A volcano is an opening in the Earth's crust through which molten rock, ash, gases, and steam erupt. When molten rock, called magma, is beneath the surface, it rises and is expelled during an eruption, at which point it is called lava. Volcanic eruptions can create mountains as lava and ash accumulate around the vent with each eruption. Volcano Activity : Active, Dormant, Extinct. Eruption: The process of a volcano releasing material from the Earth's interior. Magma vs. Lava: Magma is molten roc