In East Java, Indonesia, an explorer once paddled a rubber dinghy across a turquoise crater lake so corrosive its pH measured 0.13, stronger than battery acid. This is Kawah Ijen, home to the world’s largest highly acidic crater lake and a volcanic complex that behaves like a different planet. Magma constantly degasses sulfur dioxide and hydrogen chloride, creating a continuously regenerating reservoir of sulfuric and hydrochloric acid that dissolves metals and gives the water its deceptively beautiful color.

At night the volcano emits towering electric blue flames as pressurized sulfuric gas auto-ignites at temperatures up to 600 degrees Celsius. Yet Ijen is also one of the most grueling sulfur mining operations on Earth. Local miners channel the gas through ceramic pipes to condense molten sulfur, then haul 75 to 90 kilogram loads up a steep crater and miles down the mountain, twice a day, for roughly thirteen dollars. We examine the collision of natural wonder, lethal danger, and economic necessity.

• Why a pH of 0.13 makes the lake stronger than stomach or battery acid
• How fumaroles auto-ignite sulfuric gas into the rare blue fire phenomenon
• The chemistry behind sulfur turning from blood red liquid to vibrant yellow solid
• The brutal economics keeping roughly 200 miners working amid toxic fumes
• How photojournalist James Nachtwey was incapacitated while miners walked past