Hot magma, melted rock below Earth's crust, rises and collects in a magma chamber (1) deep below the surface. If the magma flows through a conduit (2) up to a vent (3) on the surface, then it may cause an eruption and form a volcano.

Gases, lava (4), and pyroclastic material (5) are erupted from volcanic vents. The mountain that forms from layers of lava and tephra is called a volcano (6). The word "volcano" comes from the name of a Roman god, Vulcan, who was the god of fire. Magma that solidifies inside a volcano can form dikes and sills (7).

Volcanoes are classified as active, dormant or extinct.