I’d seen this story a while back but did not buy the “blue lava” bit. That indeed was wrong – the blue is from gases.

Stunning Electric-Blue Flames Erupt From Volcanoes.

For several years Paris-based photographer Olivier Grunewald has been documenting the Kawah Ijen volcano in Indonesia, where dazzling, electric-blue fire can often be seen streaming down the mountain at night. “This blue glow—unusual for a volcano—isn’t, of course, lava, as unfortunately can be read on many websites,” Grunewald told National Geographic in an email about Kawah Ijen, a volcano on the island of Java. The glow is actually the light from the combustion of sulfuric gases, Grunewald explained.

There were no filters used to produce the blue glow in the pictures, which can only be photographed at night. This large amount of molten sulfur is very unusual. The lake at the crater is made of hydrochloric acid. This place will kill you for sure: notice in the video below, they must wear respirators in order to breathe. The yellow mineral on the ground is solid sulfur which is mined at this site. It’s extremely beautiful to watch.