Blue Fire
The Kawah Ijen Volcano the island of Java has an active solfatara that emits hot, flammable sulfurous gases that ignite as they enter Earth's oxygen-rich atmosphere and burn with an electric blue flame. Some of the gas condenses in the atmosphere producing flows of molten sulfur that also burn with an electric blue flame.
The volcano has a one-kilometer-wide caldera lake filled with highly acidic water with a pH measuring as low as 0.5. It is the world's largest highly acidic lake. This extreme acidity and a high concentration of dissolved metals colours the lake a beautiful turquoise blue.
https://geology.com/volcanoes/kawah-ijen/