Kawah Ijen is an active volcanic crater lake about 45 km northwest of my site. It is a place of scientific wonder, industry, and great beauty. Vistas from Ijen have been shared by The Boston Globe, The New York Times, and the BBC while the lives of the local sulfur miners have been chronicled on an episode of the BBC’s Human Planet and in the documentary Workingman’s Death (highly recommended).[*1] I think there is still more that can be shared about this special place. Here I provide some information on the (1) Geology and Geography, (2) Eruptive History, (3) Scientific Study Outside of Physical Volcanology, and (4) Tourism and Attraction at Kawah Ijen. I’ve also listed some additional resources in the (5) Footnotes, if you want to explore things further.
1, Geography and Geology
Kawah Ijen is one part of the much larger Ijen Caldera Complex. The Ijen Caldera Complex is approximately 22 km wide and partially rimmed by a series of volcanic summits with violently eruptive geologic histories. These peaks dominate the horizon beyond the rice fields just north of my site (Figure B). In addition to the trace of violent eruptions, the Ijen Caldera Complex is also dissected by a roughly E-W lineament of small hills that were formed by effusive eruptions in past geologic time. Kawah Ijen lies at the intersection of these two trends.
The lake of Kawah Ijen is located on the flanks of Gunung Merapi[*2]—one of the prominent summits on the western edge of the caldera. The lake is approximately 500 m by 800 m across and reaches a maximum depth of 200 m (Figure D). Containing an estimated volume of 40×10^6 m3 at an average pH of 0.4, Kawah Ijen is popularly described as “the world’s largest collection of acidic waters.” These waters are held back by a dam to prevent flooding into the coffee plantations below, but the water still drains via the Banyupahit and Banyuputih rivers towards the Asembagus irrigation area. I will leave a discussion of those two aptly named rivers and the health consequences of downstream irrigation for later in this post.
In the context of the greater Indonesian volcanism, Ijen is roughly in line with other nearby volcanic massifs such as Iyang-Argapura, Tengger-Semeru, and Raung (Figure C)—a linear trend that extends from the northern tip of Sumatra all the way through Nusa Tenggara (aka Lesser Sunda Islands). Along this spine—and at Ijen—there is a general trend of older to younger volcanism in the direction from north to south.
2, Eruptive History
Historically, eruptions from Kawah Ijen have been small and phreatic[*3] in nature. The location of Merapi and Kawah Ijen on the ring of more volatile peaks leads some people to ponder and plan for a historically unprecedented violent eruption, but the eruptions from the geologic and historic record have been consistent only with the more effusive trend only. Though Ijen is only expected to produce minor eruptions, the effects could still be devastating due to the close proximity of both residents, workers, and tourists.
A video of an eruption from Volcán Poás—a volcanic crater lake in Costa Rica—provides a likely analog for plausible activity at Ijen. The local geography and population exposure around Poás stand in stark contrast to that of Kawah Ijen (Figure E and Video A).
THIS IS NOT A PHOTO OF IJEN!!!!!! (Poás, Costa Rica)
THIS IS NOT A PHOTO OF IJEN!!!!!! (Poás, Costa Rica)
CLICK ON THE LINK TO GO TO THE YOUTUBE VIDEO by JUANCHANTO
In this video, a relatively small eruption[*4] from Poás is safely viewed by tourists at the crater viewpoint nearly one kilometer from the lake. At Kawah Ijen, hundreds of people live within one kilometer of the crater, and hundreds more tourists and workers hike within one hundred meters of the lake (or directly to its shores) every day. One can imagine the devastation the eruption from this video would have wrought had it occurred unexpectedly at Ijen.
The population density around volcanoes presents a challenge to hazard monitors throughout much of Indonesia. Because of the close proximity between people and active vents, local scientists and government officials have to be ready to respond to the slightest changes in activity. An eruption that might be considered small or precursory in a different demographic context (like that of the Cascades or Alaska) could be life threatening in Indonesia.
3, Agriculture, Health, and Geochemistry (and etymology)
Ijen’s highly acidic waters attracts attention from specialists outside of the field of volcanology. Ijen has been studied intently by biologists, agriculturalists, and geochemists alike. Elements trapped in the lake water eventually make it downstream as water from Ijen drains through a dam towards a variety of agricultural fields below. Near the source, the river is known as Sungai Banyupahit (sungai=River, banyu=water, pahit=bitter), which indicates how noticeable the river’s chemistry is amongst the coffee plantations on the floor of the Ijen Caldera. By the time the river doglegs to the north and exits the caldera through a gap in the scarp, the water chemistry has been diluted by enough surface and ground water inputs that the name changes to Sungai Banyupuith (putih=white)—still suggestive of abnormal chemical concentrations but not nearly as potent.[*5]
The effect of downstream chemical concentrations has been seen to have several negative consequences in environmental and human health downstream. A series of academic studies showed that irrigation water from the Banyuputih River led to severe soil acidification in the Asembagus Plateau near the Java Sea. During a heightened period of gas release at Kawah Ijen from 1999-2001, a drastic decrease in downstream water pH correlated with a 90% decrease in rice yields from fields using acidic irrigation water (van Rotterdam-Los, 2008). Additionally, residents near the Java Sea claim that there is a notable increase in near-shore fish die-off when the Banyuputih River is not being used for irrigation (Delmelle and Bernard, 2000).
High levels of fluorine in well water are also correlated with reports of endemic dental and skeletal fluorosis amongst residents of the Asembagus area. Interestingly, measured fluorine concentrations in wells are technically within World Health Organization limits, but those limits are generalized world averages and are not calibrated for the amount of water consumption necessary to survive in a hot, tropical climate like that of Indonesia (Heikens et al., 2005b).
4, Tourism and Attraction
Despite the abundant attention from academics and professionals, Kawah Ijen is probably most widely known by the people who visit it leisurely. Hiking to Ijen is a fairly easy 3km walk from the ranger station at the base of Gunung Merapi. The trip affords beautiful views of the lake, and on a clear day, one can see Gunung Raung to the west (Figure G) and the island of Bali to the east.
Different times of day have advantages and disadvantages to hiking the crater. Some people like to try early morning and late evening for the cooler temperatures and the pleasure of refracted rays from the sun hovering near the horizon. Sunrise provides the best opportunity to get clear skies, but I prefer to go to Ijen in midday when entire crater and lake is fully exposed under the sun.
Though the hike is easy, the preceding car ride into the Ijen caldera is a rough trip. There is a northern and southern route, but neither is well maintained. It is possible to pass through the northern road in a low-clearance, 2WD van loaded with people (I’ve done it), but I would highly recommend hiring a Jeep to take you via the southern road.
The Jeep will cost you more time and money than the actual hike to the summit, so I suggest spending as much time at the crater as possible to make the journey worth it. There isn’t much to do up at the crater, but there are plenty of safe places away from cliffs and sulfur plumes if you wish to spend a longer amount of time at the site. There is also a small canteen and rest station 2/3 of the way up the trail that you can retreat to if you can’t find a comfortable spot at the crater. The canteen is also a rest post and weigh station for the sulfur miners, and I think (though I’m not sure) the canteen is run by the sulfur miners—meaning anything you buy is helping them out financially. Visitors that can speak Bahasa Indonesia will find that the sulfur miners, like most Indonesians, are friendly and open to chatting.
 The presence of a “Gunung Merapi” at Kawah Ijen is confusing (even for locals) considering that “Merapi” is also the name of a dangerous volcano just north of Jogjakarta around Central Java. “Merapi”
means “fire” in Malayu/Indonesian, thus many volcanoes take on the name Merapi. The Merapi of Jogjakarta is one of the most infamous in the world while the peak at Kawah Ijen is often forgotten or overlooked.
 Phreatic eruptions are those that are formed by relatively cool water coming into contact with hot magma; imagine the flash of steam after dropping water on a hot pan.
4] Volcanologists report eruption size with the Volcanic Explosivity Index (VEI). It is a logarithmic scale loosely related to erupted volume and plume height. Typical eruptions at Ijen and the Poás eruption from this video are VEI 1 events—events that happen on a daily basis around the world. Eyjafjallajökull, the eruption that disturbed air traffic across Europe in 2010, was a VEI 4 (1,000x larger than the Poás eruption). The 1980 Mount St. Helens eruption was a VEI 5 (10,000x larger than Poás).
 As a side note along the lines of local names, one has to wonder if Kawah Ijen’s potent chemistry is the inspiration for the name of the local regency. Kawah Ijen is located in Banyuwangi, which means “Fragrant Water.” The legendary source of the fragrance is a great battle in which the slain bodies of great warriors fell into and scented the local water.
Popular Media Resources
- Lane, M., 2011. Sulphur mining in a volcano. BBC. Available at: http://www.bbc.co.uk/news/world-asia-pacific-12301421 [Accessed February 10, 2011].
- Wong, E., 2010. In Java, Risking the Wrath of a Volcano. The New York Times. Available at: http://www.nytimes.com/2010/07/18/travel/18Explorer.html?_r=2&pagewanted=all [Accessed December 1, 2010].
- War Photographer Documentary about James Nachtwey
- Working Man’s Death Al Jazeera
Working Man’s Death Documentary webpage
Volcanology & Natural Science
Academic References in this Post
- Delmelle, P. & Bernard, A., 2000. Downstream composition changes of acidic volcanic waters discharged into the Banyupahit stream, Ijen caldera, Indonesia. Journal of Volcanology and Geothermal Research, 97(1-4), pp.55-75.
- Heikens, A., Sumarti, S., et al., 2005. The impact of the hyperacid Ijen Crater Lake: risks of excess fluoride to human health. Science of The Total Environment, 346(1-3), pp.56-69.
van Rotterdam-Los, A.M.D. et al., 2008. Impact of acid effluent from Kawah Ijen crater lake on irrigated agricultural soils: Soil chemical processes and plant uptake. Journal of Volcanology and Geothermal Research, 178(2), pp.287-296.