. D. (2016-12-01). "What's in the mud?: Water-rock-microbe interactions in thermal mudpots and springs". AGU Fall Meeting Abstracts. 2016: B21E–0469. Bibcode:2016AGUFM.B21E0469D.
  9. ^ "Mudpots - Old Faithful Virtual Visitor Center". www.nps.gov. Retrieved 2023-04-21.
  10. ^ Lynch, D. K.; Hudnut, K. W. (2008-08-01). "The Wister Mud Pot Lineament: Southeastward Extension or Abandoned Strand of the San Andreas Fault?". Bulletin of the Seismological Society of America. 98 (4): 1720–1729. Bibcode:2008BuSSA..98.1720L. doi:10.1785/0120070252. ISSN 0037-1106.
  11. ^ "Hydrothermal Explosions | U.S. Geological Survey". www.usgs.gov. Retrieved 2023-07-18.