The incredible natural phenomena are found on Mount Ijen, which is an active volcano crater located in East Java, Indonesia. “Kawah Ijen” directly translates to “lonely crater” and is a small lake with two unusual occurrences in nature.

First, this lake exhibits an active solfatara that emits hot, flammable sulfurous gases. This looks like a white mist that flows out of the edges of the lake. These light up as they mix with Earth’s air and burn with an electric blue flame. Some of the gas condenses in order to produce flows of substance that will burn with an electric blue flame. The flames are difficult to see during the day but illuminate the landscape at night.

Secondly, Kawah Ijen Lake glows with a bizarre, yet beautiful, cyan color. The color of the water is a result of its extreme acidity and high concentration of dissolved metals. It is the world’s largest highly acidic lake with a measured pH as low as 0.5.

This is obviously an amazing sight to see, but is it safe? Mount Ijen is generally safe to visit, but if you have asthma or any kind of breathing/health problems, you should skip the blue flame and just enjoy the lake from above. The sulfurous gases can trigger your lungs or other parts of your body and cause a bad reaction.

Even if you don’t have any health conditions, it’s important to remember that the lake is not 100% safe. Eruptions at Mount Ijen don’t seem to be very common but they can happen. 49 Indonesian sulfur workers were killed in a gas explosion in 1976, and another 25 died in 1989. More recently, 30 local people were hospitalized by toxic gas after a small eruption in 2018, and a sulfur worker drowned in a 3-meter tsunami from the lake in 2020.

Overall, you should definitely visit this lake as it is a spectacular experience, but be mindful of your safety.