Definition
A geyser is a hot spring that intermittently erupts jets of steam and hot water. This phenomenon occurs when groundwater is heated by magma deep underground. Pressure builds up until it overcomes the surrounding constraints, resulting in a spectacular eruption. Think of it like a natural pressure cooker that occasionally blows its top. Geysers are relatively rare and found in areas with volcanic activity. The most famous geyser is Old Faithful in Yellowstone National Park.