A volcano was a mountain from which lava flowed out. It also produced large quantities of black smoke that could block out the sunlight. Volcanoes that erupted regularly were called active, while those temporarily devoid of external activity were referred to as dormant. The planet of Mustafar was covered in active volcanoes, while those of Kadavo were dormant for the most part. Sometimes, the lava of a volcano would cool rapidly, forming black volcanic glass or black sand.