Natural Wonders: The Blue Fire of Kawah Ijen

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.