What forms when a spring is geothermally heated to the point that the water bursts throughout the surface in an upward stream of water and water vapor?

A geyser is formed when a spring is geothermally heated to the point that water underground reaches its boiling point and erupts through the surface in an upward stream of water and water vapor. The pressure from the boiling water builds up underground until it is released in a geyser eruption.