Kitashiobara Village, Yamagata County, Fukushima Prefecture, Goshikinuma Nature Trail.
The Goshikinuma Pond Group, like Lake Hibara, was formed by the 1888 (Meiji 21) eruption of Mount Bandai. Among the approximately 300 ponds created by the rock debris avalanche, the ones with particularly diverse colors are collectively referred to as "Goshikinuma."
Among them, the pond that appears the bluest is the Aonuma.
First-time visitors are left speechless in front of this color. It is neither cobalt blue nor turquoise. It is a mysterious color with a deep blue within its transparency.
Tourist guidebooks and signs often say, "It is a beautiful blue pond." But—why is it blue?
"Beautiful" is just the beginning, let's take it a step further.
While there are many places known for the beauty of a single pond or lake throughout Japan, the only place where ponds within a hiking trail are adorned with various shades of blue is here at "Urabandai's Goshikinuma."
Stage 1: The Meeting of Two Waters
Aonuma receives two types of water flowing from upstream.
- One is acidic water flowing from the upstream Akaduma.
- The other is hot spring water (basic = alkaline) that springs from underground.
The water from Akaduma becomes strongly acidic due to mineral influences while passing through the ground of Mount Bandai. It meets the hot spring water (alkaline) that springs from underground at the downstream Aonuma.
The acidic and alkaline waters mix here.
Stage 2: The Birth of Nano-sized Particles
When acidic and alkaline waters mix, they are chemically "neutralized." This is the neutralization reaction learned in middle school science.
And what happens during the neutralization process? A certain chemical substance is born in the water.
The name of the substance is aluminum silicate. It is mainly composed of aluminum and silicon, and is known for its heat resistance, fire resistance, and excellent insulation properties, making it useful in construction materials, ceramics, fireproof materials, and electrical insulators.
This is the main character of the blue of Aonuma.
Stage 3: Only blue light is scattered.
These particles are floating in large quantities in the water. Sunlight shines down on them.
Sunlight contains all colors mixed together: red, orange, yellow, green, blue, indigo, and violet. These lights have different wavelengths. Red light has a longer wavelength, while blue light has a shorter wavelength.
And these particles have a property that strongly scatters short-wavelength light (= blue). Long-wavelength light (= red) passes through almost unchanged.
As a result, in the water of Aonuma, only blue light becomes easier for our eyes to reach. That's why it appears 'blue'.
Walking after knowing, Aonuma.
When we guide visitors at Aonuma, we initially do not explain anything and let them gaze at the pond. Most people say, 'It's beautiful.'
We slowly convey the story of the mixing of acidic water and hot spring water, and the story of aluminum silicate, while looking at the pond in front of us.
After the explanation, when they look at the pond again, the way they see it completely changes. Although it's the same blue, the depth is different. It changes from 'looking at the water' to 'seeing the physical phenomena occurring in the water'.
I don't think knowing science means looking at nature coldly. Rather, nature becomes more beautiful through knowledge. Aonuma is a place where you can truly feel that.
The other ponds in Goshikinuma also have different colors for various reasons.
In the Goshikinuma lake and pond group, there are several ponds with different shades besides Aonuma.
- Bishamon-numa ── The largest in Goshikinuma. It appears emerald green.
- Akanuma ── The water's edge is reddish-brown due to iron content.
- Midoronuma ── A rare pond where multiple colors mix, including green, red, and blue, depending on the location.
- Bentenuma ── A blue-toned pond, slightly lighter than Aonuma.
- Rurinuma ── A deep blue close to blue pond, referred to as lapis lazuli.
All of these colors are determined by the composition of the inflowing water, water depth, and surrounding geology. Walking the Goshikinuma Nature Trail allows you to see these ponds in order, and you can experience the diversity of nature through the "differences in color."
If you visit Aonuma
Access
It takes about an hour and a half to walk the Goshikinuma Nature Trail. It's a one-way path of about 3.6 km connecting the "Urabandai Visitor Center" and "Urabandai Kogen Station (Urabandai Product Center)." Aonuma is located on the west side of the trail (Product Center side).
Best Season
- Fresh Green (Late May to June): The contrast between the surrounding greenery and blue is vivid.
- Autumn Leaves (Mid-October to Early November): The contrast between autumn leaves and blue.
- Snowy Scenery (January to March): Aonuma surrounded by snow is particularly deep blue ★ Highly recommended.
It may come as a surprise, but the snowy season makes Aonuma the most beautiful, according to locals. The white background accentuates the blue.
Places to visit together
- Bishamonuma ── The entrance to the trail. A large pond of emerald green.
- Nakase-numa ── A unique landscape where a mountain floats in the middle of the swamp.
- Lake Hibara ── The largest lake in Urabandai created by the eruption in 1888. Beneath the lake lies the village of Hibara.
Would you like to embark on a journey to encounter stories?
At Tabinoito, guide Catherine, who has lived in Urabandai and Aizu for half a century, shares stories of the land that are not found in guidebooks, providing exclusive tours for one group per day.
We can also arrange a half-day course where you can leisurely walk along the Goshikinuma Nature Trail while explaining the reasons behind the colors of each swamp, tailored to your needs. You can leave all the long-distance driving and arrangements to us.
"I want to see nature through a scientific lens" or "I want to walk slowly with my spouse" ─ Whatever your requests, feel free to reach out. Just consulting is fine; we will not push you with persistent sales tactics.
👉 Get a free consultation via LINE:
https://page.line.me/tabinoito
👉 View travel plans for senior couples:
https://tabinoito.com/senior/
👉 View travel plans for filial piety:
https://tabinoito.com/oyakouko/
Related Articles:
The village submerged at the bottom of the lake ── Memories of Hibara village erased by the 1888 eruption of Mount Bandai
A hill floating in the swamp ── Memories of the 1888 eruption told by Nakase-numa and "Nagareyama"
Reference Materials
- Goshikinuma Lake Swamp Group (Mount Bandai Geopark)
- The mechanism of the colors of Goshikinuma (Qkamura Urabandai)
- Goshikinuma (Fukushima Prefecture)
- Goshikinuma (Wikipedia)
- Urabandai Visitor Center Local Exhibits and Interviews
- On-site coverage (Visit and interviews by Tabinoito guide, Catherine)
Author of this article
Catherine ── A guide who has lived in Fukushima's Urabandai and Aizu for half a century. Founder of the private tour company "Tabinoito." Deeply knowledgeable about the local nature, history, and cultural beliefs. We provide guided tours of Urabandai and Aizu, sharing stories of the land that are not found in guidebooks, limited to one group per day.
