The mysterious blue lava 2

The images are real and not from Photoshop. In the video, a volcano in Indonesia overflow blue lava. So what is happening here?

Olivier Grunewald is nature photographer (, Régis Etienne passionated about film and President of the SVG (Volcanology Society of Geneva).
In 2008, they hear about blue flames in the heart of Kawah Ijen volcano in Indonesia, known for its acid lake and its sulfur mine.
Olivier and Regis will return for several years. They will spend 30 nights into the crater in the middle of extremely corrosive gas, trying to bring back images of these unique volcanic phenomenon.
At nightfall, a glow quite unusual for a volcano appears at the bottom of the crater. Ignited sulfuric high temperature gas produce an electric blue flares, sometimes reaching five meters high.
They will also discover that minors come also in the middle of the night to collect thanks to the torches light the coagulated blood of the volcano.