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 rock debris avalanches, the ponds 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's neither cobalt blue nor turquoise. It has a mysterious hue 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 across Japan known for the beauty of a single pond or lake, the only place where ponds within a hiking trail are adorned with various shades of blue is here at "Goshikinuma in Urabandai."
Stage 1: The meeting of two waters.
It is said that two types of water flow into Aonuma from upstream.
- One is acidic water flowing from the upstream Akanuma.
- The other is hot spring water (basic = alkaline) that springs up from underground.
The water from Akanuma becomes strongly acidic due to the influence of minerals as it passes through the ground of Mount Bandai. This meets the hot spring water (alkaline) that springs up from underground at the downstream Aonuma.
Acidic and alkaline waters mix here.
Stage 2: Nanoparticles are born.
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 primarily composed of aluminum and silicon, and is known for its heat resistance, fire resistance, and excellent insulation properties, being utilized in building materials, ceramics, fireproof materials, and electrical insulators.
This is said to be the main character of Aonuma's blue.
Stage 3: Only blue light is scattered.
These particles are floating in large quantities in the water. Sunlight shines 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 long wavelength, while blue light has a short wavelength.
Moreover, 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 more accessible to our eyes. 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 will 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 finishing the explanation and looking at the pond again, the way the visitors see it completely changes. Although it is the same blue, the depth is different. It changes from 'looking at the water' to 'seeing the physical phenomena occurring in the water'.
I do not think that knowing science makes one view nature coldly. Rather, nature becomes more beautiful through knowledge. Aonuma is a place where you can truly feel that.
The other ponds of Goshikinuma also have different colors for various reasons.
In the Goshikinuma lake group, there are several ponds with different color tones besides Aonuma.
- Bijamonuma ── 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 bluish pond, but slightly lighter than Aonuma.
- Rurinuma ── A deep blue close to Aonuma, referred to as lapis lazuli color.
All of these colors are determined by the components of the inflowing water, water depth, and surrounding geology. Walking the Goshikinuma Nature Trail allows you to see these ponds in order, where you can truly 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. This is 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.
You might find it surprising, but I believe Aonuma in the snowy season is the most beautiful because the white background accentuates the blue.
Places to visit together
- Bishamonuma ── The entrance to the nature trail. A large pond of emerald green.
- Nakase-numa ── A unique landscape where a mountain flows in the middle of the swamp.
- Lake Hibara ── The largest lake in Urabandai created by the eruption in 1888. The village of Hibara sleeps at the bottom of the lake.
Would you like to join us on a journey to meet 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, offering tours limited to one group per day.
We can also create a half-day course where you can walk slowly along the Goshikinuma Nature Trail while explaining the reasons for the colors of each swamp, tailored to your requests. Leave all the long-distance driving and arrangements to us.
"I want to see nature from a scientific perspective" or "I want to walk slowly as a couple" ─ Whatever your request, feel free to ask. Just a consultation is also OK; we will not pressure 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:
A village sunk 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 (Bandai-san 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 Prefecture, Urabandai, and Aizu for half a century. Founder of the private tour company "Tabinoito." Deeply knowledgeable about local nature, history, and cultural beliefs. Offering guided tours of Urabandai and Aizu while sharing stories of the land that are not found in guidebooks, limited to one group per day.
