ABOUT IJEN

The formation of Ijen Plateau and Ijen crater lake

Indonesia is famous for hosting some of the world's most powerful volcanoes. Ijen crater lake is the most amazing Indonesian lake, representing a solution of sulphuric acid and hydrogen chloride, the most powerful existing acids. The lake contains 600,000 tonnes of hydrogen chloride, 550,000 tonnes of sulphuric acid, 200,000 tonnes of aluminium sulphate and 170,000 tonnes of iron sulphate, with an acidity around pH 0.5. Any eruption through this lake would expel the water and create deadly mudflow that can claim hundreds of lives and properties. Pre- and post-caldera activity of Ijen Pre-caldera activity of the Ijen crater complex is supposed to have started prior to 300,000 years ago. It probably formed a large single stratovolcano - Old Ijen - with an estimated altitude of 3500 m. The caldera formation is associated with the eruption of a large volume – around 80 cubic kilometres - of pyroclastic flow deposits. These are waves that consist of solid or semi-liquid lava, gas, rocks and ash. They can reach temperatures up to about 850 °C and can reach a speed to around 725 km/h. The event occurred some time before 50,000 years ago. This is based on analysis of a lava flow of Mt. Blau. Mt. Blau is considered to be the oldest post-caldera unit. Post caldera activity produced the rim cones and the inner cones. These younger volcanoes produced the ash and scoria cones, lava flows, pyroclastic flow and surge deposits and debris avalanche material that now cover the caldera flow. Ijen's landscape full of volcanic cones The Ijen Plateau was at one time a huge active crater complex of 134 square kilometres in area. Nowadays, the large caldera complex hosts a large number of volcanic edifices of which Ijen and Raung are the most active. The Ijen caldera has a diameter of about 14-16 km. The landscape is dominated by the volcanic cones of Ijen (2368 m) and Merapi (2800 m) on the north-eastern edge of the plateau, and Raung (3332 m) on the south-western corner. The Ijen crater stands inside the caldera, while Merapi and Raung have arisen along a ring fracture at the edge of the caldera. The caldera’s northern margin is clearly visible as a typical caldera escarpment with a steep inner slope and elevations ranging from 850 to 1559 m. The southern and eastern walls are covered by the marginal volcanoes of Suket (2950 m), Jampit/Pendil (2338 m), Rante (2644 m), Merapi (2799 m), Ijen (2386 m), Pawenen (2123 m) and Ringgih (1965 m). Inside the caldera the topography is dominated by a large number of extinct volcanic cones: Cilik (1872 m), Pendil (2375 m), Anyar (1276 ), Genteng (1712 m), Gelaman (1726 m), Kukusan (1994 m), Papak (2099 m), idodaren (2100 m), Blau (1774 m), Gendingwaluh (1519 m), Lingker (1630 m) and Kunci (1788 m). Eruptions over time Ijen is especially interesting because of a relationship seen between lake level and eruptive activity. On several occasions when the lake level has been lowered by artificial means, fumarolic activity under the lake has increased, lake temperature has risen, and sometimes hydrothermal or phreatic eruptions have occurred. These phenomena are thought to result from reduced pressure resulting from lowering the lake level. The historical record of volcanic activity at Ijen dates back to 1586, and includes dozens of eruptions. Eruptions of Ijen are associated with increases in seismic activity and in the temperature of the crater lake. In 1817 the crater lake in Kawah Ijen collapsed, producing mudflows that engulfed three villages and killed an unknown number of people. In 1917 water from the lake flowed over after a large tectonic earthquake near Bali. The following month water in the lake was spouting some 9 m into the air in a muddy, noisy display. The temperature of the lake rose to scalding intensities in March but dropped back to lukewarm levels by late 1917. The lake heated up again in 1921, with steaming gases above the water surface until 1923. In 1936 an eruption similar to that of 1817 was recorded. In 1952 Ijen erupted after several strong local earthquakes. The volcano spewed ash up to 1000 meters altitude in the air. An eruption cloud appeared, and boiling activity was observed in the lake. In 1962, 1976 and 1991 bubbling water was recorded, with changing of water colour. In 1993 an explosive volcanic eruption was recorded in which steam and tephra was released. In 1997 there was increased seismic activity recorded. The colour of the lake changed, gas bubbles were seen and there was a strong sulphuric odour; birds were seen falling into the water. The last eruption was recorded in 1999.