Averting an Acid Apocalypse: The Toxic Legacy of Kawah Ijen

Sulfur deposits at Ijen Crater — Molten elemental sulfur (orange) and solid sulfur deposits (yellow) at Ijen Crater.

(Image credit: Jeffrey Johnson)

Jeffrey Johnson, associate professor of geosciences at Boise State University, contributed this article to Live Science's Expert Voices: Op-Ed & Insights.

There are approximately 250 million vehicles in the United States. Imagine the lake of acid that would form if each car, truck and motorcycle leaked its battery's contents into one large pit. The resultant reservoir would measure more than a million cubic yards and fill a space equivalent to one of the world's largest sports stadiums. Such a gargantuan pool would contain acid caustic enough to burn skin and dissolve metal. It would represent an environmental menace and an ecological disaster.

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Though both car batteries and Kawah Ijen's lake are primarily composed of the same sulfuric acid, Kawah Ijen's sulfur is tapped naturally from its volcanic host. This sulfur is sourced from a magma reservoir somewhere beneath the 650-foot-deep, opaque aquamarine waters. The magma is continuously "exsolving," or venting, a brew of carbon dioxide, sulfur gases and other volatiles. The sulfur gases are mostly "scrubbed" by the circulating water of the hydrothermal system, which is linked to the lake above. There, bubbles of sulfur gas combine with hydrogen ions to produce sulfuric acid. [Stranger than Fiction: Volcanic Eruption Creates Deadly Acid Lake ]

Workers navigate through gas clouds and around superheated fumaroles. The 600-degree Fahrenheit (~300 degrees Celsius) vents are hot enough to melt the yellow rock, and it flows over short distances as an exotic golden-hued "lava." The gas concentrations are potent enough that they react with one another, precipitating elemental sulfur, which is a neon-yellow solid. The sulfur is mined by locals, who risk the poisonous gases to collect large blocks — carried out in impossibly heavy wicker baskets. In the past, the mineral was used as a constituent in gun powder, but now it is primarily used to bleach sugar.

"Kawah Ijen volcanic activity: a review," is a study led by Corentin Caudron of the University of Cambridge and published in 2015 in Bulletin of Volcanology. It chronicles the dynamic history of the crater lake volcano, including its most significant historic event in 1817. That "phreatomagmatic" eruption was particularly violent owing to the interaction between magma and both hydrothermal and lake waters. It is a reminder that magma resides close to the surface and that future potent eruptions are likely.

The 1817 paroxysm, which began Jan. 16, featured explosions and incandescent eruption columns that endured into February. The Caudron paper summarizes 19th-century eyewitness accounts of widespread devastation around the volcano , of watersheds destroyed by acid effluence as far as the ocean, of ashfall dense enough to turn day to night, and of bamboo huts collapsed under the weight of tephra (fragments of rock). Reports also reveal the notable disappearance of the acid lake and a deep crater in its place.

At the time of the 1817 paroxysm, there were no population centers near the crater lake, but this is no longer the case: Java is the most populous major island on Earth, and its 141 million people constitute a density about 10 times that of California. Should a comparable eruption occur today, acidic volcanic mudflows (or lahars) would overspill the lake's western levee and enter into the Banyu Putih valley and associated irrigation systems. It would also put tens of thousands of people at risk.

For example, energetic lake surface activity in 1917 — 100 years after the magmatic eruption — was possibly triggered by a local, non-volcanic earthquake. Corentin's references speculate that earthquake shaking could have "sloshed" some water up and over the western dam, which would have led to a lowering of the lake level and potential volcanic activity. Diminished lake depth would have led to lower pressures at the lake bottom, upsetting the volcano's delicate hydrothermal system. That is, lower pressure would have encouraged greater boiling and degassing.

This mechanism suggests a probable, and potentially hair-trigger, feedback risk. Vigorous bubbling of the lake might spill significant lake water. Alternatively, a regional earthquake or spontaneous landslide from the crater's steep walls might cause a seiche of water to overspill into the lake's outlet. Either one of these "tidal waves" would lead to a drop in confining pressure, as if the lid was removed from an enormous pressure cooker.

Indonesian nationals monitored Ijen more comprehensively following the country’s independence in 1945. Authorities who noted intermittent periods of explosive degassing from Ijen installed seismometers, the backbone of volcano monitoring, in the 1980s. More explosions reported by miners and tourists in the 1990s and elevated earthquake activity in the early 2000s prompted occasional closures of the crater.

Ijen is classified as a type example "wet volcano" and the researchers convened a special "Wet Volcanoes Field Workshop" in the fall of 2014 to test and implement an array of suitable monitoring techniques for this relatively special type of volcanic system. The outcome was a Geological Society of London Special Publication highlighting strategies for improved monitoring of Ijen. The paper, led by Hendra Gunawan from Indonesia's Centre for Volcanology and Geological Hazard Mitigation, demonstrates the capabilities and challenges of traditional monitoring techniques applied to Ijen.

Seismic, or earthquake monitoring, is most commonly employed at volcanoes worldwide, and is used to track an uptick in earthquake activity, which generally precedes eruptions. Seismic monitoring at Ijen is complicated, however, because of the high level of continuous background shaking. Ijen's active hydrothermal system includes boiling of ground water, which contribute to a constant vibration, or tremor. Against this noisy backdrop, a solitary seismometer might not be capable of detecting critical earthquakes initiated by the motion of magma. As a result, researchers in this study deployed an array of seismic instrumentation, with many seismometers clustered closely together. That array serves as a sensitive stethoscope, differentiating background noise from potentially more ominous earthquakes.

Deformation monitoring, in which the shape of the volcano changes subtly, is complementary to seismic techniques and it indicates potential migration of magma over longer time scales. The Ijen deformation studies included precision mapping of more than 1,400 high-resolution photos taken with SLR cameras from a variety of vantage points around the crater. This powerful, and relatively new, mapping technique is called "structure from motion" and produces submeter scale digital elevation models for Kawah Ijen. Repeat surveys in future field campaigns will now be able to map and explain areas of critical ground deformation and landslide occurrence.

For gas remote sensing, the research team integrated several technologies: Multi-gas sensors sampled fumaroles and lake water directly, whereas ultraviolet cameras and spectrometers remotely measured sulfur emissions from crater and lake edges. Some of the techniques are new, such as diode laser spectroscopy, which revealed elevated carbon dioxide emissions from the lake's surface as these gases percolate upward from lake-bottom vents. Future changes in the ratio of carbon dioxide and sulfur emissions — and their amounts — are critical indicators of possible unrest at many volcanoes, including Ijen.

Finally, the team employed thermal monitoring at both lake and fumarole fields to map surface temperatures and to directly measure fumarole temperatures (up to 650 F, or 340 C) and lake temperatures (around 90 F, or 30 C). In the past, increasing lake temperature (reaching more than 120 F, or 50 C) has been an indicator of enhanced heat advection and a potentially troubling indicator of pending magmatic activity.

History indicates that threats from this type of wet volcanic system are very real. Ruapehu, a far smaller acid lake in New Zealand, is testament to what could happen. In 1953, that crater lake's natural sediment dam, weakened by acid alteration, failed catastrophically, and in the absence of a landslide, earthquake or magmatic eruption. A relatively small lahar was generated, destroying a rail bridge 2 hours downstream. Shortly afterward, a passenger train crashed from the ruined track, killing 151 of 285 people onboard. This tragedy, known as the Tangiwai disaster, was due to a Ruapehu flood that is some 100 times smaller than the volume of acid waters currently impounded at Kawah Ijen.

A virtual certainty is that one day Ijen's waters will catastrophically release, either during explosive volcanism or destabilization from regional earthquakes or landslides. Improved monitoring efforts will not avert such an event, but will be vital for anticipating when and how big the event might be — necessary to plan for hazard mitigation. In this manner, volcano scientists working with health and safety authorities strive to minimize impact for at-risk communities.