Kawah Ijen is a group of stratovolcanoes in Banyuwangi Regency, Indonesia, in eastern Java, within a larger Ijen caldera, which is about 20 kilometers wide.
The crater lake on the top is recognized as the largest acid lake in the world.
It is also a source for the Banyupahit River, resulting in very acidic and metal-enriched river water which has a significant negative effect on the ecosystem of the valley. The caldera is a circular depression formed following a violent eruption.
Explorer George Kourounis took a small dinghy on the acid lake to measure its acidity. The pH of the water in the crater was measured at 0.5, attributed to the presence of sulfuric acid. In fact, other sources attribute the acidity to hydrochloric acid, or to a complex of acids and minerals.
A two hour hike is required to reach the crater rim, followed by a 45 minute walk to the crater shore. The blue fire ignites for the sulfuric gas, which emerges from the cracks with temperatures up to 600 ° C. Blue flames also form above the lava, which appears red by day and bright blue at night.
Passionate about volcanology Martin Rietze, documented the spectacular phenomenon. The Indonesian volcano Kawah Ijen, east of Java, erupts intense red lava by day, while at night it changes color and becomes phosphorescent blue, complete with very high flames.
Martin Rietze: "People should never face these dangers"
According to another interpretation, this is due to the high amount of sulfur present both in the composition of the lava itself and on the outside. Once the liquid sulfur passes through the volcanic vents to the surface, it gives off a gas that is potentially deadly to humans.
Rietze said: "People should never approach an active crater without first knowing the potential dangers." Going to the Kawah Ijen crater is certainly possible but for safety reasons it is advisable to bring gas masks and other specific protections with you.
To reach the crater, located at about 2,883 m above sea level, a two-hour trek is planned.
Since numerous photo shoots have immortalized the ghostly blue flames of the Kawah Ijen, the number of tourists visiting the area each year has soared.