The Ijen volcano complex is a group of stratovolcanoes, in
East Java, Indonesia. It is inside a larger caldera Ijen,
which is about 20 kilometers wide. The Gunung Merapi
stratovolcano 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.
In 2008, explorer George Kourounis took a small rubber
boat out onto the acid lake to measure its acidity. The pH
of the sulfuric acid in the crater was measured to be 0.5.
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 September 2010 the typical daily earnings
were equivalent to approximately $13.00 US. The miners often
use insufficient protection while working around the volcano
and are susceptible to numerous respiratory complaints.
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