These images of blue lava are amazingly real! So what’s the mechanism behind?
What is actually happening at the Kawah Ijen volcano? What going on there? Why is this Indonesian volcano spewing blue lava? In few words: it’s not the lava itself that is responsible for the color, it’s the burning sulfuric gas that’s also being emitted during the eruption.
As explained by the Smithsonian Magazine:
This blue glow, unusual for a volcano, isn’t the lava itself. It is due to the combustion of sulfuric gases in contact with air at temperatures above 360°C. In other words, the lava—molten rock that emerges from the Earth at ultra-high temperatures—isn’t colored significantly differently than the lava at other volcanoes, which all differ slightly based on their mineral composition but appear a bright red or orange color in their molten state.
But at Kawah Ijen, extremely high quantities of sulfuric gases emerge at high pressures and temperatures (sometimes in excess of 600°C) along with the lava. Exposed to the oxygen present in air and sparked by lava, the sulfur burns readily, and its flames are bright blue. There’s so much sulfur that at times it flows down the rock face as it burns, making it seem as though blue lava is spilling down the mountainside. But because only the flames are blue, rather than the lava itself, the effect is only visible at night—during daytime, the volcano looks like roughly any other.
This video contains sequences of the blue lava @ 1:06 (the rest of the movie is in french):
Besides the seemingly blue lava, the high sulfuric content is also responsible for the potentially hazardous gas in the air, in which local miners in the area work to extract sulfuric rock from the volcano’s surface. (SOURCE)