The main features of a volcano include a vent, a summit crater and a magma chamber. The vent is an opening through which volcanic material is erupted. Volcanoes can have more than one vent. The summit crater is the large concave opening that holds the central vent at the top of the volcano. The magma chamber is the large pool-like structure inside the volcano that holds the magma.
When a volcano erupts, the magma is spewed from its chamber through the main vent. Lava, rocks, ash and other debris shoot out or roll over the volcano's sides. The volcano's actual structure accretes over time. After each eruption, the lava and other volcanic material cools around the volcano and creates a hard layer of rock.
Volcanoes can have more than one opening around the main vent. These are called cones and fumaroles. These are fractures in the volcano that open up to also release volcanic material and volcanic rocks.
Volcanoes are further classified by their shapes, their composition and their eruption patterns. The three main types are stratovolcanoes, shield volcanoes and scoria cones. Stratovolcanoes have steep upward slopes with a small crater at the top. Shield volcanoes are slightly sloped hills. Scoria cones are the most common type of volcano. They are short, hilly formations with steep slopes and a large crater at the top.