The Ijen volcano complex at the eastern end of Java consists of a group of small stratovolcanoes constructed within the large 20-km-wide Ijen (Kendeng) caldera. The north caldera wall forms a prominent arcuate ridge, but elsewhere the caldera rim is buried by post-caldera volcanoes, including Gunung Merapi stratovolcano, which forms the high point of the complex. Immediately west of the summit (Gunung Merapi) is the historically active Kawah Ijen crater, which contains a nearly 1-km-wide, turquoise-colored, acid lake. Picturesque Kawah Ijen is the world’s largest highly acidic lake and is the site of a labor-intensive sulfur mining operation in which sulfur-laden baskets are hand-carried 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. Coffee plantations cover much of the caldera floor, and tourists are drawn to its waterfalls, hot springs, and dramatic volcanic scenery.
It is inside a larger caldera Ijen, which is about 20 kilometres wide. The Gunung Merapi stratovolcano is the highest point of that complex. The name “Gunung Merapi” means “mountain of fire” in the Indonesian language (api being “fire”); Mount Merapi in central Java and Marapi in Sumatra have the same etymology.
West of Gunung Merapi is the Ijen volcano, which has a one-kilometre-wide turquoise-coloured acidic crater lake. Many other post-caldera cones and craters are located within the caldera or along its rim. The largest concentration of post-caldera cones run east-west across the southern side of the caldera. The active crater at Kawah Ijen has a diameter of 722 metres (2,369 ft) and a surface area of 0.41 square kilometres (0.16 sq mi). It is 200 metres (660 ft) deep and has a volume of 36 cubic hectometres (29,000 acre·ft).
The lake is recognised as the largest highly acidic crater lake in the world. It is also a source for the river Banyupahit, resulting in highly acidic and metal-enriched river water which has a significant detrimental effect on the downstream river ecosystem. In 2008, explorer George Kourounis took a small rubber boat out onto the acid lake to measure its acidity. The pH of the water in the crater was measured to be 0.5 due to sulfuric acid.
About 300,000 years ago, volcanic activity in this area began building a large stratovolcano that is called “Old Ijen” today. Over thousands of years and repeated eruptions, it grew to an elevation of about 10,000 feet. Lava flows and pyroclastic deposits from Old Ijen disconformably overly the Miocene limestone.
Then, about 50,000 years ago, a series of enormous explosive eruptions produced a caldera about ten miles in diameter. About twenty cubic miles of material was ejected and covered the surrounding landscape up to 300 to 500 feet deep in ejecta and volcanic ash.
In the past 50,000 years, many small stratovolcanoes have formed within Old Ijen’s caldera and covered its southern and eastern margins. Kawah Ijen covers part of the eastern margin. Thousands of years of weathering have converted the pyroclastic deposits into rich, fertile soils which now support coffee plantations.
The volcano remains active. The last magmatic eruption occurred in 1817. Phreatic eruptions occurred in 1796, 1917, 1936, 1950, 1952, 1993, 1994, 1999, 2000, 2001, and 2002. These have caused very little damage but present a danger to anyone mining sulfur or visiting the caldera.
Mount Ijen Volcanic Complex
Overview map illustrating the Ijen volcanic complex located in Eastern Java. The large sub-circular shape indicates the margin of the Ijen caldera. The active Kawah Ijen cone is in the East part of the caldera. The solid and dashed line segments respectively discriminate between the well constrained North topographic margin (“Kendeng caldera wall”) and the inferred South margin. Associated volcanic centers reside both inside the caldera (lightly shaded triangles), and on the rim (solid black triangles). In this interpretation of the caldera, it is about 13 km wide. The caldera drains to the North in a river system that starts at the outflow from the crater lake. The major river is called Banyu Pahit (also spelled Banyuputhih). Raung and Suket cones sit West of and outside the Ijen complex. (From van Hinsberg and others (2010)).
Map of the Ijen complex showing hazard zones (Yellow–Zone I; Pink–Zone II, and Red–Zone III; as described in the legend at right). For scale, a small (rather faint) inner red dashed ring around Kawah Ijen crater and the lake it encloses has a diameter of 1.5 km; the pink dashed ring, 6 km, and the outer yellow ring, 8 km. The lake’s surface is at 2,200 m elevation. Note location of observation posts. The large urban area on the N coast has a population of 1.5 million and is here labeled Trigonco (but other local names apply, as seen in figure 15). Map extracted from an original prepared by Mulyana, A.R., Effendi, W., Karim, A., and Rukada, T. (2006). (Courtesy of CVGHM and VDAP).
Largest Blue Flame Area in The World, Mount Ijen Crater
Since National Geographic mentioned the electric-blue flame of Ijen, tourist numbers increased. The phenomenon has occurred for a long time, but beforehand there was no midnight hiking. A two-hour hike is required to reach the rim of the crater, followed by a 45-minute hike down to the bank of the crater. The blue fire is ignited sulphuric gas, which emerges from cracks at temperatures up to 600 degrees Celsius (1,112 degrees Fahrenheit). The 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 World’s Largest Acidic Lake
The about 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.
Given the recent concerns about activity in Kawah Ijen’s crater lake, a simple model of the shallow crust in this area provides a way to help visualize conditions and processes in the subsurface. A simplified model of the environment and subsurface associated with Kawah Ijen’s crater lake. This illustrates some of the factors associated with the lake’s chemistry, including rainfall, runoff, surface-rock weathering, and the interconnected hydrothermal, geochemical, and magmatic systems. Ilustration shows the general situation as put forth in a simple sketch by Alain Bernard.
van Bergen and others (2000) made the following remarks:
“The lake chemistry is determined by dissolution of magmatic volatiles, fluid-rock interaction, evaporation of the lake water, dilution by meteoric water and recycling of lake water through seepage into the subsurface hydrothermal system. The lake acts as [a] chemical condenser for volatiles and as a calorimeter trapping heat supplied by a shallow magmatic reservoir. Magmatic volatiles can be supplied to the crater lake system by direct injection of magmatic vapours (SO2, H2S, HCl, and HF) via subaqueous fumaroles or via hot brines entering at the lake bottom.”
van Hinsberg and others (2010) stated the following:
“The crater lake of Kawah Ijen volcano represents the largest body of natural hyperacidic brine in the world (Delmelle and Bernard, 1994) and has been present since at least 1789 (cf. Bosch, 1858). It is characterised by a singularly high dissolved element load (>100 g/L) and very low pH. Fluids from the crater lake seep through [Kawah Ijen’s] western flank to form the acid Banyu Pahit river, the water of which is eventually used for irrigation 40 km downstream [to the North] of the lake in the coastal plain of Asambagus.”
The water in the crater lake has a pH less than 0.3 on a scale of 0 to 14 (7 is neutral). For comparison, lemon juice has a pH of 2; battery acid has a pH of 1. That acidity affects the chemistry of nearby river ecosystems, including the river Banyupahit (Javanese : bitter water).
Originating at the lake, the Banyupahit delivers acidic water to populated areas downstream. According to a 2005 research paper, the river water that local farmers use to irrigate crops has a pH between 2.5 and 3.5. The normal range for stream water, according to the U.S. Geological Survey, is between about 6 and 8.
On August 22, 2013, the Operational Land Imager (OLI) on Landsat 8 captured this view of the lake in East Java, Indonesia. The turquoise color comes from the range of materials dissolved in the water, including hydrochloric and sulfuric acids. The craters of several other volcanoes are also visible within the 20-kilometer-wide (12-mile) Ijen caldera.
The plume drifting west from the crater likely comes from fumaroles, which release hot gases from underground magma. The plume could also come from hot springs and mud pots, according to Erik Klemetti, a volcanologist at Denison University. “The plume is white, so it is likely mostly steam with some other volcanic gases like carbon dioxide and sulfur dioxide mixed in.”
Despite the presence of toxic gases around Kawah Ijen, workers mine sulfur by using a series of pipes installed under one of the volcano’s active vents. Gas inside the pipes condenses into molten sulfur as it moves toward the surface, where it then cools and hardens.
Sulfur Mining at the Crater of Mount Ijen
A strongly active solfatara field (fumaroles that are characteristically sulfurous) is present in the South East part of Kawah Ijen’s crater near the lakeshore, where sulfur-mining activities have existed for many decades. Local workers channel some of the fumarolic gases and molten condensates through pipes and out onto the ground. Once the liquid cools and hardens, workers break the solid sulfur into large pieces and load it into baskets for manual transport out of the crater. According to Wikipedia, miners carry loads of sulfur ore blocks ranging from 75 to 90 kg up a steep trail to the crater rim and then 3 km down the mountain to a weighing station. That and many other web sites show photos of the mining process. Among the more recent photos of the scene are those by Oliver Grunewald (2010) on the ‘boston.com’ web site. He points out that few of the miners possess gas masks.
Two dental studies of miners concluded that they had both higher incidence of dental erosion to the enamel on their teeth (Pranani and Wibisono, 2008) and the gum disease gingivitis (Anitasari and Wibisono, 2008). Both studies attribute these problems to exposure to sulfuric acid fumes. The studies were small (30 miners) and for comparison (control groups) used similar numbers of residents who lived around the mine but did not work as miners.
An active vent at the edge of the lake is a source of elemental sulfur, and supports a mining operation. Escaping volcanic gases are channelled through a network of ceramic pipes, resulting in condensation of molten sulfur. The sulphur, which is deep red in colour when molten, pours slowly from the ends of these pipes and pools on the ground, turning bright yellow as it cools. The miners break the cooled material into large pieces and carry it away in baskets. Miners carry loads ranging from 75 kilograms (165 lb) to 90 kilograms (200 lb), up 300 metres (980 ft) to the crater rim, with a gradient of 45 to 60 degrees and then 3 kilometres (1.86 miles) down the mountain for weighing. Most miners make this journey twice a day. A nearby sugar refinery pays the miners by the weight of sulfur transported; as of September 2010, the typical daily earnings were equivalent to approximately $13 US. The miners often receive insufficient protection while working around the volcano and complain of numerous respiratory afflictions. There are 200 miners, who extract 14 tons per day – about 20 percent of the continuous daily deposit.
A continuous stream of sulfur-laden gases blasts from fumaroles at the lake-side solfatara. These hot gases travel underground in the absence of oxygen. If they are hot enough when they emerge from a vent, the sulfur ignites upon contact with oxygen in the atmosphere. Often the temperature is low enough that the sulfur condenses, falls to the ground as a liquid, flows a short distance, and solidifies. This produces a renewable deposit of mineral sulfur that local people mine and carry to a local sugar refinery that buys it.
Miners walk up the flank of the mountain and then descend dangerous rocky paths down the steep walls of the caldera. Then, using steel bars, they break sulfur from an outcrop, load their baskets, and make the return trip to the refinery. Miners make one or two trips per day carrying up to 200 pounds of sulfur. The refinery pays them based upon the weight of sulfur that they deliver. The rate of pay amounts to a few dollars per trip. Ambitious and physically fit miners can make two trips per day.
Miners have carried hundreds of sections of pipe up the mountain. These have been used to capture the gases produced by numerous vents and route them to a single area where their sulfur spills onto a level work area. This makes collection more efficient and safer for the miners.
Sulfur mining at Kawah Ijen has its hazards. The steep paths are dangerous, the sulfur gases are poisonous, and occasional gas releases or phreatic eruptions have killed many miners.
Ijen and its sulfur mining was featured in the 1991 IMAX film Ring of Fire, and as a topic on the 5th episode of the BBC television documentary Human Planet. In the documentary film War Photographer, journalist James Nachtwey visits Ijen and struggles with noxious fumes while trying to photograph workers. Michael Glawogger film Workingman’s Death is about sulfur workers.
1. Surabaya – Banyuwangi – Paltuding (entrance) – Ijen Crater.
from Paltuding to the crater is about 3 km, can be reach by foot or motor cycle (trail).
2. Gilimanuk (Bali) – (ferry accross Bali strait) – Ketapang Port (Banyuwangi) – Paltuding – Ijen Crater.