A Dramatic Landscape Created by the Onioshidashi Lava Field
The Onioshidashi Lava Flow — A Landscape Shaped by a Volcano
The area known as Onioshidashi was formed by lava released during the Great Tenmei Eruption of Mount Asama on August 5, 1783.
The resulting lava field extends for approximately 5 kilometers in length and 1–2 kilometers in width. In some areas, the solidified lava reaches around 30 meters in thickness.
A huge volume of lava flowed rapidly from the area around Maekakeyama, near the volcano’s crater, spreading across an area of approximately 6.8 square kilometers. At the front of the flow, enormous masses of blocky lava accumulated to depths of more than 50 meters.
The rough, chaotic appearance of the rocks was said to resemble oni, the demons or ogres of Japanese folklore, pushing rocks outward. This gave rise to the name “Onioshidashi,” meaning roughly “the place where demons push out rocks.”
Today, the lava field is an important natural landscape where visitors can observe landforms created by volcanic activity and learn about the geology and natural environment of the northern slopes of Mount Asama.
Powerful Volcanic Terrain and New Life
The sight of the dark lava rocks stretching across the landscape is striking, but the seemingly harsh terrain is also home to a surprising variety of life.
Small alpine plants such as iwakagami, Hakusan rhododendron, and tsugazakura grow in cracks and gaps between the rocks. Visitors may also encounter birds such as meadow buntings and butterflies including the red-winged Apollo butterfly, known in Japanese as benihikage.
The contrast between the rugged black lava and delicate alpine plants is one of the distinctive beauties of the Asama Highlands.
During the seasons of fresh greenery and autumn foliage, the dark volcanic rocks stand out dramatically against the vivid colors of the surrounding vegetation, creating an especially memorable landscape.
Asama Northern Foot Visitor Center
The Asama Northern Foot Visitor Center serves as the gateway to Asama-en. Inside, exhibits explain the history of volcanic activity at Mount Asama, the formation of its distinctive terrain, and changes in vegetation using dioramas, displays, and interpretive materials.
The center features specimens of volcanic rocks, animal exhibits, and information panels introducing the natural environment around Mount Asama. These displays help visitors understand how volcanic activity has shaped the landscape they are about to explore.
A striking display of a golden eagle greets visitors at the entrance, symbolizing the rich natural environment of the Asama Highlands.
Guided explanations are also available from staff and volunteer supporters. Learning about the volcano and its surrounding ecosystem before setting out on the trails can make the walking experience even more meaningful.
Volcano Walk — Explore the Lava Fields on Foot
One of the highlights of Asama-en is the natural walking trail known as the Volcano Walk. The trail takes visitors directly into the Onioshidashi lava field created by the 1783 Tenmei eruption.
Several routes are available, taking approximately 25 to 80 minutes depending on the route, time available, and level of physical fitness.
As you walk, you can observe the rugged volcanic rocks at close range and gain a sense of the enormous power that once reshaped the landscape. Alpine plants growing in the gaps between the rocks add a delicate touch to the otherwise rugged surroundings.
The area is also suitable for nature observation. Depending on the season, visitors may see alpine flowers, wild birds, and butterflies living among the lava formations.
From elevated sections of the trail, there are impressive views of Mount Asama and the broad Asama Highlands. On clear days, the panorama may extend toward Kusatsu-Shirane, the Tanigawa mountain range, and even the distant peaks of the Northern Alps.
Sky Rock Trail — A Deeper Trekking Experience
For visitors seeking a more challenging adventure, Asama-en also offers the Sky Rock Trail, a trekking route approximately 6 kilometers long that passes through a Special Protection Zone of Joshin’etsukogen National Park.
The route explores the volcanic terrain on the northern side of Mount Asama, allowing hikers to observe a variety of landforms created by volcanic activity.
Along the trail, you may encounter lava flows, enormous volcanic rocks, crater-related landforms, and lava trees—impressions left when trees were surrounded or buried by flowing lava and the lava later solidified.
The route also passes through areas where alpine plant communities have adapted to the demanding volcanic environment, offering an opportunity to appreciate the remarkable diversity of life found around Mount Asama.
A Guided Experience in a Protected Natural Area
For safety reasons, the Sky Rock Trail requires participants to be accompanied by a certified Geopark guide. The guided format allows visitors to learn about the geological features, volcanic history, plants, and other natural characteristics of the area while trekking.
The trek takes approximately 3–4 hours and includes distinctive landscapes such as Butai Lava, making it a rewarding way to explore the less accessible volcanic terrain of the Mount Asama foothills.
Asama Park Field — Camping in the Mount Asama Highlands
Asama-en also includes the Asama Park Field auto campground, providing an opportunity to stay overnight in the natural surroundings of the Asama Highlands.
With Mount Asama rising nearby, campers can spend the daytime surrounded by forest, listening to birdsong and enjoying the cool highland air. After sunset, the clear atmosphere provides excellent conditions for enjoying the night sky.
Spending a night beneath the stars, away from the lights and noise of urban areas, offers a different way to experience the landscape of Mount Asama.
The History of Asama-en
Asama-en opened in 1963 as a tourism facility developed to allow visitors to enjoy the scenery around the northern foothills of Mount Asama.
Although the park is located in Tsumagoi Village, it was built on land owned by Naganohara Town and therefore operates as a park managed by Naganohara Town.
From the Asama Volcano Museum to the Visitor Center
The park formerly housed the Asama Volcano Museum, which introduced the volcanic activity and geology of Mount Asama. The museum closed in 2021, after which the facility was renovated and given a new role as the Asama Northern Foot Visitor Center.
Remembering Japan’s Motorcycle History
Asama-en also once housed the Asama Memorial Museum, which commemorated the Asama Volcano Race, a famous motorcycle race held in the area in 1955.
The museum was relocated to Kita-Karuizawa in 2021. The surrounding Mount Asama area nevertheless remains closely associated with the history of motorcycle culture and racing in Japan.
Experience the Power of Nature at the Foot of Mount Asama
Asama-en Park offers a rare opportunity to experience the powerful landscape created by Mount Asama’s volcanic activity while also discovering the plants and wildlife that have adapted to this rugged environment.
The contrast between the enormous black lava formations and delicate alpine vegetation is particularly striking. From the walking trails, visitors can also enjoy expansive views across the Asama Highlands and toward the surrounding mountain ranges.
Whether you choose a short nature walk, a longer trek, wildlife observation, or an overnight camping experience, Asama-en offers many ways to connect with the landscape.
For travelers exploring the northern foothills of Mount Asama, Asama-en is an excellent destination for experiencing the geological power, natural beauty, and outdoor appeal of the Asama Highlands in one place.