A geyser is a natural hot spring that periodically erupts, sending a column of hot water and steam into the air. This phenomenon occurs when underground water is heated by magma or hot rocks, creating pressure that eventually forces the water to the surface. The eruption can last from a few seconds to several minutes, depending on the geyser. Famous geysers, such as Old Faithful in Yellowstone National Park, are popular tourist attractions. Geysers are part of a larger geothermal system, which includes hot springs and fumaroles, and they provide valuable insights into the Earth's geothermal activity.