Natural Wonders: The Blue Fire of Kawah Ijen

Natural History
Blue lava flows from Kawah Ijen. Photo: Shutterstock

An electric blue fire cascading down a mountain slope suddenly lights the pitch blackness. This otherworldly site, the Kawah Ijen crater in Indonesia, is a geological masterpiece. It is part of the Ijen volcano complex in East Java, one of the world’s most highly sulfuric areas, dating back 300,000 years.

Photo: Shutterstock

Depending on conditions, sulfur takes on many colors. Its solid form is yellow and its liquid state is red. When sulphuric gases emerge and are exposed to surrounding high temperatures, the lava ignites the sulfur and the flames turn blue.

The temperatures at the Kawah Ijen crater can climb to an incredible 600˚C, but its blue flames are only visible at night. Sulfur combusts at only 360˚C, but a chemical reaction causes the blue hue, not the temperature itself.

The crater is also home to a small, greenish-blue lake full of hydrochloric acid. Over the years, hydrogen chloride gas spouted from the volcano and came into contact with the water to form the world’s largest hydrochloric acid lake. Its pH is a skin-scorching 0.5.

Chemical reactions at work. Photo: Shutterstock

Sulfur in solid form adjoins the lake, and massive deposits of solid yellow sulphur line the nearby hills after the sulphuric lava has cooled and solidified. It may be tempting to approach the lake, but the air is highly toxic. Visitors need proper respiratory equipment to proceed.

Heavenly to visit, hell to work in

The volcano has become well-known ever since it was featured in National Geographic. A documentary also highlighted the plight of Indonesian sulfur miners. They break up the solid sulfur and carry the large pieces either in baskets or on their backs. Their wage: about six cents per kilo. To carry their usual 100kg per day, they work into the night.

This labor has spurred controversy about exploitation, child labor, inadequate equipment, and health issues. Even though tourists use protective equipment, miners do not. They have reportedly acquired chest infections and lung diseases from the ongoing exposure to the toxic air. Their industry has little to no regulation.

Other volcanoes around the world, such as Vesuvius and Kilauea, have reportedly emitted blue lava, but not as consistently as Ijen. You wouldn’t want to work there, but to see it briefly is a wonder.


About the Author

Kristine De Abreu

Kristine De Abreu

Kristine De Abreu is a writer (and occasional photographer) based in sunny Trinidad and Tobago.

Since graduating from the University of Leicester with a BA in English and History, she has pursued a full-time writing career, exploring multiple niches before settling on travel and exploration. While studying for an additional diploma in travel journalism with the British College of Journalism, she began writing for ExWeb.

Currently, she works at a travel magazine in Trinidad as an editorial assistant and is also ExWeb's Weird Wonder Woman, reporting on the world's natural oddities as well as general stories from the world of exploration.

Although she isn't a climber (yet!), she hikes in the bush, has been known to make friends with iguanas and quote the Lord of the Rings trilogy from start to finish.

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7 months ago

After reading this it’s impossible to not associate this with child labor and exploitation, mark this off my bucket list.

Craig Quigley
Craig Quigley
7 months ago
Reply to  jmaf

Your logic makes no sense. Whether you visit or not, will have no effect on the sulphur mining – in fact i suppose more tourism creates more jobs away from backbreaking work in mines etc