● Kawah Ijen is a volcano of blue lava.

The Kawah Ijen volcano complex is a group of stratovolcanoes in the Banyuwangi Regency of East Java, Indonesia. 

It is inside a larger caldera Kawah Ijen, which is about 20 kilometers wide. The Gunung Merapi stratovolcano is the highest point of that complex.

The name of this volcano resembles that of a different volcano, Mount Merapi in central Java, also known as Gunung Merapi; there is also a third volcano named Marapi in Sumatra. The name "Merapi" means "mountain of fire" in the Indonesian language.

West of Gunung Merapi is the Kawah Ijen volcano, which has a one-kilometer- wide turquoise -colored acid crater lake.

The lake is the site of a labor-intensive sulfur mining operation, in which sulfur-laden baskets are carried by hand from the crater floor. The work is low-paid and very onerous.

Its characteristic blue color is due to large amount of sulfur containing.
Images from:  Olivier Grunewald.

Video related to the topic: