If heat, geyserite and water are present, but not the right shape, you can get a simple hot spring. Without the constriction at the top of the spring's plumbing system, the boiling water simply flows up to the surface and gently into a pool. Very hot springs are extremely clear as the water is pure and too hot to support the growth of algae or most bacteria as a normal stagnant pond would. While the water is pure, it is not recommended for drinking as small amounts of dissolved minerals, such as arsenic and sulfur, may be present. Most pools have a deep blue color caused by the absorption of all other colors of the light spectrum by the water.
Pools can sometimes turn into geysers and visa versa when conditions change.
Sometimes a hot spring only known to be a pool will surprise watchers when it erupts and turns into a geyser without warning, though such events are rare. Probably the most famous geyser in the world is Old Faithful at Yellowstone National Park. It was named by members of the Washburn Expedition of 1870 because it is the most frequently erupting and predictable of the big geysers. Old Faithful sends up 8,400 gallons as high as 184 feet on an average of every 85 minutes. By measuring geyserite deposits on the cone and carbon-dating pieces of wood caught in the geyserite, scientists have estimated that Old Faithful is roughly 300 years old.