Japanese school girls wearing hard-hats

Live tube worms in Kagoshima city aquarium

Fumarole depositing sulphur

However, my main destination was not Kagoshima city but the little island of Iwojima, four hours by ship to the south. Iwojima means "sulfur island" in japanese and Japan has several Iwojimas. This one is sometimes known as Satsuma-Iwojima, after the samurai-era name for the Kagoshima region, to distinguish it from the others (such as the infamous Iwojima of WWII, which lies south of Tokyo). The day I was supposed to leave Kagoshima, the boat was cancelled because of stormy weather and 13-foot waves, but no time was wasted because a kind local collector took me to the type locality of osumilite, on the Osumi peninsula near Kagoshima, and I was able to find several nice crystals in spite of the cold wind and rain. The next day, waves had diminished to 8 feet, still windy, with intermittent rain, and we shipped out. (Barf buckets provided for the weak of stomach.) About half the passengers were local islanders going home, and half were government employees travelling for such purposes as school maintenance, water supply inspection, to fix the post office's computer... I was the only foreigner on board.

Debris dam below Iwodake; acid steam rising in distance

Fumarole depositing sulphur

   The first thing one notices as the ship approaches this little 4.5 square mile island, population 135 and declining, is a smell of sulfur in the wind. Then the frighteningly steep and jagged slopes of the 2,300-foot high Iwodake ("sulfur peak") volcano loom up out of the grey drizzle, dropping straight down into the ocean, with no beach. Rounding the volcano, the landscape to the west gets relatively more gentle and a little bay with a harbor appears, the harbor filled with red-brown water the color of old blood, slowly oozing out into the transparent blue waters of the surrounding sea. Our ship steams into the harbor entrance, churning up the red and blue water boundary like a giant paint mixer. (More on this red water later.) As I was getting off the ship, three people asked me whether I had come to study African drumming and dancing! Or was I the new drumming and dance teacher perhaps? Turns out Asia's only school for such African arts is in this unlikely setting, and this seems to be the island's second main industry, after catering to rich sports fishermen. (To round out the economy, islanders also export a few beef cattle, cooked bamboo shoots, and camellia flowers for cosmetic products.)

Ferry leaving Iwojima port.

Ferry entering Iwojima port

After dropping off my luggage at a B&B, I went hiking to scout out trails to potential collecting sites. During the next hour I ran into large wild peacocks several times. A now defunct resort hotel had brought a few which have bred themselves wild over the island. In fact, peacocks have become a pest, and are one of the reasons, along with water scarcity and sulfurous acid vapors, that Iwojima has few vegetable gardens compared to other southern islands. Ah well, if one must have pests, they may as well be beautiful.....But I had better start talking about geology and minerals, before anyone forwards this manuscript to Travel & Leisure.

Peacock wandering the Village

   Iwojima constitutes a small segment, about 2.5 miles long, of the northwest rim of Kikai caldera, a giant explosion crater which is mostly under the ocean now. Kikai blew up 6,300 years ago, around the time human civilization was just getting started (the world's first stone temples were going up in Malta; the pyramids of Egypt weren't even on the drawing boards yet), and the shattered debris of Kikai's suicide spread north and east in thick clouds that left ash beds over much of Japan and Korea. We can assume that large numbers of the Jomon people who then inhabited Japan and Korea came to an abrupt and choking demise. A vertical cliff curving across the middle of Iwojima is all that is left of the original caldera wall. Iwodake, the smoking volcano that dominates Iwojima's landscape lies inside the caldera wall, and so must be younger than 6,300 years old (actually much younger).

   Iwodake is an ecologically instructive volcano. There are fumaroles and solfataras inside the crater and on the outer slopes, pumping out into the atmosphere several hundred tons a day of acrid SO2 gas (future acid rain!), and smaller quantities of even nastier gases like HCl, H2S and HF, plus 1 to 10 tons per year of each of a long list of metal vapors, including Fe, Sn, Mo, Zn, and poisonous heavy metals like Pb, Hg and Tl too. This is an eye-opener for those blissful souls who believe Nature is benign and only human activities pollute. (What are the EPA and OSHA doing about this? Perhaps a great big cork might help?)

Remnant of Kikai caldera wall cutting across the Iwojima landscape.

Remnants of Kikai caldera wall.

   Some of the fumaroles inside the crater are unusually hot - 600 to 900 degrees C - and have been putting out high-temperature heavy-metal-laden acid gases for at least 800 years. The rocks around active vents are red hot. Microcrystals of molybdenum, lead and thallium minerals are also being deposited - very educational for economic geologists, who more and more are recognizing that some valuable metal deposits were transported and concentrated by Nature in the gas phase rather than by liquid water (hydrothermal processes). Published reports on the minerals of these high-temperature fumaroles are what had first gotten me interested in this island: molybdenite, wulfenite (first recorded locality in the world for wulfenite as a fumarolic mineral), anglesite, ilsemannite, challacolloite, and two new but still undescribed thallium sulfides (Tl-Pb-sulfide and Tl-Bi-sulfide).

Higashi hot springs at low tide.

Higashi hotsprings at high tide.

   The crater of Iwodake was the remarkable venue for two periods of mining. The first activity, for sulfur, began around 1542 when the Portuguese introduced firearms to Kagoshima and Lord Shimazu needed sulfur for making gunpowder. Sulfur mining for more modern industrial purposes reached a peak in the 1950s, with production ranging from a couple hundred to several thousand tons per month. Old photographs show workers carrying pickaxes, hiking single file up the trail to the crater. Fumarolic sulfur was dug both inside the crater and on the southern external flanks of Iwodake, and was sent to the coast by a cable that ran down the south slope of the mountain.

Distant view of Iwodake volcano with fumaroles.

An unusual form of native sulfur here are the sulfur "trees" that grow over some low-temperature fumaroles - twisted branching chimneys that grow to over a meter high before the hollow sulfur pipes break off and the process repeats itself. I found native sulfur also as elliptical alluvial pebbles on sand in some of the gullies draining Iwodake. Their low density ensures they "float" on top of sand banks, rather than sinking to the bottom like gold nuggets.

A second phase of mining started in the 1970s, this time not for sulfur but for silica in the form of keiseki, the japanese name for an unusual "chemically metamorphosed" rock type composed almost entirely of cristobalite, tridymite and opal (97% SiO2), as snow-white masses formed when very acid fumaroles leached all the Al, Fe, K, Na, Ca, Mg, etc. out of the rhyolite around the summit of Iwodake.

Eruption shelter, Sakurajima volcano.

A modern mining company took over the high peaks, built a paved road up to the crater rim, hired local men to drive bulldozers, and erected a 2.5 kilometer cable to carry silica rock down the southwestern slopes to the port; no more impoverished miners with pickaxes climbing up steep footpaths. Production peaked at well over 40,000 tons per year. The keiseki was used for ceramics, for making "water glass" (sodium silicate gel), and for "white carbon" (whatever that is).

   Mining finally came to an end in 1996, not because of lack of keiseki, but because of the availability of cheaper imported silica and because the emissions of acid gases reached unbearable levels. A local man who used to operate a bulldozer in the crater told me that the fumarole gases increased so much that his skin would itch, clothes and shoes would turn brittle and fall apart in a week, tooth enamel got rough and pitted in a few days, and something would happen to ones hair and beard (my japanese language skills weren't good enough to understand exactly what happens to hair and beards, but it sounded horrible). The mining company's 2-floor office building is now the African drum and dance school.

   One might ask what happens to all the many thousands of tons of K, Al, Fe, etc., leached out of the rhyolite; where does it go? The answer is: Hot springs. There are at least six on Iwojima, five among the rocks of its jagged coast, and one under the seawater in the port. Higashi hotsprings emits crystal-clear water and has been dammed up with some strategically placed stones and cement, forming pools of different temperatures where one can elect to either boil oneself alive or have a nice relaxing hot soak under the stars, depending on which pool one steps into. But learn from my painful experience and do not rub your eyes after wetting your fingers in the pool; the water is rich in highly astringent potassium alum and other acid aluminium sulfates (and a trace of arsenic). (So that's where all the K and Al in the leached-out feldspars went; I had been wondering... and one must sometimes suffer pain for science.) This astringent water is alleged to be good for the skin, getting rid of wrinkles and making you look younger.

Standard Iwojima picnic lunch wrapped in leaves

Akayu hotsprings nearby (Akayu means "hot red water") and Nagahama hotsprings under the port emit very iron-rich water, with lesser amounts of manganese. The water in the port contains 191 ppm ferrous iron - an extraordinarily high concentration for seawater!

Microbes metabolize the soluble ferrous salts, producing ferric hydroxides (which is what gives the seawater its red color) and precipitating what the microbiologists call "biomats", which consist of the mineral species goethite, ferrihydrite, buserite and birnessite, precipitated around microbial filaments. The biomats cement sand grains together, forming "bioterraces" which under ideal conditions can grow remarkably rapidly - up to one meter thick in three months! (Looking back at Precambrian banded iron ores, one wonders whether perhaps these accumulated much faster than we thought.)

   Well, I regret to say I never made it close enough to the high-temperature fumaroles to get any wulfenite or thallium sulfides; too worried about damaging my lungs and camera, or perhaps just choking to death. Anyone less chicken than me who is planning to try this should take a respirator with full face mask, like the old gas masks from WW 1, and asbestos-soled boots. The abundant keiseki doesn't have any vugs with crystals, but I did find a few pieces with tabular yellow inclusions of native sulfur pseudomorphs after feldspar crystals, and many impure keiseki boulders encrusted with bright red botryoidal hyalite opal, presumably colored by ferric iron oxide (hematite) probably formed by hydrolysis of ferric chloride-rich fumarole gas.

The prize finds of my field collecting on Iwojima was a lump of highly altered vuggy rhyolite, rich with beautiful microcrystals of transparent blue roedderite (much nicer color, if I may say so without offending the Germans, than the roedderite from the Eifel hills). Also one boulder with dark green acicular hypersthene and some excellent tridymite trillings up to 6mm - relatively large for tridymite.

Shrine gate, looking towards Iwodake.

References:

Africano, F., et al. (2002) Earth Planets Space, 54, 275-286.
Hamasaki, S. (2002) Earth Planets Space, 54, 217-229.
Kazue, T. (2000) Clays and Clay Minerals, 48, 511-520.