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The Ijen volcano complex is a group of stratovolcanoes inside a larger caldera Ijen, which is about 20 kilometers wide. The Gunung Merapi stratovolcano (not to be confused with Central Java's Gunung Merapi) is the highest point of that complex. West of Gunung Merapi is the Ijen volcano, which has a one-kilometer-wide turquoise-colored acid crater lake. The lake is the site of a labor-intensive sulfur mining operation, in which sulfur-laden baskets are carried by hand 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. The active crater at Kawah Ijen has an equivalent radius of 361 meters, a surface of 41 × 106 square meters. It is 200 meters deep and has a volume of 36 × 106 cubic meters.
Sulfur mining at Ijen
An active vent at the edge of the lake is a source of elemental sulfur, and supports a mining operation. Escaping volcanic gasses are channeled through a network of ceramic pipes, resulting in condensation of molten sulfur. The sulfur, which is deep red in color when molten, pours slowly from the ends of these pipes and pools on the ground, turning bright yellow as it cools. The cooled material is broken into large pieces and carried out in baskets by the miners. Typical loads range from 70–100 kilograms, and must be carried to the crater rim approximately 200 meters above before being carried several kilometers down the mountain. Most miners make this journey twice a day. The miners are paid by a nearby sugar refinery by the weight of sulfur transported; as of July 2005 the typical daily earnings were equivalent to approximately $5.00 US. The miners often use insufficient protection while working around the volcano and are susceptible to numerous respiratory complaints. Their life expectancy is only about 30 years.
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