A geyser is best described as a fountain of superheated water and steam that erupts from the ground periodically. It is a natural phenomenon that occurs when groundwater is heated by geothermal activity deep below the Earth's surface. As the water heats up, it expands and rises towards the surface. When the pressure builds up enough, the water and steam erupt in a powerful geyser. The eruption can last from a few seconds to several minutes, and the height of the water and steam can range from a few meters to over 90 meters. Geysers are found in areas of geothermal activity, such as Yellowstone National Park in the United States, Iceland, and New Zealand.