Ijen Crater volcano complex at the eastern end of Java consists of a group of small strato volcanoes constructed within the large 20-km-wide Ijen (Kendeng) caldera. The north caldera wall forms a prominent arcuate ridge, but elsewhere the caldera rim is buried by post-caldera volcanoes, including Gunung Merapi stratovolcano, which forms the 2799 m high point of the Ijen complex. Immediately west of Gunung Merapi is the renowned historically active Kawah Ijen volcano, which contains a nearly 1-km-wide, turquoise-colored, acid crater lake. Picturesque 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.
Interestingly, Sulfur is mined at the lake’s edge and the strong odor of this is not for those with a tender stomach. The people who work in these sulfur mines are well versed in their job. They carry the sulfur up to the top of the crater and afterwards walk the 19 km down the mountain to Banyuwangi where at a factory the sulfur is treated. These guys can carry as much as 80 kilos of the foul smelling material!.
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.