Ijen crater

 Ijen crater
Ijen crater is one of several volcanoes located in the 15km diameter Ijen Caldera in E Java, Indonesia. The caldera rim is still visible in places, but has been partially buried by Kawah Ijen, 2800m high Gunung Merapi (not to be confused with Merapi volcano near Yogyakarta), Gunung Rante and Gunung Pendil volcanoes. The caldera is today largely filled with coffee plantations. Kawah Ijen harbours a large warm acidic crater lake and an active sulphur mine. Due to its easy accessibility, turqoise lake and unique sulphur mining operation, the crater is regularly visited by tourists. The last recorded magmatic eruption of Kawah Ijen was in 1817. The eruption displaced the crater lake and resulted in inundation of several villages along the drainage route. Phreatic eruptions have been reported in 1796, 1917, 1936, 1950, 1952, 1993, 1994, 1999, 2000 (also minor ash emission), 2001, 2002 (with minor ash emission), (?), 2011. The increasing frequency may reflect better reporting since the explosions are usually confined to the lake and cause little or no damage.

Various unverified sources claim that sudden gas release from the crater lake claimed the lives of numerous sulphur workers in 1976 (11-49) and 1989 (25). Such gas releases may occur with little warning in the future and probably represent the main hazard for visitors.


Kawah Ijen Volcano
Kawah Ijen Sulphur Mine
Crater of Kawah Ijen volcano containing highly acidic lake and solfatara (bottom left)
Sulphur Mining at Kawah Ijen solfatara


Kawah Ijen volcano, Solfatara, Sulfur Mine, Sulphur, Acidic crater lake Kawah Ijen volcano, solfatara. Yellow sulfur deposits
Solfatara on flank of crater above acid lake Natural sulfur pot damaged by miners


Many properties of sulfur (= sulphur) can be observed at the Kawah Ijen sulfur mine. The element tends to form polyatomic molecules such as the predominant cyclic form octasulfur. The cyclic structure changes its exact form at different temperatures. Melting temperature is about 115 'C with a boiling point of 444 'C. Significant vaporization, often incorrectly referred to as sublimation, occurs below the boiling temperature. Molten sulfur tends to get darker in colour as temperature increases, with orange flows often visible over the background of yellow solidified sulfur deposits. Sulfur can also self-ignite at temperatures as low as 248 'C and burns with a blue flame as sulfur dioxide gas is formed. These flames are a well-documented feature of Kawah Ijen and can be clearly seen at night. Several small fields of sulfur flares can be seen at the top of the active part of the solfatara. Burning flows of molten sulfur have been documented in the past, but workers presently rush to extinguish such flows as the resulting dark material is of no commercial interest for the miners.



Kawah Ijen volcano, Blue sulfur flames, Sulphur flare Kawah Ijen volcano, burning sulfur flow, river of burning sulphur
Close-up of sulfur flare Small burning sulfur flow during daylight


Kawah Ijen volcano, burning sulfur flow Kawah Ijen volcano, Solfatara, Sulfur Mine, Sulphur, Acidic crater lake
Burning sulfur oxidizes to reddish dioxide Nighttime view of crater with blue flames at base of gas column


Kawah Ijen volcano, solfatara with blue sulfur flames and acidic crater lake. Nighttime view. Kawah Ijen volcano, solfatara with blue sulfur flames and acidic crater lake. Moonlight.
Areas of burning sulfur in mine Areas of burning sulfur in mine


Pipe, Kawah Ijen Sulphur Mine Sulphur Flow, Kawah Ijen Sulphur Mine
Pipe used to extract molten sulphur from the solfatara Small molten sulphur flow


Kawah Ijen volcano solfatara, molten sulfur bubbling Kawah Ijen volcano solfatara, sulfur sulphur stalagtites
Sulfur frothing as if boiling, probably due to moisture under flow Molten sulfur forms stalagtites


Kawah Ijen volcano solfatara, molten sulfur flow Kawah Ijen volcano solfatara, molten sulfur flow
Molten sulfur flows over smashed up older deposits Molten sulfur flows over smashed up older deposits


The volcanic gases emitted are also responsible for the characteristics of the nearly 200 meter deep crater lake. Takano et al., 2004 (J. Volc. and Geotherm. Res. 135, p.299-329) extensively studied the crater lake. Injection rates of 340 tonnes/day of sulphur dioxide were calculated, accounting for the extreme acidity. Lake temperature and pH fluctuate and were reported at around 36'C and 0.1, respectively, near the surface in this study.



Kawah Ijen volcano, Solfatara, Sulfur Mine, Sulphur, Acidic crater lake Kawah Ijen volcano, Solfatara, Sulfur Mine, Sulphur, Acidic crater lake

Kawah Ijen Acidic Crater Lake


Fisheye view of Kawah Ijen crater lake Kawah Ijen Volcano, Java, Indonesia
 Ijen Crater  Ijen Crater


Kawah Ijen volcano, Acidic crater lake, sulfur rafts on surface Yellow scum floating on Kawa Ijen acidic crater lake
Rafts of yellowish material floating on lake Close-up of yellow "scum" floating on lake


Temperature and acidity change, along with visible lake surface changes such as colour fluctuations or local bubbling or upwelling can provide signs of increased activity along with seismic data which are regularly obtained. Also, observations by the mine workers can be taken into account, such as increased breathing difficulty or dizziness, suggesting changes in gas composition or levels. Interestingly, reports of birds falling into the lake (presumably due to intoxication by volcanic gases) have also been taken into account when assessing the risk of impending eruptions (Smithsonian Global Volcanism Program report 06/1997 (BGVN 22:06).



Images of Sulphur Mining Operation



The sulphur mining operation consists of a number of pipes driven into the solfatara. Solfatara temperatures nearing 250 'C have been reported, although chemical analysis of solfatara gases suggests temperatures inside to be above 300'C. Condensation of volcanic gases saturated with elemental sulphur (formed by SO2 + 2H2S = 3S + 2H2O reaction) occurs as they cool during passage through the pipes. Molten sulphur trickles out of the end of the pipes, solidifying nearby as it cools further. The miners then break up the sulphur deposits and carry them out of the crater and, via the weighing station, to a nearby sugar refinery. From there they are transported to a processing facility in a nearby town. Due to unprotected exposure to volcanic gases and loads of up to 100kg per trip, the life expectancy of the miners is low (not much over 30 years).


Kawah Ijen volcano solfatara, sulfur mine. Kawah Ijen volcano solfatara, sulfur mine.
Solfatara with sulfur mine Solfatara with sulfur mine


Kawah Ijen volcano solfatara, sulfur mine. Kawah Ijen volcano solfatara, sulfur mine.
Solfatara with sulfur mine Solfatara with sulfur mine viewed from crater rim



Kawah Ijen volcano, sulfur mine. Miner with hose. Kawah Ijen volcano, sulfur mine. Worker hosing down pipes with water for cooling.

Worker waits for water to cool piping Worker spraying water onto solfatara



Miners, Kawah Ijen Sulphur Mine Pipe, Kawah Ijen Sulphur Mine
Miners working in intense gases with merely handkerkiefs for protection. Fresh sulfur deposit below pipe


Molten sulfur dripping from pipe at Kawah Ijen sulphur mine Molten sulfur dripping from pipe at Kawah Ijen sulphur mine
Condensating sulfur dribbling from pipe Condensating sulfur dribbling from pipe


Kawah Ijen volcano, Solfatara, Sulfur Mine, Sulphur, Worker breaking up deposits Kawah Ijen volcano, Solfatara, Sulfur Mine, Sulphur, Worker breaking up deposits

Worker breaking up sulfur accumulations at end of pipes



Kawah Ijen volcano, Solfatara, Sulfur Mine, Sulphur, Worker carrying sulfur in baskets Kawah Ijen volcano, Solfatara, Sulfur Mine, Sulphur, Worker lifting baskets with sulfur

Classic means of transporting sulfur at Ijen Lifting heavy baskets full of sulfur


Sulphur Miner Kawah Ijen Volcano Mine Kawah Ijen volcano, Solfatara, Sulfur Mine, Sulphur, Worker at sulfur weighing station
Miner resting along climb from crater Worker attaching sulfur load to weighing station


Kawah Ijen volcano, Solfatara, Sulfur Mine, Sulphur, Worker at sulfur weighing station Kawah Ijen volcano, Solfatara, Sulfur Mine, Sulphur, Worker weighing sulfur
Weighing sulfur Adjusting weights on scales


Important Visitor Information



Levels of gas at Kawah Ijen can reach dangerous levels, especially in the immediate vicinity of the solfatara. Depending on the wind direction, the trail into the crater may be shrouded in gas. Visitors should only visit the solfatara / mine with a gas mask having a suitable filter for removing a large proportion of the largely acidic gases. In the immediate vicinity of the sulfatara, even standard gas masks may not be able to cope with the high gas concentrations downwind (personal experience), potentially causing irreversible damage to the lungs. The acidic nature of the gases also leads to irritation and inflammation of the eyes.


Further, sudden releases of large volumes of gas from the lake may be fatal to those near the bottom of the crater.

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