Volcanoes are a type of mountain. Volcanoes have rock beneath the earth. When pressure builds up inside the volcanoes, they erupt. Shooting fragments of lava into the air, or spilling lava, rock, poisonous gasses and ash with great power over the side of the mountain or into the air. Over time volcanoes can get bigger and bigger.
fun fact The largest active volcano is Mauna Loa, this volcano is located in Hawaii.