Yellowstone National Park has the earth's biggest collection of geysers (Old Faithful being the most famous), bubbling mudpots, steaming fumaroles and brilliantly coloured hot springs.

Yellowstone's most famous items are the hydrothermal features found throughout the park. These features are the result of a 'hot spot', a section in the park, where the thickness of the earth's crust is very thin. The magma below the crust is less than 2 miles thick and the planet's internal heat is closer to the surface here, than anywhere else on earth.

Heavy precipitation in this area seeps down through the ground until it's superheated, then begins to rise, and eventually returns to earth as a geyser, hot spring, mudpot or other hydrothermal feature. This entire process takes approximately 500 years.

Geysers are identified by their eruptions, which are unpredictable. The majority of world's geysers are found here in Yellowstone, and can reach heights of 300-400 feet, with temperatures over several hundred degrees.