Photographer Olivier Grunewald captured the stunning picture above of the Kawah Ijen volcano in Indonesia, first published in National Geographic.

The glowing, electric-blue flames are caused by combustion of sulfuric gases. The gases vent from cracks in the volcano with high pressure and temperatures reaching up to 600 degrees Celsius (1,112 degrees Fahrenheit). Once they come in contact with the air, the gases ignite, sending flames shooting as much as 16 feet high.

Cool to watch, from a distance ;)

Yes, from a great distance!

The gases can also condense into liquid sulfur "which continues to burn as it flows down the slopes," said Grunewald, "giving the feeling of lava flowing."  (bottom picture)