Kawah Ijen is the Indonesian volcanic site famous for blue flames and sulfur miners seen at night.
Ijen is a volcanic complex in East Java, and its crater contains Kawah Ijen, a highly acidic lake. The blue appearance is caused by sulfur gases emerging through fractures and burning at high temperatures; the flames are not blue lava.
Miners collect solid sulfur near the crater and carry heavy loads along steep paths. The area’s striking colors and industrial activity have made it a well-known destination, but the gases and acidic lake create serious hazards.
Mount Bromo is another celebrated East Javanese volcano, while Kelimutu is known for its colored crater lakes. Those volcanoes are not the site usually associated with Ijen’s nighttime sulfur flames.