The images below are of Indonesia’s Kawah Ijen Volcano.
The reason for its amazing blue hue is the sulfur content is incredibly high. When the sulfuric gas comes into contact with the air it combusts creating bursts of neon blue light. Some of the sulfur condenses and begins to flow down the side of the mountain. The rest erupts into flames.
So far to date this is the only known volcano in the world to do this.
You can check out more of Oliver’s amazing photogrpahy at his website Oliver Grunewald