A geyser is a type of hot spring that periodically erupts with water and steam. These natural features are formed in areas with significant geothermal activity, where subterranean water is heated by proximity to magma or hot rock. The cycle of eruption is driven by the physical process of superheating water beneath a restricted crust or layer of rock. As the water reaches a critical temperature and pressure, the rapid phase change from liquid to steam drastically increases internal pressure. When this accumulated pressure exceeds the confining strength of the overlying material, the superheated water and steam are violently ejected through an opening, defining the characteristic eruption.