The opening at the top of a volcano is called a vent and is where lava flows from erupting volcanoes. Volcanic vents usually sit inside craters, which are circular depressions in the ground.
Volcanoes are ruptures on the crusts of planets, such as the Earth. These ruptures allow hot gases and lava, as well as volcanic ash, to leave the magma chamber under the planetary surface. Volcanic vents come in a variety of shapes and sizes, depending on the gas content of the magma that leaves the volcano. Examples of these shapes and sizes include spatter vents, cinder cones and satellitic shields.