virtual-geology.info

Definitions Links general by region applications consequences References Case studies Yellowstone Valles, New Mexico Hot stream flowing from the crater area, Mount St Helens. Photo by Roger Suthren

	Geothermal Energy slide show (Geothermal Education Office)

Definitions

units of geothermal heat flow are Joules per square metre per second, Jm^-2s^-1. However, one Joule per second = 1 Watt (W), so that heat flow is usually expressed as Wm^-2, or more conveniently, mWm^-2 (milliwatts per square metre).

• The above metric units replace the heat-flow unit (HFU), which is still in common usage in North American literature
• 1 HFU = 1 cal cm^-2s^-1 (1 calorie per square centimetre per second).
• For conversion purposes, 1 HFU = 41.8 mWm^-2

Heat sources for geothermal energy are:

• Conductive heat from the mantle
• Heat generated in the crust by decay of radioactive isotopes of U, Th and K
• Shallow magma bodies acting as local heat sources

1. non-thermal areas, geothermal gradient 10 to 40 °K km^-1
2. thermal areas semithermal areas, geotherm up to 70 - 80 °K km^-1
3. hyperthermal areas, geotherm many times greater than in non-thermal areas

• recent volcanic activity
• frequent seismic activity
• high level of conductive heat flow
• hot springs, geysers or fumaroles

• heat source - often magmatic, resulting in high geothermal gradient
• bedrock layer - more or less impermeable
• aquifer/reservoir - permeable, fractured, providing heat exchange surface of large surface area
• source of water replenishment (recharge)
• caprock - impermeable seal and thermal insulator (often formed by 'self-sealing' )

Below are just a few of the thousands of links to geothermal energy information on the Web.

General

• Renewable Energy: power beneath our feet (New Scientist)
• What is geothermal?
• Geothermal Energy—Clean Power From the Earth’s Heat
• Energy 101: Geothermal Energy (video, 4 mins)
• U.S. Department of Energy - Geothermal Technologies Site
• Hot Dry Rock Geothermal Energy Technology (Los Alamos National Laboratory)
• International Geothermal Association

Geothermal Exploration

• Remote sensing in exploration for geothermal resources

Online books

• Volcanology and Geothermal Energy

Geothermal resources by region

Iceland

• National Energy Authority of Iceland
• Iceland Geothermal Energy video (United Nations: 5 mins)
• ISOR - Iceland Geosurvey

  Italy

• Lardarello - the first industrial-scale geothermal energy scheme - video (2 mins)

  UK

• Geothermal energy: a renewable low-carbon resource for the UK
• List of geothermal springs in the UK
• The Potential for Geothermal Energy in South West England
• The Roman Baths at Bath
• The hot springs of Bath
• Geothermal Energy (British Geological Survey)
• UK Geothermal potential (pdf - BGS)
• United Downs Deep Geothermal Power Project, Cornwall
• UK Geoenergy Observatory in Glasgow (BGS)

USA

• Geysers Geothermal Field, California
• Geysers Geothermal Field, California (Scientific American article)
• Steamboat Springs power plants, Nevada and other Ormat sites
• US National Parks: Hot Springs/Geothermal
• Yellowstone National Park
• Yellowstone videos & online tours
• Old Faithful & other Yellowstone webcams
• Geothermal Energy in Hawaii
• Great Basin Center for Geothermal Energy, University of Nevada, Reno
  
  

• Mexico

• Mexico Geothermal Energy
• Cerro Prieto field: images
  

  New Zealand

• Wairakei field (pdf)
• NZ Geothermal resources

  Japan

• Japan - The Economist
• Japan - geothermal power plants map

  Chile

• Geothermal energy in Chile
   

Applications of Geothermal Energy

• Turning waste hot water into electricity
• District heating
• Recycling wastewater in a geothermal field
• District heating: Southampton, UK (pdf)
• Ground source heating and cooling (UK Groundwater Forum)
• Geothermal Heat Pumps (Note: ground source heat pumps which are installed close to the earth's surface are actually exploiting solar energy, rather than the earth's internal energy)
  
  

  Therapeutic:

• Hot Springs in Europe
• Spa therapy through the ages (pdf)

Consequences of Geothermal Exploitation

• Environmental impacts of geothermal energy
• Environmental Compatibility of Geothermal Energy (US Department of Energy) (pdf)
• Subsidence around Wairakei geothermal field, New Zealand

Books:

• ------. 1988. Drawing heat from the earth: geothermal energy technology in Britain. Department of Energy, London.
• ------. 1982. Investigation of the geothermal potential of the UK. - A review of data relating to hot dry rock and selection of targets for detailed.... Institute of Geological Sciences, London.
• ARMSTEAD, H.C.H. (ed.). 1973. Geothermal Energy, Review of Research and Development. Unesco.
• ARMSTEAD, H.C.H. 1983. Geothermal Energy. 2nd edition. E & F.N. Spon.
• DICKSON, M.H. and FANELLI. M (eds). 1995. Geothermal energy. Chichester, Wiley.
• DOWNING, R.A. And GRAY, D.A. (Eds.). 1986. Geothermal energy : the potential in the United Kingdom. London, H.M.S.O.
• EDWARDS, L.M., CHILINGAR, G.V., RIEKE, H.H. & FERTL, W.H. (Eds.) 1982. Handbook of Geothermal Energy. Gulf Publishing Company.
• ELDER, J. 1981. Geothermal Systems. Academic Press.
• GALE, I.N. 1984. Investigation of the geothermal potential of the UK. - An assessment of the geothermal resources of the United Kingdom. British Geological Survey, London.
• KELLAWAY, G.A. (Ed.). 1991. Hot Springs of Bath. Investigations of the Thermal Waters of the Avon Valley. Bath City Council.
• RINEHART, John S. 1980. Geysers and geothermal energy. New York, Springer-Verlag.
• RYBACH, L. & MUFFLER, L.J.P. 1981. Geothermal Systems: Principles and Case Histories. John Wiley & Sons.

Periodicals:

• Journal of Volcanology and Geothermal Research.

Videos:

• ------. 1981 The Earth [Videorecording] : structure, composition [and] evolution. [Programme 9] : Geothermal energy. Milton Keynes : Open University. (Science : a second level course).
• ------. 1996, S268 Physical Resources and Environment. [Programme 6] : Renewable Energies. Milton Keynes: Open University.

YELLOWSTONE GEOTHERMAL AREA, WYOMING/MONTANA/IDAHO, U.S.A.

Porkchop Geyser, Yellowstone, in 1989. Since this time, a large steam explosion has destroyed the geyser. Photo by Roger Suthren

Geology:

• high volcanic plateau in a region of active major crustal extension, probably related to hot spot migration.
• active volcanism for at least the last 2.2 Ma
• predominantly rhyolitic, with subordinate basalts
• 3 major silicic eruptions associated with caldera collapse and voluminous ash-flow sheets at
• 2.0 Ma (collapse of 30 km diameter caldera, 2500 km³ ash flows)
• 1.3 Ma (250 km³ ash flows)
• 0.6 Ma (900 km³ ash flows)
• Composite caldera 70 x 45 km
• New influx of magma and resurgent doming from about 150,000 B.P
• large, shallow silicic magma body:
• ?45,000 km³
• total heat content of 1.125 x 10²³J, or 2.687 x 10²² cal
• responsible for much of present hydrothermal activity
• latest eruption ca. 70,000 BP (rhyolite lava)

A variety of geophysical anomalies coincide with the 0.6 Ma caldera:

• T greater than 350°C at very shallow depths
• low density
• large convective and conductive heat flow
• magnetic low
• low seismic velocities
• high seismic attenuation
• lack of earthquake foci deeper than 3-4 km beneath caldera
• sharp increase in electrical conductivity at ca. 5 km depth
• historical record of inflation and deflation

The hydrothermal system:

• recharge from meteoric waters from precipitation mainly on mountains to N and NW
• waters convect to depths of 4-5 km within caldera, reaching max. T of 350-430°C
• convective heat discharged by the system is ca. 1.7 x 10¹⁷J yr^-1
• 20% increase in heat discharge in 1983, year before the Mt. Borah earthquake
• activity has occurred at this level for at least the last 15,000 years
• is system cooling down or heating up?
• thermal energy from cooling of already crystalline rocks, from crystallizing magma, or both
• recent uplift suggests injection of new magma and/or liberation of fluid from crystallizing magma
• most hydrothermal activity occurs within the 0.6Ma caldera, close to ring fracture or at margins of resurgent domes, also along N-S fault system (e.g. Norris, Mammoth)
• reservoirs mainly permeable rhyolite flows at various depths, sandwiched between impermeable ash-flow tuffs
• in W part of Park, hot water systems dominate
• eastern systems are vapour-dominated (fumaroles, mudpots etc.)
• reservoir T ranges from 180 to 270°C
• springs emerge where faults cut basins
• most springs are neutral to slightly alkaline, and deposit siliceous sinter
• no exploitation of geothermal resources is likely in America's largest National Park

View of part of the Valles Caldera, New Mexico, showing the large resurgent dome where much hydrothermal activity is located. Photo by Roger Suthren

Geology:

• occurs at the boundary between the Colorado Plateau and the extensional Rio Grande Rift
• in the Rift, high heat flow is concentrated towards the W margin: highest heat flow values 250-670 mWm^-2
• closely related to Quaternary volcanic centres
• thus, local large igneous source is superimposed on large regional zone of high heat flow
• volcanism in Jemez Mts more or less continuous for the last 13 Ma, with a peak ca. 1.1 Ma ago (major ash flow eruptions)
• bimodal basaltic/silicic volcanism, with magma chamber >>3km depth
• Valles is a resurgent caldera

• recharge from streams fed from perched water tables in near-surface volcanic and sedimentary rocks
• some recharge from deep-seated geothermal waters
• springs occur either at intersections of perched water table with topography, or where there is upward movement of water along faults

• within the caldera is a high T hydrothermal system
• main resource is a liquid-dominated, underpressured system
• T up to 330°C
• surface expression is hot springs, fumaroles and rock alteration.
• production mainly from fractures in pumice-rich basal 300m of Bandelier Tuff
• wells 1500m to 2700m deep
• graben faults very important in controlling movement of hydrothermal fluids
• as they move down the hydraulic gradient, hot fluids cool and mix with colder ground waters, resulting in low enthalpy systems
• low T hydrothermal systems within the Jemez Mountains are exploited for balneology (look it up!) and small-scale space heating

• W of Valles is hot, dry rock of low permeability
• at Fenton Hill, two 3 km deep holes have been drilled, reaching T of ca. 200°C
• holes connected by hydraulic fracturing to produce heat exchange surface
• low water loss so far
• in 2nd test, depth of 4 km and T of 250°C reached
• heat reservoir is impermeable Precambrian basement.

• GOFF, F. & GRIGSBY, C.O. 1982. Valles caldera geothermal systems, New Mexico, USA. Journal of Hydrology, 56, 119-136.
• GOFF, F., SHEVENELL, L., GARDNER, J.N., VUATAZ, F.D. & GRIGSBY, C.O. 1988. The hydrothermal outflow plume of Valles Caldera, New Mexico, and a comparison with other outflow plumes. Journal of Geophysical Research, 93 (B6), 6041-6058.
• HEIKEN, G., GOFF, F., GARDNER, J.N. And BALDRIDGE, W.S. The Valles/Toledo Caldera Complex, Jemez Volcanic Field, New Mexico. Annual Review of Earth and Planetary Sciences, 18, 27-53.
  
  
• Resurgent Calderas and the Valles Caldera
• Jemez volcanic field & Valles Caldera, New Mexico
• Geothermal potential of Valles Caldera (pdf)
  

This page is maintained by Roger Suthren. Last updated 2 December, 2021 4:06 PM