Introducing Kawah Ijen Volcano

[BrickFielder]

Introduction
My intention is to produce a series of articles (depending on interest) which introduces ideas about volcanic and earthquake activity. I want to go slightly off the beaten track to explore oddities, volcano hazards, analysis methods, Wonders and Mankind’s impacts. Keep in mind I am not expert (corrections gratefully received), but hopefully these will at least give a flavour of some different places in the world and provide a few minutes escape from people’s troubles.

Introducing Kawah Ijen

Reason for Interest
Kawah Ijen is a volcano made famous by it Blue flames and is obviously a volcano with some unrest, but what piques my interest is the reports from the 1817 eruption. There just seems to be some something about it that is still an puzzling.

The Setting
East Java borders with Central Java to the west, while the narrow Bali Strait to the east separates Java from Bali. Located in eastern Java is also the island of Madura, which is connected to Java by the longest bridge in Indonesia, the Suramadu Bridge. East Java is known for its coastal scenery including Plengkung Beach which reputedly one of the best beaches for surfing.

 

East Java has a tropical monsoon and savanna climate at lower elevation and subtropical at higher elevation. Compared with the western part of Java Island, East Java in general has less rainfall. The average temperature ranges between 19-34 °C.

The Tectonic environment
The Ijen Caldera Complex is located in eastern Java along the volcanic front of the Sunda arc. The mixed  Sunda arc is related to the subduction of the Indo-Australian plate beneath the Eurasian plate along the 1200 km long Java trench. The top of the subducting plate lies 180 km below Kawah Ijen, has an approximate age of 130 Ma at the trench and dips at an angle of 42 Degrees. Convergence of the Australian plate at 7 cm per year is nearly orthogonal near Kawah Ijen.

The Volcano
The Ijen volcano complex is a group of composite volcanoes in the East of Java. The complex is inside an  large caldera Ijen (Kendeng Caldera)  which is about 20 kilometers wide. Many other post caldera cones and craters are located within the caldera or especially along its rim. The Gunung Merapi stratovolcano is the highest point of that complex sitting on the caldera rim.

 

Just to the west of Gunung Merapi within the Caldera is Kawah Ijen with and active crater 722 meters wide and 200 meters deep. Within the crater is a lake which is recognized as the largest highly acidic crater lake in the world. The lake has a turquoise blue colour due to the high concentration of minerals within the water. It is also a source for the river Banyupahit which has a significant detrimental effect on the downstream river ecosystem.

 

There is an active solfatara that emits hot sulfurous gases which ignite as they emerge burning with an electric blue flame. The flames are difficult to see during the day but illuminate the landscape at night. Often the temperature is low enough that the sulfur condenses, falls to the ground as a liquid  and solidifies. This produces a renewable deposit of mineral sulfur that local people mine.

 Kawah Ijen’s has erupted both high-Ca and low-Ca magmas which indicates that Kawah Ijen is tapping both the rim-volcano reservoir and intra caldera reservoir. There is no evidence for physical mixing and mingling implying separate magma pathways for magmas erupted from these different reservoirs.

 
 Kawah Ijen Sulphur Mines
The kawah Ijen Sulphur mines are located down in the crater. Every morning two hundreds miners climb down to the bottom of the crater for the next load of Sulphur. Volcanic gas which escape from fumaroles at the bottom of the crater are directed through the huge ceramic pipes. As the gas cools and condenses in the pipes the gas turns into the liquid Sulphur. This red liquid Sulphur flows out from the pipes to the ground and becomes hard and yellow immediately. The miners then chop lumps of yellow Sulphur off and fill their baskets with Sulphur and then carry the heavy load up out of the crater. Down in the crater the miners dodge clouds of poisonous Sulphur dioxide and hydrogen Sulphide without any mask. Miners carry up to 100 kilograms of Sulphur in baskets connected by yoke 300 meters from the bottom of the crater to the crater rim. He then goes another  kilometer down slope to the weighing station before going another two kilometers through the jungle to the collecting point at Pos Paltuding. Attempts in the past to use mules to do the carrying failed as they were not able to cope with the conditions.

 

Rivers
 The Kawah Ijen crater lake is one of the world’s largest  pools of hyper acidic volcanic water. In 1921 a dam was built on the western crater belt to control the water level in the lake and to regulate the outflow of hyper acidic water in the downstream area,. For several decades the dam’s sluices have not been used as the water level remained below the dam lip. However water from the lake leaks through the rock basement at several points below the dam in to the Banyupahit river. The lake is kept intact by the dam that has been reinforced due to structural weakness but remains vulnerable to even a small volcanic events and earthquakes. 

The river is diluted mainly by two tributaries within the wider Ijen caldera near the village of Blawan and flows down a 50 m high waterfall at the wider caldera rim. After leaving the Ijen caldera, the Banyuputih river flows through the largest single expanse of forest on Java which is part of the Ijen Malang Raung nature reserve. Despite dilution at no point does the Banyupahit river meet water quality standards.  The chemistry of the river water seemed to have changed over the past decade and the negative effect in the irrigation area increased. Any increase in activity would have serious consequences on water quality over a wide area.

Past Eruptions
In 1817 the crater was reported has having fumaroles and a depth of 18m with no lake. The same year the volcano entered an eruptive phase with a 250m deep crater being formed as a result. Eye witness accounts reported ash was dense enough to turn day into night and to make trees and bamboo huts collapse under the weight. At the same time, cold mudflows laden with debris came down the outer flanks of the volcano, following the Banyu Putih valley north and flooding the Asambagus plain, and southeast to Banyuwangi flooding the plains south of it and destroying a complete forest in the process. The impact of the eruption on easternmost Java was severe as large areas of fertile low-lying farmland around Banyuwangi and in the Asambagus plain were covered in sulfur-bearing mud, which hardened into a solid crust, making them unusable for agriculture for several years. By 1820 the lake had formed in the new crater. 

In 1952 there were phreatic eruptions when an ash and Sulphur cloud rose above the crater and 7m gas bubbles were reported in the lake. Variations in temperature have been reported through the years and further smaller gas eruptions were reported in 1957. During April 1993 three gas explosions occurred with a height of 10m accompanied by a strong sulfur smell and a shift in colour of the lake shifted to whitish green. 

There was a swarm of earthquakes occurred to the South West of Kawah Ijen in May 2011. The significant changes in volcanic activity affected the shallow portions of the volcanic system and led the authorities to increase the volcanic alert level to 3.

Recent Activity
In May 2020 a volcanic tremor at Mount Kawah Ijen in East Java triggered the release of poisonous gas and a 3 m high tsunami. The tremor resulted in toxic bubbles of air being released and waves in the crater lake. Local media confirmed that a sulfur miner was found dead a day after.

Discussion
While the blue flames and Sulphur mining catch our attention, what catches my eye is the 1817 eruption impacts downstream. The volume of acidic water that seems to have made its way down stream seems to exceed the size of the lake at that time suggesting to me a reservoir of acidic water beneath the volcano. Human populations down stream do not seem that large, but agriculture would certainly be devastated downstream. Despite water being diluted as it goes downstream it seems to me that very little consideration has been given to the effects on ocean marine environments with the volumes of heavy metals which could be released into the ocean.