The Ijen vulcan’s crater (located in east Java Island, Indonesia) has a Blue Flame phenomenon, there are only 2 in the world (the other one is in Iceland) and can be seen only at night.
The liquid sulfur has caught fire and burns with an eerie blue flame. Acidic gases rise with smoke among yellowish chunks of sulfur. Inside the Kawah Ijen crater lies a one-kilometer-wide acidic lake.
There are plenty of natural treasures hidden away in the most unsuspecting places on Earth. One of them is an Indonesian sulfur mine, Kawah Ijen, that produces stunning, spectral blue lava.
Kawah Ijen is a part of the Ijen volcano complex – a group of stratovolcanoes in East Java, Indonesia – with an active crater that’s 200 meters deep. The complex is also home to the world’s largest turquoise-colored acidic lake, full of sulfuric acid. The lake is a sulfur mining site; miners carry sulfur-laden baskets by hand from the crater floor.
The miners work at night to double their meagre income, but they don’t have to worry about the dark. Kawah Ijen, an ordinary rocky crater by day, transforms into a stunning display of electric blue light at night.
Source: Indonesian Volcano Spews Hauntingly Beautiful Blue Lava