The author, with Nakadake crater in the background. Photo by S. Yoshikawa.
Last Friday I was in my office at the Aso Volcanological Laboratory (AVL), working away on some equations (because I’m a hydrogeologist, I spend a lot of time working with equations and computer models!) when there was a knock on my door. I turned around to find my friend Yoshikawa-san standing there. “I must go to Nakadake crater to fix a seismometer. Also, I will take temperatures at the crater. Do you want to go?” Did I?! You bet!
Of the five main volcanos inside the Aso caldera, Nakadake is the only one that is currently active. There were eruptions in 1998 and 2004, and there is constant hydrothermal activity at the summit. Inside the summit crater is Yudamare (”Hot Water Lake”), an acid, fuming body of water that is surrounded by an atmosphere so poisonous that it can’t be approached very closely. Of course, being a hydrogeologist that studies geothermal systems, I’ve been wanting to visit this hydrothermal Mecca. Here was my chance!
Nakadake is one of the few volcanos in the world where visitors can go right up to a viewing area close to the rim to look down into the active crater. As we drove up the road there were dozens of people walking up, walking back, or taking cars, buses, or the alpine tram to the summit. What a zoo, I thought. Still, most people can only go as far as the observation platform, I reasoned–as soon as we get out of the parking lot we’ll be on the rim and away from the crowd. I had no idea how right I was! It didn’t take long before we had left the bus loads of school children and tourists behind, and then… my first view into the crater!
Standing on the rim of Nakadake crater (photo by S. Yoshikawa).
I can’t even describe to you how it felt to stand on the edge of that unworldly landscape. There were no sounds but the rush of wind and, far below, the hiss of steam jetting out of the fumaroles in the crater wall. Yudamare lake looked like a weirdly green, steaming caldron, roiling and bubbling, and the upper part of the crater looked like a vision from Dante’s Inferno (no exaggeration!). I asked Yoshikawa-san, a little hesitantly, about going down inside the crater. “Well, with our gas masks we could go down as far as that valley over there” he gestured thoughtfully to the area above the fumaroles, “but if we go below that, I think we will die.” Okay, scratch that idea…
About this time I heard, indistinctly, a loudspeaker announcement over at the summit lookout, and noticed all the tourists in the parking lot were leaving. “What’s going on?” I asked. “Oh, they are closing the summit area because of the gas.” Sulfur dioxide and hydrogen sulfide come up out of the fumaroles. In low concentrations these gases cause the rotten-egg smell many people associate with hot springs, but in high concentrations they combine with the moisture in your lungs and turn to sulfuric acid. I knew several tourists were killed that way a few years ago. “Well, okay” I said. I started packing up our stuff, but Yoshikawa-san stopped me with a smile. “It does not apply to us” was all he said. I was thinking privately that I wasn’t sure whether it should apply to us or not: my nostrils were stinging and my skin was itching from the tiny droplets of acid that floated in the air. “We’re lucky,” Yoshikawa-san said, looking up at the sky. “There is good wind today, so it’s not so bad here.” Indeed…
Setting up to take temperature readings from the crater rim.
Yoshikawa-san takes the crater's temperature.
In my research I work a lot with hot spring temperatures, and generally we collect them by the hundreds or thousands, using digital thermometers and various kinds of thermocouple probes. Without being able to access the crater directly, though, the AVL scientists use a different method: an infrared camera. After a brief set-up, Yoshikawa-san started taking temperature data. The lake, it turns out, was only 60-65 degrees celsius (140-150 degrees Fahrenheit), which would still cook an egg, but at least it wasn’t boiling. The extreme acidity of the water, however, was another matter, since the lake boasts a pH of 1 or less (it has been known to go into negative numbers). Then Yoshikawa-san turned the camera on the area of fumaroles in the crater wall.
Fumaroles in the Nakadake crater wall. The yellow stains are native sulfur deposits left by the steam.
Close-up of the Nakadake fumaroles.
“Can you read the temperatures?” he asked. I grabbed greedily at the camera, but stuttered a little as I read out the values I saw there. Was this thing working right? I shook my head. “Uh, it looks like the maximum temperature I see is… about 530 degrees celsius…” That’s 986 degrees Fahrenheit! Yoshikawa-san showed no surprise. “Yes, at night you can see the vents glowing in the dark.” Whoa….
Finally we gave up on temperature monitoring and fixed the faulty seismometer. My role in that was pretty minor: “Jerry-san. Please jump up and down” Yoshikawa-san asked very politely. “Ah, still not working. Please jump again.” Eventually he got it working and we began the trek back to the observation platform. On the way, I had a thought. “Yoshikawa-san,” I began, “you said you have to go next month to change the temperature sensors that have gone bad?” “Yes” was all he said, not looking at me. “You have to go inside the crater to change the sensors, don’t you? Down into that valley?” “Yes.” Still no expression. “You… you wouldn’t go without me, would you?” He looked at me and smiled. “No, Jerry-san. I would not go without you!” We both laughed.
I can’t wait…!
Photo and matching thermal scan of the fumarole area of Nakadake crater. The temperatures shown are in degrees celsius.
Tags: Aso caldera, geothermal, Japan, Jerry Fairley, Kyushu, Nakadake crater
Jerry - Really enjoyed all the sites and pictures. I saved some of the pictures (with you in them) and printed them all out for Dad. Have forwarded the addresses to several people.
Love you - Mom
Well, at least my Mom liked the postings. Thanks Mom!
The pictures and description of your adventures are out of this world.
It’s amazing how much you have done during your first month in Japan. Your explanations of your experiences and the historical geologic activity behind the area are excellent. I look forward to seeing your presentation on the research that you have been doing in Japan. You should have Debbie send out an email for you about your blog so that your students can stay updated. Stay Safe on your adventures.
Hi Attila–thanks for the kind words about my blog entries! I’m glad you find them entertaining and informative; I’ve certainly learned a lot in the little while I’ve been here! I should say that most of my experiences here have been thanks to the kindness and hospitality of my Japanese hosts at the AVL.
In any case, I will try to stay safe, and I look forward to presenting my research when I return to the States. In the meanwhile, I hope you’ll keep reading! Please say “hi” to everyone for me. J.