The author at a Yunotani hot spring. This spring supplied hot water for the Yunotani spa (now closed). Photo by S. Yoshikawa.
Yunotani is a hydrothermal area inside the Aso caldera, not too far from the Aso Volcanological Laboratory (AVL), located in central Kyushu, Japan. Maybe thirty or forty years ago there was a hotel here that was used by visitors to the nearby hot springs. Now the hotel is closed, and the experimental geothermal power plant, originally built by NEDO (the Japanese agency for the Development of New Energy and Industrial Technology) stands nearby, decaying and unused. I don’t know why the hotel closed, but with so many spas in close proximity it’s easy to imagine that demand just wasn’t high enough to keep one more resort going.
This hydrothermal power plant provided power for the defunct hotel. Now it rusts slowly away, unused.
At one time Yunotani was an active volcanic area. Not just a geothermal area, but the site of phreatic vulcanism. Phreatic vulcanism happens when hot, rising magma encounters shallow groundwater. The groundwater flashes to steam, and the sudden volume expansion is a kind of explosion that can leave behind a large crater. Ubehebe crater in Death Valley, California, is an example of this type of volcanic eruption.
The phreatic eruption at Yunotani happened in 1881, which is long enough ago that the trees and bushes have grown over the original scars, and I have a hard time finding evidence of the crater. Walking up the hillside above the hot springs and the original hotel, I find instead a grassy meadow and the ruins of some tumbledown shelters. I’m told this was a popular area for camping some years ago–thus the remains of the wooden buildings. There used to be great trees in this meadow, but they were cut down to make more space for camping. The stumps still remain, though, and I’m interested to see that each tree grew over a steam vent. Steam still rises from between the roots of the old stumps; when the trees were living, the steam provided a constant source of moisture that nourished the grove.
This tree, and many like it, grew over steam vents to take advantage of the year-around supply of water.
On closer inspection I can see that the steam still fosters life in this meadow. Not just the grass that grows so luxuriantly but, nestled in the roots of the old stumps, I can see growths of moss thriving on the condensate from the steam. What a perfect environmental niche for a plant that loves moisture and low light!
Moss, clustering in the tree roots.
I suppose many people think of geothermal areas as harsh and devoid of life, but in fact the opposite is true. Hot springs and hydrothermal areas in general provide a rich niche for life, in spite of the apparently uninviting conditions that often prevail. Ever since Thomas Brock’s remarkable discovery in 1966 of thermophilic (heat-loving) organisms growing in a Yellowstone hot spring, it has been recognized that life abounds pretty much everywhere on Earth–and perhaps beyond. Even Yudamari, the hot, hyper-acidic lake in the crater of Nakadake volcano (see “A Visit to Nakadake Crater” in this blog) is likely teeming with life, although to the best of my knowledge nobody has looked for it yet in that inhospitable place. Thermus aquaticus (as the organism discovered by Brock came to be known) and other extremophilic organisms live in an astounding array of environments: hyper-saline, hyper-alkaline, hyper-acidic, and hyper-baric (high pressure), not to mention at temperatures to just over 120 degrees celsius (248 degrees Fahrenheit, the current record for the hottest temperature a viable organism has been found to tolerate). In fact, it has been said that perhaps the largest reservoir of biodiversity on our planet is not the rain forests, as many might think, but the genetic pool contained within the bacteria and archaea of the world’s hot springs.
What do these extremophiles eat? It turns out that all life gets energy from “oxidation.” I put the word “oxidation” in quotes, because the process doesn’t necessarily involve oxygen. Instead, oxidation is the process of pulling electrons off of one atom and dumping them on another; the excess energy generated from this exchange is the engine that powers all life, from the most primitive archaea to prokaryotic organisms such as amoebas and humans (amoebas and humans differing but little in this classification scheme).
Micro-platelets of iron pyrite, floating on the surface of a Yoshioka hot spring.
Water from this free-flowing geothermal well in the Alvord Basin of Oregon, USA, nourishes vibrantly colored microbial life. This photograph, taken by College of Science Assistant Dean Tom Williams, was the cover image of the October 2004 issue of Geology.
