A volcano is formed when magma (Lava) spews up from deep within the earth. After each eruption the Volcano gets bigger and bigger, so basically after periods of time the volcano will get larger. Lava will rise in cracks in the earth or weak spots in the earths crust. The pressure is relieved thus resulting in a volcanic eruptions it forms the new crust and then eventually builds up in that spot making a volcano. They also form in places called hot spots and various other places.
