A volcano is a mountain with an opening in the earth's surface, through which molten rock, ash and gases can escape. Volcanoes are usually found along the edges of tectonic plates, where the Earth's crust is being pulled apart or pushed together. There are three types of volcanoes: stratovolcanoes, shield volcanoes and cinder cones. Stratovolcanoes are tall and cone-shaped with steep sided and a crater at the top. Shield volcanoes are broad and flat, with gently sloping sided and a broad base. Cinder cones are small and cone-shaped, with steep sided and a hole at the top.