Kawah Ijen

Kawah Ijen’s famous “blue lava” isn’t molten rock glowing blue, but rather the combustion of sulfuric gases emitted from its volcanic vents.

These gases, rich in elemental sulfur and sulfur dioxide, ignite when exposed to air temperatures above 360°C, producing a brilliant blue flame.

When the burning sulfur condenses, it forms solid sulfur deposits around the crater.

The volcano's emissions often include trace elements like selenium and arsenic, common in high-temperature fumaroles.

The vivid glow occurs mostly at night, as the flames are otherwise invisible in daylight, and the phenomenon highlights the volcano’s intense geochemical activity tied to subduction-related magmatism.