A Wetland Landscape Created by Volcanic Activity
The area around Chatsubomi-goke Park forms part of a larger wetland system created by the volcanic activity of Mount Kusatsu-Shirane. Impermeable volcanic soils, depressions, and crater-like landforms allow water to collect, producing a series of marshes, ponds, streams, and other wetland environments.
Nearby are Yoshigadaira Marsh, Ōdaira Marsh, and the crater lake of Yugama. Together, these landscapes form a distinctive highland environment in which water and volcanic geology interact.
Yoshigadaira Marsh lies at approximately 1,832 meters, while Ōdaira Marsh is located at around 1,600 meters. Acidic water, geothermal heat, and warm groundwater all contribute to the development of plant communities rarely found elsewhere.
Anajigoku — A Strongly Acidic Spring Environment
The central feature of Chatsubomi-goke Park is a bowl-shaped depression known as Anajigoku, literally meaning “Hell Hole.” Formed by volcanic activity, it lies near the headwaters of the Motoyama River.
Mineral-rich water emerges from the ground at approximately 20°C and has a strongly acidic pH of around 2.6–2.9. The water contains substantial amounts of iron and sulfate ions, creating an environment that is highly unusual for plant life.
A Brilliant Green Carpet of Moss
Yet this seemingly harsh environment is precisely what allows Chatsubomi-goke to thrive.
The moss spreads across the mineral-rich landscape in vivid shades of green, sometimes appearing like a brilliant natural carpet. Its ability to survive in strongly acidic water is one of the most fascinating aspects of the site.
Chatsubomi-goke is particularly rare in mainland Honshu, and the colony here is regarded as one of the largest of its kind in East Asia. The unusual combination of acidic water, volcanic geology, and biological adaptation makes the site valuable not only for sightseeing but also for scientific research.
National and International Recognition
The importance of Chatsubomi-goke Park extends beyond its visual appeal. On May 28, 2015, the Yoshigadaira Wetlands, including the Chatsubomi-goke habitat, were registered under the Ramsar Convention, an international framework for conserving wetlands of global importance.
On February 9, 2017, the site was designated as a National Natural Monument under the name “Iron Ore Formation Site of the Kuni Chatsubomi-goke Biological Community.”
This designation recognizes not only the moss community but also the geological processes involved in the formation of iron ore. The site therefore represents a rare combination of biological and geological heritage.
Walking Among the Moss
Walking paths have been established around the park, allowing visitors to observe the moss colony without entering sensitive areas. From the designated viewing areas, the vivid green landscape and unusual mineral environment can be appreciated safely.
In recent years, Chatsubomi-goke Park has also been introduced as a spiritual or “power spot,” attracting visitors interested in the distinctive atmosphere of the site as well as its natural and historical significance.
The History of the Gunma Iron Mine
Long before the area became a nature park, it was an important mining site known as the Gunma Iron Mine or Kusatsu Mine. The mine produced iron-bearing minerals, including limonite and iron alunite.
The formation of the iron deposits is closely connected to the unusual chemistry of the site. Iron dissolved in strongly acidic spring water can be taken up and transformed through biological and chemical processes involving organisms such as mosses and iron-oxidizing bacteria. Over long periods, iron-rich deposits accumulated in the surrounding environment.
Dating of deposits on the cliffs suggests that iron formation in the area has continued for more than 10,000 years, long before modern mining began.
A Mine Developed During World War II
Full-scale mining began in 1943, during World War II, when Japan faced shortages of important metal resources.
Nippon Kokan Mining developed the mine and established transportation infrastructure to move the ore. A dedicated railway was constructed toward Taishi Station on what was then known as the Naganohara Line, later incorporated into the Agatsuma Line. A cableway was also used to transport materials across the mountainous terrain.
Open-pit mining continued for a period after the war. However, as the available resources declined, mining operations eventually ended in 1965.
Today, the former industrial site has been transformed into a natural park where traces of the mining industry coexist with a remarkable wetland ecosystem.
A Rich Highland Ecosystem
Chatsubomi-goke Park forms part of the broader Yoshigadaira Wetlands, an area known for its remarkable biodiversity. Surveys across the wetland complex have recorded approximately 442 plant species, 20 animal species, 62 bird species, and 14 dragonfly species.
Wetland vegetation includes tussock grasses, bog cranberries, cotton grass, and Asian skunk cabbage. Various aquatic plants can also be found around natural ponds such as Hyohe Pond, Ōike Pond, and Mizu Pond.
Forest Green Tree Frogs at High Altitude
The surrounding wetlands are also an important breeding environment for the forest green tree frog, known in Japan as the moriaogaeru.
Breeding has been recorded at an elevation of approximately 2,150 meters, an exceptionally high altitude for this species in Japan. The area’s volcanic geothermal conditions and relatively warm groundwater may help create suitable breeding environments.
Because strongly acidic water supports relatively few fish, the frogs face fewer aquatic predators. They consequently display an unusual breeding behavior, attaching their distinctive egg masses to vegetation around the water rather than laying them directly in the water.
Rare wildlife, including birds of prey and Japanese serow, can also be found in the wider mountain environment, further contributing to the area’s ecological importance.
Combining Nature, History, and Hot Spring Travel
Chatsubomi-goke Park is located in the Kuni area, making it possible to combine a visit with a trip to nearby mountain hot springs such as Hanashiki Onsen and Shinyaki Onsen.
The relatively high elevation also provides a refreshing environment during the warmer months. Visitors can enjoy a walk through the park while learning about the relationship between volcanic activity, mineral springs, moss, and the region’s mining history.
For travelers exploring the wider Kusatsu and Kuni mountain area, the park offers a different experience from a traditional hot spring town. Instead of focusing on bathing culture, it reveals the geological and ecological forces that have shaped the region.
Panoramic Views from Shibu Pass
Another highlight of the surrounding area is Shibu Pass, located nearby along National Route 292. The pass is famous for the monument marking the highest point on Japan’s national highway network.
From this high mountain viewpoint, visitors can look down toward the Yoshigadaira Wetlands and see the contrast between the rugged volcanic landscape around Mount Kusatsu-Shirane and the soft green wetlands below.
The scenery changes dramatically with the seasons, from fresh spring greenery to summer vegetation, autumn grass colors, and snow-covered winter mountains.
A Natural and Industrial Heritage for the Future
Chatsubomi-goke Park is a place where three very different stories meet: the geological history of volcanoes, the industrial history of iron mining, and the ecological history of a rare wetland environment.
The vivid green Chatsubomi-goke growing in strongly acidic water is a striking reminder that life can adapt to environments that appear inhospitable to humans. At the same time, the former mining landscape illustrates how people once made use of the region’s unusual geological resources.
Today, conservation and responsible tourism are essential to protecting this fragile environment. Visitors are encouraged to follow designated paths and respect the natural surroundings so that the moss colony and its associated ecosystem can continue to be studied and appreciated.
Discover the Mysterious Green World of Chatsubomi-goke
Hidden deep in the mountains of Kuni, Chatsubomi-goke Park offers an extraordinary glimpse into the relationship between Earth and life. Acidic mineral water, volcanic geology, ancient iron formation, historic mining, and rare organisms have combined to create a landscape unlike most other tourist destinations in Japan.
For travelers interested in volcanoes, unusual ecosystems, industrial heritage, and Japan’s lesser-known natural landscapes, this remarkable park offers an experience that goes far beyond simply admiring a beautiful moss-covered valley.
Walking through the vivid green landscape of Chatsubomi-goke Park is an opportunity to encounter a rare world where the power of the volcano and the resilience of nature can be seen together.