Why Is This Giant Rock Here? A Long-Standing Geological Mystery
The biggest mystery surrounding Iwagami Flying Stone has always been its origin. When the rock was investigated in the early Showa period around the time of its designation as a Natural Monument, researchers believed that it had been transported from Mount Akagi by volcanic activity.
However, scientific methods for analyzing rocks were still developing at the time, and this theory was based largely on the rock’s appearance and mineral characteristics.
As geology and volcanology advanced, another possibility emerged: the Mount Asama origin theory. Mount Akagi is approximately 18 kilometers away in a straight line, while Mount Asama is about 51 kilometers away. Although Asama is much farther away, the volcanic mudflow deposits found around Maebashi show characteristics associated with Mount Asama.
This led researchers to investigate whether Iwagami Flying Stone might also have originated from Mount Asama.
The Maebashi Mudflow and the Discovery of Its Asama Origin
Central Maebashi is built on a diluvial plateau known as the Maebashi Plateau. The plateau consists largely of deposits from a massive volcanic mudflow that occurred approximately 24,000 years ago. This geological formation is known as the Maebashi Mudflow.
Research has shown that the mudflow was associated with the collapse of Mount Kurofu, part of the outer rim of Mount Asama. For many years, taking samples from Iwagami Flying Stone was difficult because of its status as a protected cultural property.
However, a three-year research project conducted from 2013 examined the rock using techniques including strontium isotope ratio analysis (87Sr/86Sr) and thermoluminescence dating.
The results disproved the earlier theory that the rock originated from Mount Akagi. Instead, scientific research demonstrated that Iwagami Flying Stone is a volcanic rock that was transported over a long distance by the Maebashi Mudflow approximately 24,000 years ago following a massive collapse of Mount Asama.
The mudflow traveled from the northern slopes of Mount Asama along the Agatsuma River and Tone River, eventually reaching the area around present-day central Maebashi. The enormous distance covered by the ancient mudflow provides a remarkable illustration of the power of natural forces in Japan’s volcanic landscape.
This research is also significant from the perspective of volcanic disaster prevention, as it provides valuable information about the scale and reach of ancient volcanic events.
Size and Geological Characteristics
Detailed surveying has revealed the impressive scale of Iwagami Flying Stone. Its height above ground is approximately 9.47 meters, while its exposed surface area is about 84 square meters. The visible portion has a volume of approximately 295 cubic meters.
Further investigation found that the rock extends approximately 8.5 meters underground. Its total volume is estimated at around 714 cubic meters, with an estimated total weight of approximately 2,098 tons.
The rock is composed of pyroxene andesite and has a distinctive reddish appearance. Because of this reddish-brown color, similar large volcanic rocks found throughout the Tone and Agatsuma River areas are collectively known as “Akaishi,” meaning “Red Stones.”
Individual rocks in the region also have their own local names, including Otsuya-no-Iwa and Tokeishi, reflecting the close relationship between these geological features and local traditions.
Legends of Curses and the History of Worship
Iwagami Flying Stone is surrounded by traditional stories that reflect the awe and fear it inspired among local people. According to the Maebashi Fudoki, a local record compiled in 1684, a stonemason once attempted to cut into the giant rock.
The legend says that when the mason struck the rock with a chisel, blood began to flow from the stone, and the stonemason subsequently died. Following this incident, local people are said to have begun worshipping the rock as a sacred entity, eventually leading to the establishment of Iwagami Inari Shrine.
This legend was also recorded in the application documents submitted when the rock was proposed for designation as a Natural Monument during the Showa period. These records demonstrate how deeply the giant rock was regarded as sacred by the local community.
Small shrines and stone altars can still be found around the rock today. Within the quiet grounds of Iwagami Inari Shrine, traditional worship continues alongside this remarkable geological monument.
A Unique Sightseeing Spot in Central Maebashi
Iwagami Flying Stone is located approximately 2.8 kilometers northwest of JR Maebashi Station, in an urban residential area of the city. Despite its surroundings, entering the shrine grounds reveals an enormous rock whose mysterious presence can feel surprisingly powerful.
For visitors, the site offers a rare opportunity to encounter evidence of ancient volcanic activity in the middle of an urban environment. Rather than requiring a trip deep into the mountains, travelers can see this extraordinary geological feature while exploring Maebashi itself.
The rock has also been recognized as a local landmark for generations. It was already known as a notable sight during the Meiji period, when postcards featuring the rock were produced.
Today, Iwagami Flying Stone offers an interesting combination of geology, natural history, folklore, religion, and local culture. It is a particularly fascinating destination for visitors interested in understanding how Japan’s landscape and traditional beliefs have developed together.
Where Ancient Nature and Human Faith Meet
Iwagami Flying Stone is much more than a giant boulder. It is a geological heritage site that preserves evidence of a massive volcanic disaster approximately 24,000 years ago, while also serving as a sacred place that has been respected by local communities for centuries.
Modern scientific research has revealed the remarkable journey of the rock, but understanding its geological origin has not diminished the sense of mystery surrounding it. Instead, science and traditional beliefs offer two different perspectives on the same extraordinary natural monument.
When visiting Maebashi, consider stopping at Iwagami Inari Shrine to see this remarkable stone for yourself. Standing quietly in the middle of the city, Iwagami Flying Stone provides a fascinating glimpse into both the immense forces that shaped Japan’s landscape and the enduring spiritual traditions of the people who live there.