A geyser is a hot spring that is in a lot of pressure that erupts as a jet of steam that goes in the air.
Geysers are made from a tube-like hole in the Earth's surface that goes deep into the crust (underneath the Earth's surface). The tube is filled with water. Near the bottom of the tube is molton rock called magma which heats the water in the tube to make the very hot steam.
They are all different sizes all over the world, but some geysers let out about thousands of litres of boiling water into the air. You definitely don’t want to be too close when that happens. This can go higher than a hundred metres into the air so you can hurt yourself.
Geysers are springs that send powerful jets of steam and water into the air from time to time. They are found in places where rocks are quiet close to the surface that have been heated. Many geysers therefore are found in the same areas as volcanoes or where volcanoes have been active. Geysers are not the only signs that there are hot rocks near the surface. Bubbling pools, hot springs and mud pools are in fact much more common than geysers. Sometimes when there is little water available puffs of steam or gases with breathtaking smells are the only signs.
Geysers are usually found with spouters, hot springs, mud pots and fumeroles, making a region called a geyser field. Each feature of the geyser field is produced as a result of water travelling between hot underground rocks. The type of feature is found in any geyser field simply depends on the local underground 'plumbing'. Geyser fields are usually easy to spot because the ground surrounding them is often clear of all plants and surface of the ground is a greyish-white colour.
Geysers regularly spurt water high into the air. You know where a geyser will erupt because there is a hole in the ground or a raised nozzle through which it will spurt. However, because the geyser's 'plumbing' is hidden deep below the surface, it is very difficult to tell when a geyser will erupt. This makes geyser-watching even more exiting.
Water from a geyser is guided out of the ground by a nozzle in much the same way as water comes out of a fire hose; the smaller the nozzle, the greater the pressure builds up in the passageways and higher the geyser erupts. The nozzle is formed from the dissolved minerals as they are deposited at the surface. Sometimes it only resembles a low mound, at other times it looks more like turret of a castle. As a result many geysers are named after the shapes of their nozzles. The nozzle rises from a boarder mound of grey rock called a platform.
Geysers of the world
The world's biggest active geyser is found in Yellowstone (USA),
Old Faithful is the world's best known geyser located in the park. Old Faithful erupts every 60 to 90 minutes and blasts a few thousand gallons of boiling hot water between 100 and 200 feet into the air.
The land of a thousand smokes is the name given to the area of Yellowstone National Park in Wyoming, USA. This is the largest US National Park covering 8,982 square kilometers, but the geysers hot springs and terraces are in several small areas. There are about 200 geysers and 10,000 hot springs.
Closer to home, in the North Island of New Zealand there is a region that still has active volcanoes. In the Whakarwarewara Thermal Reserve, Roturua, the largest geyser ever known to erupt, used to erupt to 450m every 6 to 15 hours, but it blew itself out in 1917.