Ijen (earlier spelled “Idjen”) is the name of a volcanic complex in Jawa Timur , the easternmost province of the Indonesian island of Java . Best known in this vast complex, the base diameter of 75 km shall be enclosed by bare walls of the crater lake Kawah Ijen, which is by some geologists and mineralogists referred to as “the biggest acid vat in the world.” With its acidic turquoise waters and its violent steaming solfataras he is indeed impressive, but for safety reasons are not always freely accessible tourist destination. Another frequent site of volcanic activity is the Gunung Raung, which is perpendicular to the inside sloping crater of a volcano crater in the deepest of the earth.
From an original, probably in the Upper Pleistocene been estimated incurred twin volcano, the height to 4000 m, remained after the collapse of an elliptical caldera left, which is of a diameter of up to 16 kilometers one of the largest calderas of the earth. About 80 cubic kilometers of ash and rock were ejected from this collapse, they form a 100 to 150 m thick layer is deposited mainly on the outer slopes of the northern caldera.
Subsequent volcanic activity has resulted in this caldera is only partially available. Almost completely preserved is the northern semi-circular Calder Arand, which up to 1717 m high Kendeng Mountains, through the middle of the Banyuputih-flow, a difficult to access, some over 500 m deep gorge has been excavated to the north and the northern half of the caldera, the of about 900 m to 1500 m to the south rising Ijen Highlands. The deepest part of the high plateau lies at 850 meters above sea level, near the village of Blawan.
The crater of Gunung Ijen shows large morphological differences between the western and eastern parts. In the West, the ribs extend to the outer slopes of the volcano up to the rim of the crater, which has accelerated the erosion of the western boundary. In the north, east and south of the border ribs below the crater rim, which thus has a much higher stability and represents a well-preserved, almost equally high rampart round. In addition, there was the western part of products that the erosive forces could afford little resistance. The eastern part consists of solid material on the other hand is also supported by two older crater walls and the neighboring Mount Merapi.
This has led to the western rim of the crater has been largely destroyed and the overflow of Crater Lake is located here. The destruction of this margin was not only due to erosion, but also by a lava flow that is further down in many places been preserved, and phreatic eruptions that have ejected the crater lake. The resulting mudflows (lahars) have deepened the breach in the western edge and reduces the level of the surface of the newly formed lake on the current altitude of 2148 m above sea level. Are still clearly the traces of lahars in 1817 to recognize that along the Banyupahit, the upper reaches of the Banyuputih the Ijen Plateau flooded, rushing through the gorge of the Banyuputih the north rim of the caldera in the coastal plain and east of the city Asembagus fan out like a delta flowed into the sea.
The Ijen crater embedded in Kawah Ijen lake is 960 m long, 600 m wide and up to 200 m deep. Its surface is 41 hectares. Significant correlations exist between the different amounts of precipitation, the level of the lake level and water temperature. Between the dry season from May to October and the wet season from November to April the level of the lake level varies by up to four meters. Consequently, the volume of the lake varies from 32 million to about 36 million cubic meters. The intense blue-green color of the Kawah Ijen is caused by its high content of alum , sulfur and gypsum . The Alaungehalt is estimated at over 100,000 tons. The water of this lake extremely acid reacts: analyzes in 2005 and 2006, the lake has a pH below 0.3, established in drain Banyupahit 0.4 to 0.5. Inflows increase the water with a neutral pH to a breakthrough in the north of the Calder Banyuputih Arand, depending on water levels at 3.0 to 3.5.
The temperature of the seawater is highly variable, with a long-term upward trend has been observed. In October 2000, 32 ° C, measured in the years to 35 ° C to 45 ° C. The highest value is 48.1 ° C, measured on 13 July 2004 (November 2007). Almost always, develop steam clouds on the lake because the water temperature is higher than the air temperature.
On the southeastern shore of the lake is one of the most active solfataras the earth, with 190 to 240 ° C hot fumaroles has deposited the important sulfur accumulation in Indonesia with up to 8 meters thick sulfur banks. In the year 1968 saw the official opening instead of a sulfur mine. Sulfur vapors through an elaborate system of about 10 m long and 50 cm thick pipes led to deeper outlets, where the sulfur hot as 110 to 120 ° C viscous orange to red-colored mass comes to light, and after cooling turns yellow to a bright . Workers from the local population with iron bars to break up the sulfur, the broken pieces stacked in two bamboo baskets and carry them over the 150 m above the crater rim to the valley. Overheating of the sulfur ignites occasionally even as a light blue and flows into the lake of burning power, particularly its luminosity in the dark of night has a mystical-sounding show.
Formerly flowed after heavy rainfall the acidic waters of the Kawah Ijen about the breach in the western rim of the crater, was united on the Ijen Plateau with tributaries of the Banyupahit, flowed with the Banyuputih through the gorge in northern Calder Arand and directed major damage in the rice fields and sugar plantations passed to the northern coastal plain. In 1921 it was in the overflow of Kawah Ijen built a lock that prevents unauthorized outflow of acidic water. The walls of the lock consists of sulfur blocks as other materials do not withstand the acidic water. In addition, all were provided with irrigation Banyuputih derivatives of the locks. If the lake level is critically low, the floodgates of Banyuputih be closed. In the event of a major phreatic eruption, however, these protective measures are ineffective: The lahars flowed down in November 1936 could not hold the lock on Kawah Ijen. The source of the outflow of Kawah Ijen, the Banyupahit located down the valley below the sluice, where has the acidic waters of the lake through the ashes of the volcano opened a shell underground flow.