Ijen crater

The most amazing Indonesian volcano is Kawah Ijen (2,600m or 8,660ft tall), the "Green Crater" from Eastern Java, which has a lake made of 36 million cubic meters representing a solution of sulfuric acid and hydrogen chloride, the most powerful existing acids.

On the edges of the lake, the fumaroles (volcanic gas eruptions) depose 4 tonnes of sulfur daily. Such acid lakes are also found on the volcanoes Kusatsu-Shirane (Japan) and Poas (Costa Rica), but the Indonesian lake is by far the largest acid lake on Earth, having a maximum depth of 212m (706ft). These lakes result from the mix of rainfall water with gases coming from the depths of the volcano.

The walls of the Kawah Idjen lake are light ocher, but the water has a turquoise color, with emerald reflexes. The temperature of the water is of 34o C, and sulfur bubbles float on the surface. The surroundings are covered by a sulfur powder. The smell is pungent and irritating, filled with sulfur dioxide. From place to place, sulfur pours at a temperature of 120o C, like bright red trails, which gradually solidify, turning lemon yellow.