Volcanoes are mountains that sometimes erupt, shooting gas, ash, and burning rock. Inside volcanoes is a deep hole containing hot magma that can push to the surface, forming a crater and flowing as lava. Different types of volcanoes include active volcanoes that can still erupt, dormant volcanoes that are currently sleeping, and extinct volcanoes that cannot erupt again. Some examples of active volcanoes are Kilauea in Hawaii and Arenal in Costa Rica, while Mount Fuji is currently dormant. The eruption of Vesuvius in Italy buried the city of Pompeii under ash.