The sulphur is produced around the volcano and then when it combines with the air it bursts into flames. Sometimes the gas condenses, sinks closer to the ground and so when it ignites it appears to look like blue lava flowing down the slopes of the volcanoes where it is found.
Blue lava locations
Blue lava, blue sulphur flames or rivers of blue flames can also sometimes be found in Yellowstone National Park, USA. In the Danakil Depression in Ethiopia the blue rivers of flames can be found on the ground near hydrothermal vents and also at its Dallol volcano.
Why only 'blue lava' at these locations?
There are lots of volcanoes so why is so much sulphur produced or ignited at these few locations?
There is so much sulphur at the Kawah Ijen crater they actually mine it.
Why does the Kawah Ijen volcano produce so much sulphur? Why does it come out of the ground in Ethopia?