The most amazing Indonesian volcano is Ijen Crater or 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.

kawah ijen, ijen crater, ijen volcano, ijen plateau

On the edges of the lake, the fumaroles (volcanic gas eruptions) depose 4 tonnes of sulfur daily. 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.sulfur miner at kawah ijen

Kawah Ijen is the world's largest highly acidic lake and is the site of a labor-intensive sulfur mining operation in which sulfur-laden baskets are hand-carried from the crater floor.

Many other post-caldera cones and craters are located within the caldera or along its rim. The largest concentration of post-caldera cones forms an E-W-trending zone across the southern side of the caldera. Coffee plantations cover much of the Ijen caldera floor, and tourists are drawn to its waterfalls, hot springs, and dramatic volcanic scenery.

The walls of the Kawah Ijen 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 12ca0o C, like bright red trails, which gradually solidify, turning lemon yellow. The lake contains 600,000 tonnes of hydrogen chloride, 550,000 tonnes of sulfuric acid, 200,000 tonnes of aluminium sulphate and 170,000 tonnes of iron sulphate.
ijen lake
People from the neighboring area extract sulfur from the crater manually. Each worker can transport 40 to 70kg (90 to 155 pounds) at once on the abrupt slopes of the volcano, using bamboo ladders where the slope is too steep. In one day, a man can carry up to 360 kg (750 pounds) of sulfur. The daily production of the exploitation is just of 4 tonnes, a derisory quantity, if we consider the fact that the crater harbors 30,000 tonnes of sulfur. Industrial exploitation of the lake has not been planned so far, as the volcano erupts from time to time, projecting acid to the height of 600 m (2,000 ft) and splashing the neighboring areas with a corrosive rain.