A Lake of Battery Acid
The turquoise water of Kawah Ijen, located in East Java, is the largest highly acidic crater lake on Earth. This body of water has a volume of about 36 million cubic meters and fills a crater that is roughly 722 meters in diameter and 200 meters deep. The extreme acidity is due to a potent mixture of hydrochloric and sulfuric acids, with pH values measured as low as 0.5 at the edges and 0.13 in the middle, comparable to the strength of car battery acid. The water temperature hovers around 60 degrees Celsius (140 degrees Fahrenheit), heated by the magma chamber deep beneath the lake bed.
The lake's startling color is a result of its unique chemistry, specifically the high concentration of dissolved metals. Its hyperacidity originates from volcanic gases, like sulfur dioxide and hydrogen chloride, that emanate from fumaroles and dissolve into the water. This process creates a chemical environment so corrosive it can dissolve metal and cause severe skin irritation on contact. The acidic, metal-rich water flows out of the crater to form the Banyupahit River, which significantly impacts downstream ecosystems and is used by local farmers for irrigation, despite having a pH between 2.5 and 3.5. While the lake's water column itself is considered too extreme for most life, studies have found archaea and other extremophile microbes in the river system originating from it, showing life's ability to persist in harsh conditions.
The Phantom Blue Fire
At night, Kawah Ijen displays a rare natural phenomenon: an electric-blue fire. The blue glow is not lava. The blue glow is the light produced by the combustion of sulfuric gases that escape from cracks in the rock at high pressure and temperatures up to 600°C (1,112°F). When these gases meet the oxygen-rich atmosphere, they ignite, creating flames that can reach up to five meters high. Some of the gas condenses into molten sulfur, which pools on the ground and continues to burn with the same eerie blue light, creating the illusion of flowing blue lava. This spectacle is only visible in darkness, bringing visitors for pre-dawn hikes.
This same sulfur supports a labor-intensive mining operation that has existed for centuries. Miners descend into the crater, often with minimal protective equipment, to harvest the solidified sulfur. Volcanic gases are channeled through a network of ceramic pipes, which causes the molten sulfur to condense and pour out, cooling into bright yellow deposits. Workers break off chunks of this sulfur and carry it out of the crater in baskets weighing between 75 and 90 kilograms. The journey involves a steep 300-meter climb up the crater wall, followed by a three-kilometer trek down the mountain. Many miners make this arduous trip twice a day, earning around $13 USD for their efforts.