Ijen Crater is the biggest crater lake in Java. The sulfur crater lake lies between a natural dams of deeply etched rock. It is 200 meters deep and contains about 36million cubic meters of steaming acid water, shrouded in a smelling swirling sulfur cloud. Inside the crater the different color and size of stones are found. Indeed the crater of Ijen is beautiful garden of stone as well.
The view of sulfur miners who climb and go down to the crater is also amazing. A man puts about 10 kg of yellowish stone in to his basket, before he descends the mountain slope to sell his load, carrying the same basket, going in the same direction, digging the same mineral. It is the natural picture that can be seen everyday.Ijen Plateau lies in the centre of Ijen-Merapi Malang Reserve, which extends over much of the mountainous region directly west of Banyuwangi and borders on the Baluran National Park in the northeast. As at Mt. Bromo, the caldera is best viewed from the air. Fortunately, almost all commercial flights operating between Denpasar - Surabaya, Yogyakarta or Jakarta usually fly, if not directly over, then close by Ijen plateau, where the seemingly luminous blue/green crater lake forms an unmistakable landmark. It is beautiful scenery and located about 32 km to the north west of Banyuwangi. The principal attraction at Ijen is the large Crater Lake that has much sulfur, which lies hidden between sheer walls of deeply furrowed rock at more than 200 meters. The Ijen crater itself lies at approximately 2,300 meters above sea level. It forms a twin volcano with the now extinct Mount Merapi. The enormous Crater Lake, which is 200 meters deep and covers an area of more than meters, a million square meters, contains about 36 million cubic meters of steaming, acid water.
The crater can be reached from either the east or the west by any kinds of vehicles, but the second part of the trip covers distance 3 km on foot (jungle track). However, the latter is more popular approach, since the climb from the road's end to the edge of the lake is only one and a half hours. And a walk around the lake takes a full day.The temperature drops at night, near the crater rim it can fall to about 5° Celsius. The road ends at Jampit, where very basic shelter is available. It is also possible to sleep in the old vulcanology station further up the hill, now used by sulfur collectors, but permission must be obtained in advance.
The sulfur is transported entirely on foot. In the past, horses were used but they were found to be less practical on the hazardous terrain. Today, the mine yields nine to twelve tons of sulfur per day.Men carry individual loads of up to 70 kg, often barefooted, up to the rim of crater and then 17 km down the mountainside to a factory near Banyuwangi. The porters are paid by weight. The most important advice if you are traveling to Ijen is: "If you lose your way, just look out for the sulfur trail". The meaning was clear, since a continuous flow of two ways traffic, carrying the sulfur down the mountainside from the lake and trudging up again to re-load, had left a yellow trail on the well-worn path. The best time for seeing Ijen Crater is at 8 am. to 9 am.
Blue Flames and a Blue Acid Lake at Ijen crater , on the island of Indonesia has two of the most unusual occurrences on Earth. The first is an active solfatara that emits hot, flammable sulfurous gases. These ignite as they enter Earth's oxygen-rich atmosphere and burn with an electric blue flame. Some of the gas condenses in the atmosphere to produce flows of molten sulfur that also burn with an electric blue flame. The flames are difficult to see during the day but illuminate the landscape at night.
The second occurrence is a one-kilometer-wide caldera lake filled with turquoise blue water. The color of the water is a result of its extreme acidity and a high concentration of dissolved metals. It is the world's largest highly acidic lake with a measured pH as low as 0.5. The cause of its acidity is an inflow of hydrothermal waters charged with gases from a hot magma chamber below. The best time for seeing Blue Flame at Ijen Crater is at 2 am. to 4 am.