A volcano is an opening, or rupture, in a planet's surface or crust, which allows hot magma, volcanic ash 

and gases to escape from below the surface.Volcanoes are generally found where tectonic plates are diverging or converging. 

During a volcanic eruption, lava, tephra (ash, lapilli, volcanic bombs and blocks), and various gases are expelled from a volcanic vent or fissure. Several types of volcanic eruptions have been distinguished by volcanologists.