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Kawah Ijen

The blue fire of Kawah Ijen, Indonesia
The blue fire of Kawah Ijen / Dodi Mulyana, Flickr / CC BY 2.0

WorldBlue  In short

One of the most unusual volcanoes on the world is Kawah Ijen. It contains the largest lake of acid in the world but especially impressive are the eerie blue flames around the solfataras in the crater – an unforgettable sight in the night.

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GPS coordinates
8.0581 S 114.2424 E
Location, address
Asia, Indonesia, East Java, Banyuwangi and Bondowoso Regencies
2,154 m (level of crater lake)
Alternate names
Idjen, Kawah Ijen (Ijen crater)

Map of the site

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WorldYellow In detail


There is Ijen and Kawah Ijen. The first – Ijen (also Kendeng) – is the whole complex of volcanoes in this area, spread around the giant, approximately 20 km wide caldera. The highest volcano here is the 2,799 m tall Gunung Merapi. But the story goes about another part of Ijen: a crater that is located to the west of the mighty Gunung Merapi – Kawah Ijen (Ijen crater).

The lake of acid in Ijen Crater, Indonesia
The lake of acid in Ijen Crater / © CEphoto, Uwe Aranas, Wikimedia Commons

This crater has several very unusual characteristics, including an enormous lake of pure acid and… cracks that emit burning gas which in the night glow in eerie blue color. But, when the day comes, a group of men arrives to hack off large chunks of pure, yellow sulfur which constantly is emanating from the ground.

Lake of acid

When looking at the satellite image, Kawah Ijen attracts attention with a lake in unnatural, turquoise color. This crater lake is filled with almost pure sulphuric acid and is the largest highly acidic lake in the world. Lake is some 0.7 by 0.9 km large, it contains some 30 million m³ of acidic liquid (hyper acidic brine), and is some 200 m deep.

The lake of acid in Ijen Crater, Indonesia
The lake of acid in Ijen Crater / Berry, Flickr / CC BY-SA 2.0

Adventurer George Kourounis in 2008 in a rubber boat measured the acidity of the lake: at the edges, the acidity was 0.5 pH, and in the middle – 0.13 pH. Thus it is a lot more acidic than the acid in car batteries.

From the lake starts a river – Banyu Pahit. Of course, this also is a very unusual river with highly acidic water. In this water have been dissolved metals – thus it is a natural source of chemical pollution.

In the case of a powerful eruption the wave of acid from the lake would create a potential danger to surrounding villages.

Sulphur mining

At the south-eastern bank of the lake are located fumaroles that emit sulfurous gases. Over time here have formed rich deposits of this yellow substance.

Sulphur miner in Ijen Crater, Indonesia
Sulphur miner in Ijen Crater / Jean-Marie Hullot, Wikimedia Commons / CC BY-SA 2.0

People have installed a system of ceramic pipes and molten sulfur flows through these pipes and accumulates in heaps on the ground.

Some 200 local miners are mining the sulfur – some 14 tons per day. This extremely hard work is done with hand tools. Chunks of sulfur are carried away on the back. Each miner carries some 70 – 90 kg of sulfur several times per day. The work is hazardous for the health, especially for the respiratory system and teeth – but working with gas masks is not easy either, thus workers often prefer to work without them.

Blue fire

The sulfurous gas and condensed liquid in some locations are burning. During the daytime, the flames are not that bright but at the night the sight is unforgettable – the flames have a deep blue color. For the most part, the flames are ignited by people – by torches of sulfur miners who often work also during the nighttime.

The blue fire of Kawah Ijen
The blue fire of Kawah Ijen./ Thomas Fuhrmann, Wikimedia Commons / CC BY-SA 4.0

These flames are up to 5 m high and the temperature of the flame reaches up to 600° C. Part of the gas is condensed as a liquid which continues to burn.

Some other volcanoes around the world also have such blue fires but the Blue Fire of Ijen is by far the largest in the world.

Nighttime ascent on this mountain is an increasingly popular tourist attraction and few regret the effort – the sight is truly unforgettable. Though one should be very careful here because this is a very hostile environment for any form of life. Of course, the assistance of local guides is of high value, thus also giving some input into the economy of the hospitable, hard-working local people.


  1. Global Volcanism Program, Ijen. Accessed on February 4, 2017

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The lake of acid in Ijen Crater / © CEphoto, Uwe Aranas, Wikimedia Commons

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