Here is an excerpt from a great reference on Geysers:
A geyser is a hot spring that periodically erupts, throwing water into the air. Though that sounds simple, geysers are extremely rare. As of December 2005, the total of active geysers on earth number approximately 1000.
Conditions must be just right for geysers to occur. Three components must be present for geysers to exist: an abundant supply of water, an intense source of heat, and unique plumbing. Water is common in nature, heat can come from volcanic activity, but the plumbing is critical. For water to be thrown into the air, geyser plumbing must be water- and pressure-tight. Geyser scientists and observers have identified the volcanic rock rhyolite as being particularly effective at hosting geysers. Rhyolite is high in silica, which can deposit a water-tight seal along the walls of the geyser plumbing. Most of the geyser fields in the world are found in rhyolite or similar silica-laden rocks (like ignimbrite). The mixture of water, volcanic heat, and plumbing is exceptional at Yellowstone National Park. Over one-half of the world's geysers are located within the park's boundaries.
It is increasingly apparent that geysers must possess a fourth characteristic to exist: remoteness. Within the last fifty years, volcanic heat and abundant water have been increasingly harnessed to turn turbines for electricity production. Geothermal energy can be produced at any site where volcanic heat and water are readily available. Unfortunately, geyser fields are ideal for this type of energy production. Geothermal energy production steals the geysers' water, and destroys geyser activity (for example, Wairakei, New Zealand). A growing threat to geysers stems from mineral extraction. Hot groundwater may precipitate gold or other valuable minerals, and extraction may require removing the geyser plumbing itself. For example, in May 2003, mineral exploration at South America’s second largest geyser field (Puchuldiza, Chile), caused cessation in the field’s geysers. Few realize the actual rarity of geysers. As a result, many geyser fields have been destroyed and many others are being threatened.
Locations
Yellowstone National Park (USA)
Valley of Geysers, Kamchatka Peninsula (Siberia)
El Tatio (Chile)
North Island, New Zealand
Iceland
Beowawe Geyser Field, Nevada (USA)
Steamboat Springs, Nevada (USA)
Umnak Island, Alaska (USA)
Other World Geysers
At least a dozen additional locations worldwide are known to contain between one and fourteen geysers.
United States' Lesser Fields
Photographs of the United States' lesser geyser fields can be found at: (http://www.alanglennon.com/geysers/lesser).
Cold-Water Geysers
Approximately a dozen cold-water geysers exist in the world. Most of these are erupting man-made boreholes.