Tanah Lot, a Hindu temple whose name means “in the sea,” sits on a sea stack on the southwest coast of Bali, Indonesia. The near-horizontal layered rocks in the sea stack are mostly lahars (violent water-driven mud and debris flows descending from the flanks of volcanoes) and volcanic ash falls probably from Batur, one of the two active volcanoes on Bali (the other, more famous one is Agung). Some of the layers may be from the older more-or-less extinct Buyan-Bratan volcanic complex. Either way, those debris flows traveled 50 kilometers or more from the volcanic vents to this location.
Batur has been active fairly continuously since before the 1840s (the oldest documented eruption is from 1804), but its eruptive history is much older than that. A large caldera-forming eruption is dated to about 24,000 to 28,000 years ago, and that, combined with even older eruptions, probably created the wide plain of south-central Bali that includes this section of coast.
The word lahar is straight out of Javanese for those volcanic mud flows. It’s been part of western geologic jargon since 1922.
Two islands east from Bali is Sumbawa, site of Tambora volcano that erupted in 1815 and whose dust, ash, and aerosols created the Year without a Summer in 1816, causing extensive crop failures, famines, and bleak enough weather that it drove Mary Shelly to write the novel Frankenstein.
Ijen is the easternmost volcano in Java, just across the Bali Strait (2.4 kilometers wide, 1.5 mi, at its narrowest) from Bali. My friend Phyllis Hargrave acquired this native sulfur (photo above) there in 2004. The specimen is about 12 cm high.
Molten sulfur in the volcano’s crater is on fire, burning with a blue flame and making for quite a tourist attraction, and the crater lake is among the most acidic in the world, with a pH (acidity) of 0.1 to 0.5. Compare the worst levels of Butte’s Berkeley Pit at about 2.1, and now the Berkeley Pit is around 4.5; a pH of 0.5 is 5000 times more acidic than a pH of 4 on this logarithmic scale where 7.0 is neutral. A couple hundred miners risk their lives to harvest the sulfur for industrial uses as well as specimens for tourists. The molten or vapor-phase sulfur is channelized through ceramic pipes and poured into molds to solidify for transport from the volcano. I guess you could fairly call this piece a dripstone, a version of a stalagmite-like formation.
Some would say this is not a mineral, because it formed at least partly through the intervention of humans. The usual definition of a mineral is something like “A naturally occurring inorganic element or compound having an orderly internal structure and characteristic chemical composition, crystal form, and physical properties.” The sources of argument there are “naturally occurring” versus man-made, and “inorganic,” which some might say excludes things like the calcite or aragonite in a mollusk shell because the animal made the calcite, which is otherwise identical to any other calcite, or it might exclude minerals based on “organic” (carbon-based) ions such as the oxalates (C2O4), even though they occur in places as diverse as hydrothermal veins, ocean-floor sediments, and coal seams.
To me such distinctions are largely semantic and conventional, and based on arbitrary definitions. Granted that the IMA (International Mineralogical Association) has the official say on such matters, I don’t have to agree with all of that, and I don’t. I think how a mineral was made is largely irrelevant (but might be noted and could be quite interesting), whether by non-organic physical processes, natural biogenic processes, or even by intentional effort by humans.
In any case, sulfur is rarely mined directly like this material from Indonesia. In the US, about 93% of all sulfur produced is a byproduct of petroleum and natural gas processing, with the remainder as a byproduct of sulfide mineral processing. Butte is credited with nearly 10 million tons of historic commercial sulfuric acid production, and there’s a lot more in the Berkeley Pit water that we could do without. The U.S. produces about 8 million metric tons of sulfur a year, worth about $740 million.
The vast majority of sulfur, more than 90%, is used to produce sulfuric acid, the most voluminous chemical made in the world. In turn, the overwhelming majority of sulfuric acid is used to digest phosphate rock to extract the phosphorous to make fertilizers. The remaining sulfuric acid is mostly used as a feedstock for a wide diversity of other chemicals, and finds its way into dyes, pigments, detergents, paper, medicines, explosives, water treatment, insecticides, gunpowder, matches, and rubber.
The photo by Candra Firmansyah (2015, shared under the Creative Commons Attribution-Share Alike 4.0 International license, via Wikipedia) shows “traditional sulfur mining at Ijen Volcano, East Java, Indonesia. This image shows the dangerous and rugged conditions the miners face, including toxic smoke and high drops, as well as their lack of protective equipment. The pipes over which they are standing serve to guide sulfur vapors and condense them, thereby easing (well, relatively at least) production. What looks like clouds or steam is actually highly concentrated hydrogen sulfide and sulfur dioxide gases.” (Quoted from Wikipedia)
The sulfur-rich Ijen volcano, along with all the other volcanoes in Java, are the result of subduction of the Australia-India tectonic plate beneath the Sundaland extension of Eurasia. The part of the Eurasian Plate that is in Southeast Asia, Sumatra, and Borneo is sometimes called the Sunda Plate, and it is being pushed to the southeast, over the northward-moving Australian Plate, because of forces related to the collision between India and Eurasia several thousand kilometers to the northwest. Southeast Asia and Borneo are essentially being “squeezed” out from the corner of Eurasia where India is pushing in. When continents collide, something (often a lot of somethings) has to give.
At Java, the Australia-India plate is oceanic and Sundaland is continental, so this is a fairly standard subduction zone, albeit a very active one in terms of both volcanism and seismicity. Toba in North Sumatra erupted about 74,000 years ago with a volume greater than the largest Yellowstone supervolcanic eruption 2.1 million years ago and may have been a factor in a postulated genetic bottleneck in human and other primate evolution. Krakatau, between Java and Sumatra, exploded in 1883 with the loudest known sound in recorded human history until (perhaps) the eruption in Tonga in January 2022. The 2004 M 9.2 earthquake and ensuing tsunami that killed almost 230,000 people was on this same subduction zone.
A nice study of the Ijen volcano and its setting is in Caudron and others, 2015, Kawah Ijen volcanic activity: a review: Bull. Volcanology 77:16.
World sulfur production totals about 80 million metric tons a year. China is the leader with about 21% of the total, and the U.S. is second at about 10%, but the US is still a net importer of sulfur, mostly from Canada and Russia, with imports at about 18% of US consumption in 2021. Russia, Saudi Arabia, and the United Arab Emirates are also leading sulfur producers (around 7% to 9% of the total each) because they are also major oil and natural gas producers.
That was fun
Wow, great read!