Glaciovolcanism is volcanism and related phenomena associated with glacial ice. The ice commonly constrains the erupted material and melts to create meltwater. Considerable melting of glacial ice can create massive lahars and glacial outburst floods known as jökulhlaups.
Three forms of glaciovolcanism are known. Subglacial eruptions occur when a volcano erupts under ice. Such activity can produce landforms such as tuyas and subglacial mounds. Ice-marginal volcanism takes place when material from a subaerial eruption makes lateral contact with ice. Ice-marginal lava flows are a product of this phenomenon. Supraglacial eruptions deposit ejecta onto the surface of an ice sheet.