The 1783 Great Eruption of Mount Asama
On July 8, 1783, according to the traditional Japanese calendar, Mount Asama experienced one of the most significant eruptions in its recorded history.
Volcanic activity had been increasing for several months, with underground rumbling becoming particularly intense in July. At around 10 a.m., a huge eruption sent flames and enormous quantities of volcanic material down the mountainside, including pyroclastic flows and lava.
A particularly devastating debris avalanche traveled northward and struck Kambara Village. The village was overwhelmed within a matter of minutes, causing extensive loss of life and leaving a lasting mark on the history of the region.
The lava that emerged during the final stage of the eruption eventually formed the landscape now known as Onioshidashi.
The Vast Onioshidashi Lava Field
The lava field extends approximately 5.5 kilometers in length and between 800 meters and 2 kilometers in width, covering an area of approximately 6.8 square kilometers.
Its unusual appearance is different from that of a smooth lava flow. The landscape consists of huge quantities of volcanic material that accumulated, partially melted, and moved during the explosive eruption.
The resulting field of jagged black and gray rocks resembles a vast natural sculpture. Walking among these formations gives visitors a vivid sense of the geological forces that shaped the Asama Highlands.
Why Is It Called “Onioshidashi”?
The exact origin of the name “Onioshidashi” is unknown. Historical documents indicate that people once believed that demons or “oni” lived on Mount Asama.
The violence of the eruption may have appeared as though a powerful demon had pushed enormous rocks out of the mountain. According to local tradition, this imagery eventually gave rise to the name “Onioshidashi,” which can be loosely interpreted as “the place where demons pushed out the rocks.”
Highlights of Onioshidashi Park
Asamayama Kannon-do Temple
At the center of the park stands Asamayama Kannon-do, a branch temple of Kan’eiji Temple in Ueno, Tokyo.
The temple was established in 1958 to commemorate and pray for the victims of the 1783 eruption. The temple enshrines Shō Kannon, a form of Kannon traditionally associated with compassion and protection.
The temple holds a special opening of its main hall on the 18th of each month, when visitors can pay their respects and experience an important aspect of the site’s spiritual character.
Walking Trails Through the Lava Field
Well-maintained walking paths lead through the rugged lava landscape, allowing visitors to explore the formations at close range.
On clear days, the surrounding scenery of Tsumagoi Village opens up beyond the lava field. Depending on weather conditions and visibility, distant mountain ranges including the Northern Alps, Tanigawa Mountain Range, and Mount Nantai may be visible.
Several walking routes are available, including paths leading toward the Okunoin approach and Enkō Kannon, as well as routes designed for observing alpine plants. Visitors can choose a course according to their available time and fitness level.
A Rich Habitat for Alpine Plants
The spaces between the lava rocks provide a surprisingly diverse habitat for alpine and highland plants.
From the appearance of fresh greenery in early May through early summer, visitors may see delicate plants such as Iwakaraga, Tsugazakura, Komakusa, and Rhododendron japonicum.
Seasonal Flowers Among the Volcanic Rocks
Hikarigoke, or luminous moss, can be observed from around May through late October. Under suitable conditions, the moss produces a mysterious greenish glow that contrasts beautifully with the dark volcanic rocks.
From around July, fireweed and other highland plants come into bloom. Their vivid flowers create striking contrasts against the black and gray lava.
Autumn colors begin to appear from around mid-September. The combination of red and yellow foliage with the rugged lava formations creates a particularly distinctive landscape.
The History of Onioshidashi Park
The area’s development as a tourist destination began in the early 20th century.
In 1919, Seibu Group founder Yasujiro Tsutsumi visited the area and recognized its potential as a scenic destination close to Karuizawa. During the 1920s, road improvements and bus services gradually made the area more accessible.
In 1935, an observation facility known as Iwakutsu Hall was constructed, further establishing the area as a tourist attraction.
On July 1, 1951, the site officially opened as what is now known as Onioshidashi Park. Improvements continued over the following decades, and the park developed into one of the signature attractions of the Asama Highlands.
The Geological Story of Mount Asama
Mount Asama is a stratovolcano that is believed to have begun its volcanic activity more than 100,000 years ago. It forms part of the volcanic zone of central Japan and has undergone repeated eruptions throughout its geological history.
The mountain has a complex volcanic structure involving peaks and volcanic bodies such as Mount Kurofu and Mount Maekake. Repeated volcanic activity gradually created the mountain landscape visible today.
The volcanic history of Mount Asama is therefore the fundamental reason why the extraordinary landscape of Onioshidashi exists.
Learning About the 1783 Eruption
Visitors who want to understand the human history behind the volcanic landscape can also visit the Tsumagoi Local History Museum, operated by Tsumagoi Village.
The museum presents information about the 1783 eruption, its impact on local communities, and the subsequent history of recovery and reconstruction.
A combination ticket for the museum and Onioshidashi Park is also available, providing an opportunity to explore both the geological landscape and the historical story of the disaster.
Four Seasons at Onioshidashi Park
Spring
Spring brings fresh greenery to the Asama Highlands. Alpine plants begin to emerge between the volcanic rocks, creating a fascinating contrast between new life and the barren lava landscape.
Summer
Summer is an excellent season for observing alpine plants. Flowers add color to the dark volcanic formations, while the highland environment offers refreshing scenery away from the heat of the lowlands.
Autumn
From around mid-September, the vegetation gradually turns red, orange, and gold. The colorful foliage surrounding the black lava rocks creates a landscape unlike a conventional autumn forest.
Winter
Snow can cover the lava field during winter, dramatically changing its appearance. The combination of snow and volcanic rocks creates another distinctive view of the Asama Highlands.
A Place Where Fire and Life Meet
Onioshidashi Park is more than a scenic viewpoint. It is a place where the geological history of Mount Asama, the memory of a devastating eruption, and the continuing cycle of natural life can all be experienced together.
The enormous lava field demonstrates the destructive force of volcanic activity, while the alpine plants growing in cracks and gaps between the rocks demonstrate nature’s ability to gradually reclaim even the harshest environments.
For international visitors, the park also provides an accessible introduction to Japan’s volcanic landscape and the relationship between local communities and the mountains that surround them.
Experiencing the Power of Nature
Walking through the rugged lava formations, looking toward Mount Asama, discovering alpine flowers among the rocks, and visiting the Kannon temple create an experience that combines nature, geology, history, and Japanese culture.
Onioshidashi Park is one of the most distinctive landscapes in the Asama Highlands, offering visitors a chance to walk through a vast natural monument created by one of Mount Asama’s most powerful eruptions.
Take your time exploring the walking trails and viewpoints, and experience the extraordinary landscape where volcanic fire, mountain scenery, and new life have come together over more than two centuries.