How  Geysers Form


The question, how does a geyser form, can not be answered quickly. Geysers are temporary features geologically. The duration or " life span" of a geyser is at the most  several thousand years. Geysers are usually associated with volcanic areas. Their formation requires the combination of 3 specific geologic conditions that are usually found in volcanic terrain: 1- intense heat, 2- Water, 3-a plumbing system. The fact that they need heat much higher than normally found near the earth's surface is the reason they are usually associated with volcanoes or volcanic areas. Click below to find out more about the conditions necessary for geyser formation.




Water- A Needed Component in Geyser Development

Superheated water is the needed in order for geysers to form. The heat comes from a buried magma chamber in an volcanic setting. Water is more easily obtained than the heat. The water comes from the groundwater system in the geyser basin. It starts as precipitation and enters the ground water system by percolating down through porous sand and gravel as well as cracks and fissures in the earth. The surface water recharges the water that circulates in the subsurface and is eventually erupted from a geyser or flows out of hot springs. The water does not need to necessarily be present in great volumes on the surface. Geyser do occur in desert environments. In fact some the geysers in Chile occur in one of the the driest valleys in the world. What is important is that water is available, and that it can circulate deep into the earth's surface where it can approach the heat source. It is estimated that it takes several hundred years for the water in Yellowstone to fall as rain or snow, enter the groundwater system, circulate deep down near the heat source and then rise to near the surface where some of it is erupted from geysers. Surface conditions such as droughts or extremely wet periods may not effect geyser eruptions or hot spring flow for hundreds of years. Cooler water in the near surface also mixes with the rising superheated water and may play a role in a geyser's eruption and timing.





Heat Source




The heat needed for geyser formation comes from liquid rock or magma when it is near the surface of the earth. That is why  geysers and volcanoes are found in the same area. When the magma reaches the surface, a volcano is formed. Geysers, though rare, are found in the same geologic settings where volcanic heat sources are available. These settings are listed below:
Convergent Margins
  Convergent plate margins occur where one of the earth's plates is being subducted under another. The friction causes the rocks in and around the  subducting plate to melt and the molten rock moves toward the surface. The rising magma then forms volcanoes. Geysers in Chile, New Zealand, Russia, Mexico and Japan are found in this geologic setting. To find out more about convergent plates and subduction zones check out these web sites:

For a good discussion of plate tectonics see: Introduction to Plate Tectonics -  on the volcano world site.

Divergent Margins
  In Divergent Margins, where rifting is occurring, the plates are moving away from each other. In the oceans, the splitting of the crust or rifting allows magma to reach the surface. Molten rock spills to the surface along these fractures and new oceanic crust is formed. Sometimes continental crust is located at the plate boundaries where the plates are or are starting to move away from each other. On the continental crust when rifting occurs large cracks known as rift valleys form. As the heat from the mantle rises along these big cracks, magma forms and rises to the surface which, in turns, results in volcanic activity. Geysers are found along divergent margins or incipient rift basins where continental crust is involved. Examples of geysers in this setting are found in  Iceland, Nevada, and Kenya. For more information on divergent margins and rifting see the web pages listed above but make sure you check out this great site:

Hot Spots/ mantle plumes

  While most volcanic activity and related geyser development occur along the plate boundaries described above, sometimes volcanic activity can be found far from these boundaries. Yellowstone and the Hawaiian Islands are examples of these types of areas. It is theorized that these areas are due to hot spots or localized thermal convection in the mantle of the earth called plumes. The hot spot is stationary and the plates move over them. Much controversy still is found among geologist about hot spots. Much remains to be learned about the mechanism that causes plumes to form. For a thorough description see:

The geysers in Yellowstone lie in a large volcanic feature called a caldera. For info on calderas see:




Geyser Plumbing Systems

In order for the heated water to form a geyser a plumbing system is needed. This includes a reservoir to hold the water while it is heated. The geyser plumbing system is not well understood but we do know that it is probably formed by a combination of spots of porous rock, in the case of Yellowstone, gravel deposited by a glacier, and cracks and fissures in the earth. Geysers often are aligned along faults, the cracks in the earth formed by earthquakes. The plumbing system is made up of a system of fractures, fissures, porous spaces and sometimes cavities. Constrictions in this system are important to the building up of pressure before an eruption. For pictures of plumbing systems and more info try this site:





Silica Seal

If the 3 factors, heat, water and a plumbing system, are present then flowing hot springs  are possible. Hot springs and fumaroles are very common in volcanic areas, in fact, they are found in almost every volcanic area on earth. Geysers, however, are found in a small fraction of the volcanic areas. The factor missing in most areas is strong rock formations surrounding the thermal areas. Silica linings or seals on the plumbing system seem to be important to maintain the integrity of a plumbing system that is subject to  the intense pressures caused by geyser activity.  In Yellowstone's  geysers basins, silica cements much of the glacial gravel near the surface and is deposited in white sheets across the surface. The silica forms a rock called sinter or geyserite. The source of silica is believed to be rhyolite, a light colored, silica rich volcanic rock. Hot ground waters dissolved silica from the rhyolite and related rocks and carry it in solution. As the silica rich water moves near and on the surface the silica comes out of solution and is deposited as sinter. The sinter coatings on the plumbing system is able to hold back the pressure and provide a seal that allows the geysers to build enough pressure to erupt. Without the silica seal, a thermal feature will just be a hot spring and not a geyser.   Most experts agree that the presence of the volcanic rock rhyolite is the key to the amount and quality of silica needed for geyser development. Large deposits of rhyolite are rare on or near the earth's surface. One of the notable exceptions are the rhyolites of the Yellowstone Plateau.

This photo show silica (sinter)  formations that were once found around Sapphire pool in the Upper Geyser Basin. The silica "biscuits" were destroyed by large eruptions. Photo by Haynes from the Gregory Jones Collection. 

Related Questions

Where does heat to form geysers in Yellowstone come from?





























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1999, 2006 Gregory L. Jones. All rights reserved.
Revised: March 12, 2006.