Ijen Caldera

The Ijen caldera complex is a 20 km wide, circular caldera depression that formed over 50,000 years ago as a result of the collapse of the old Ijen stratovolcano due a major eruption. The caldera contains more than 15 postcaldera volcanic cones. Kawah Ijen is the the only currently active system.

No recent oberved lava emission, mainly phreatic activitity (steam).

Activity :1976, 1817, 1917, 1936, 1952, 1993, 1994, 1999, 2000, 2002, 2012. The most recent significant eruption of Kawah Ijen occurred in Jan–Feb 1817. 

Since the beginning of the twentieth century, a concrete dam on the west side of Kawah Ijen’s crater has controlled the lake overflow.


The Lake

The lake, located at 2200m has a regular oval shape (600 x 1000 m), it could fill 11 000 olympic swimming pools. It is recognised as the largest hyperacidic crater lake in the world. The lake generally has a green color due to chloridric and sulfuric acid with floating yellow deposits of sulphur at the surface.  

It is also the source for the Banyupahit river, resulting in highly acidic and metal enriched water which has a significant effect on the downstream river ecosystem.


Research indicates the release of molten sulphur and gases at the bottom of the lake. The lake surface temperature is influenced by rainfalls, sometimes creating a cold an isolating layer keeping the gases trapped inside. A dangerous situation as their release is unpredictable.


Blue Fire

The blue fire is ignited sulphuric gas, which emerges from cracks at temperatures up to 600 degrees Celsius (1,112 degrees Fahrenheit). Exposed to the oxygen present in air, the sulfur burns readily, and its flames are bright blue. Those gases are directly originated from the magmatic chamber under the volcano. The flames can be up to 5 metres high, It is the largest blue flame area in the world.


Sulfur Mine

Sulfur Melting T°: 112,8°c   Boiling T°:   444,6°c

Gases temperature from the fumarolles can vary from less than 200°c to greater than 600°c. Gases are then collected throught pipes to help the cooling process and condensate  to form solidified rocks made of almost pure  sulfur . From orange when hot, sulfur turns yellow when cooling down. 


The Hike