Onami Pond is an almost perfectly circular crater lake in the Kirishima Mountains, in the northeastern part of Kirishima City, Kagoshima Prefecture. It measures approximately 630 meters in diameter and has a circumference of about two kilometers. Formed by volcanic activity in the Kirishima Mountains, the lake was formerly also known as Ōnami-ike, using a different character for “wave.”
Onami Pond was formed approximately 40,000 years ago when water accumulated in a volcanic crater created by activity in the Kirishima Mountains. The lake is approximately 11.6 meters deep, and its beautiful surface has a dark blue-green color.
The water is exceptionally clear, allowing visitors to see down toward the lakebed. Although the water is strongly acidic, with a pH of approximately 5.20, crucian carp have been confirmed to live in the lake.
Onami Pond has no outlet river, giving it a quiet and mysterious atmosphere. The absence of flowing water adds to the sense of stillness that makes the lake such a distinctive feature of the Kirishima landscape.
Large quantities of pumice were ejected from the crater during volcanic activity. Some of this material remains in geological layers and is known as Iwaokoshi Pumice.
The surrounding volcanic mountain reaches an elevation of 1,412 meters, while the lake surface lies at an elevation of 1,241 meters. Onami Pond forms part of the beautiful natural scenery of the Kirishima mountain range.
A local legend also says that a divine dragon lives in the lake, and this story has long been passed down among the people of the region.
The hike to Onami Pond begins at the Onami Pond Trailhead on the southwestern side of the lake. The trailhead is located near the starting point of Miyazaki and Kagoshima Prefectural Route 1, the Kobayashi–Ebino Kōgen–Makizono Line, which connects Kirishima City with Kobayashi City in Miyazaki Prefecture.
From the trailhead, it takes approximately 40 minutes to reach the lake on foot. The hiking trail is maintained and paved with stone throughout, making it relatively easy to walk compared with rougher mountain paths.
A walking trail runs around the lake, and completing the circuit takes approximately two hours.
The surrounding landscape includes Miyama-kirishima azaleas and thickets of dwarf bamboo. These plants create a rich natural environment and make the walk enjoyable throughout the seasons.
During the hike, visitors can also enjoy views of Onami Pond from Mount Karakuni, as well as distant views of the magnificent Sakurajima volcano.
An emergency shelter was installed by Kirishima City at the Onami Pond Trailhead in fiscal year 2013. It can accommodate up to 29 people in an emergency.
A rest hut known as the Onami Pond Rest House was built by Kagoshima Prefecture in 1963 near the lake. However, according to an inspection conducted in 2015, the building had deteriorated with age and was no longer permitted to be used.
There is also the Karakuni-dake Emergency Shelter at the saddle between Onami Pond and Mount Karakuni. These facilities provide support for hikers and help protect their safety in the mountain area.
Onami Pond offers beautiful scenery throughout the year, with a different appearance in each season.
Autumn is one of the most popular times to visit. The surrounding trees, including maples and Japanese red pines, change color and create a vivid display of autumn foliage around the lake.
In winter, the surface of the lake can freeze, creating a beautiful and almost dreamlike landscape. Snow-covered scenery around the water adds to the mysterious atmosphere of this volcanic lake.
The natural beauty of the Kirishima Mountains and the changing seasonal colors make Onami Pond an appealing destination for hikers and sightseeing visitors alike.
On February 13, 1959, Mount Shinmoedake experienced a small explosive eruption. The following day, at 2:50 p.m., a major eruption occurred.
The eruption damaged a police radio relay station located approximately three kilometers northwest of the crater of Mount Shinmoedake. The relay station stood on the southern outer rim of the Onami Pond crater and was struck by volcanic rocks.
The former relay station has since been removed, and facilities operated by the Ministry of Land, Infrastructure, Transport and Tourism now occupy the site.
One explanation for the name Onami Pond is that it was inspired by the large waves that sometimes form on the lake’s surface. However, a more elaborate local legend is also told about the origin of the name.
Long ago, a married couple living in a nearby village had no children. They prayed to the mountain deity, and eventually they were blessed with a daughter whom they named Onami.
Onami grew into a beautiful young woman. When she reached the age of 18, she received many marriage proposals, but she turned them all down.
One night, she threw herself into a mountain pond. According to the legend, she was actually the incarnation of a dragon deity.
Because of this story, the pond came to be called “Onami’s Pond,” and the name gradually changed into “Onami Pond.” The legend adds a mystical dimension to the lake and remains part of the area’s local folklore.
Onami Pond is a beautiful crater lake and an important part of the natural landscape of the Kirishima Mountains. Visitors can enjoy hiking and walking around the lake while taking in the surrounding volcanic scenery.
The lake is also associated with local legends and historical events, giving it a cultural significance beyond its natural beauty. Its seasonal scenery and mysterious stories make it a memorable destination for anyone interested in nature and outdoor exploration.
For hikers and nature lovers visiting Kirishima, Onami Pond is well worth exploring. Before setting out, visitors should check the latest mountain conditions and any access restrictions.