Mount Haruna is a prominent mountain in northwestern Gunma Prefecture and one of the Three Mountains of Jomo, together with Mount Akagi and Mount Myogi. Revered as a sacred mountain since ancient times, it combines dramatic volcanic landscapes with rich natural scenery, history, and culture.
On the southwestern foothills stands the historic Haruna Shrine, which has long been an important center of mountain worship. At the summit area lies the beautiful Lake Haruna, with the graceful cone of Mount Haruna-Fuji rising beside it. Together, the lake and mountain form one of the most recognizable landscapes in Gunma.
Mount Haruna is a large complex volcano approximately 20 kilometers in diameter. A caldera measuring roughly 3 kilometers from east to west and 2 kilometers from north to south extends across the summit area, with Lake Haruna occupying part of the caldera.
Rising from the center of the lake is Mount Haruna-Fuji, a lava dome standing approximately 1,390.3 meters above sea level. Its beautifully symmetrical, conical shape is reminiscent of Mount Fuji, giving the mountain its name. The view of Haruna-Fuji reflected beyond the lake is one of the area’s most elegant scenic landscapes.
The caldera is surrounded by a series of distinctive peaks. The highest is Mount Kamongatake, at approximately 1,449 meters, followed by mountains including Mount Soma, Futatsudake, Mount Eboshidake, and Mount Binkushiyama.
Further outside the central caldera are parasitic volcanoes such as Mount Mizusawayama and Mount Mitsumine. These complex landforms were created through repeated volcanic activity over a very long period of time and give Mount Haruna its varied and dramatic profile.
Volcanic activity at Mount Haruna is thought to have begun approximately 500,000 years ago. Its geological history is generally divided into the Older Haruna Volcano and the Younger Haruna Volcano.
The Older Haruna Volcano remained active until around 240,000 years ago and formed a large stratovolcano. After a dormant period lasting roughly 200,000 years, volcanic activity resumed around 50,000 years ago.
During the activity of the Younger Haruna Volcano, enormous quantities of pumice and pyroclastic material were erupted, contributing to the formation of the present caldera. Later volcanic activity produced a series of lava domes, including the mountains now known as Mount Haruna-Fuji, Mount Soma, Mount Mizusawayama, and Futatsudake.
Many of these mountains are primarily composed of andesitic lava. Their complex forms are a direct result of the long and varied volcanic history that shaped the Haruna mountain range.
Among Mount Haruna’s many eruptions, particularly important events occurred between the 5th and 6th centuries, during Japan’s Kofun period.
Around 489, a large phreatomagmatic eruption known as the Futatsudake-Shibukawa eruption occurred. Volcanic ash and mudflows spread across a wide area, and the eruption is estimated to have reached Volcanic Explosivity Index (VEI) 4.
The eruption is thought to have had a significant impact on communities living in the surrounding region at the time.
Another, larger eruption occurred around the middle of the 6th century, producing large quantities of pumice and pyroclastic flows. Evidence of these eruptions has been discovered at numerous archaeological sites throughout Gunma.
In areas such as Shibukawa and Takasaki, several Kofun-period settlements and archaeological sites were buried by volcanic deposits. At the Kanai Higashiura Archaeological Site in Shibukawa, human remains caught in a pyroclastic flow have been discovered, providing important evidence of the destructive power of Mount Haruna’s eruptions during this period.
The slopes of Mount Haruna are deeply cut by valleys created through erosion over countless years. The Haruna River flows along the southwestern side of the mountain, the Haruna Shirakawa River runs to the southeast, and the Numao River flows toward the northeast.
These rivers have gradually carved their way through the mountain, creating deep valleys and varied terrain that contribute to the distinctive natural scenery of Mount Haruna.
Large alluvial fans have also developed around the foothills. Over long periods, gravel and sediment transported by volcanic activity and erosion accumulated to form these gently sloping landscapes.
Today, many of these areas support agricultural fields and settlements, providing an important foundation for local life around the mountain.
Mount Haruna has been regarded as a sacred mountain since ancient times. The most prominent symbol of this tradition is Haruna Shrine.
Surrounded by dramatic rock formations deep within the mountain, Haruna Shrine has long been one of the major sacred sites associated with mountain worship in the Kanto region. Its grounds combine historic buildings, enormous rocks, forests, and flowing water, creating a landscape where religious tradition and nature are closely intertwined.
Mount Haruna is also associated with numerous legends passed down through generations. One local folktale tells of the giant Daidarabotchi, who supposedly competed with Mount Fuji and Mount Asama to create the mountains.
Another legend says that the Buddhist monk Kukai, also known as Kobo Daishi, struck the ground with his staff and created a well.
Such stories reveal how Mount Haruna has long been connected not only with religious beliefs but also with the imagination and folklore of the people who have lived around the mountain.
Lake Haruna, located within the caldera of Mount Haruna, is surrounded by the Haruna Prefectural Park. Visitors can enjoy walking along the lakeshore as well as outdoor activities such as boating and camping.
The view of Mount Haruna-Fuji rising beyond the lake is one of the defining landscapes of Mount Haruna. The appearance of the lake and mountains changes with the seasons, making the area attractive throughout the year.
At the foot of Mount Haruna lies Ikaho Onsen, one of Gunma’s best-known hot spring destinations. The mountain can be reached from the hot spring town via Gunma Prefectural Route 33, and the drive offers beautiful mountain scenery along the way.
Combining a visit to Mount Haruna with a stay at the hot springs makes the area well suited to a leisurely road trip or sightseeing excursion.
Every year, from approximately late May to late June, Mount Haruna becomes colorful with blooming Japanese azaleas and flame azaleas.
The roads around Lake Haruna and the Numanohara area are particularly attractive during this season, when vivid red flowers contrast beautifully with the surrounding fresh green vegetation.
Visitors traveling to Mount Haruna in late spring or early summer can combine a walk along the lakeshore with a view of these seasonal flowers for a particularly scenic experience.
Mount Haruna offers a remarkable combination of dramatic volcanic terrain, beautiful Lake Haruna, the graceful cone of Mount Haruna-Fuji, and a collection of distinctive surrounding peaks.
At the same time, the mountain preserves evidence of ancient volcanic eruptions, archaeological sites dating from the Kofun period, centuries-old mountain worship, and the history and legends associated with Haruna Shrine.
Visitors can also enjoy a wide range of activities, including hiking, lakeside walks, scenic drives, hot springs, boating, and seasonal flower viewing.
With nature, volcanic history, religion, culture, and tourism all intertwined within one mountain region, Mount Haruna offers a fascinating glimpse into the natural and cultural heritage of Gunma. When visiting the area, take time to admire the scenery of Lake Haruna and Mount Haruna-Fuji while discovering the long geological and cultural history that has shaped this remarkable mountain.