A volcano is a geological feature formed by the eruption of magma onto the Earth’s surface, creating a mountain or hill with a vent through which lava, ash, and gases are expelled. Volcanoes are significant in geology for understanding the processes of magma generation, the dynamics of eruptions, and the formation of volcanic landforms.
Source Francis, P., & Oppenheimer, C. (2004). “Volcanoes.” Oxford University Press.