There are a few volcanoes around the world where the lava appears blue or has blue flames, but none that consistently exhibit blue flames as Kawah Ijen does. The electric-blue flames are caused by the combustion of sulphuric gasses in the oxygen-rich air. Through the combustion, the sulphuric gasses condense into blue molten sulphur that spills down the mountainside, in dazzling electric-blue flames through a phenomenon called electronic excitation. At such high pressure, sometimes the temperature reaches 600°C.
