Lake Haruna

Lake Haruna is located on the west side of Mount Haruna, one of the three highest mountains in Japan. The lake is a caldera lake formed by the eruption of Mt. Haruna, and offers beautiful views of “Haruna Fuji,” the central crater hill. The lake is an attractive spot for outdoor enthusiasts, used for various leisure and sporting events, including the pleasure of touring the lake on a sightseeing boat, auto-camping, and hill-climb races.

The lake was created by the activities of the Haruna Volcano. With a circumference of 4.8 km and an elevation of 1100 m, it is surrounded by the beautiful Haruna mountain range. The area around Lake Haruna is “Prefectural Haruna Park” and is crowded with many tourists throughout the four seasons. Visitors can enjoy cycling, horse-drawn carriage rides around the lake, boating, camping, and ice fishing and wakasagi (smelt) fishing in winter.

Lake Haruna Hot Spring

Located on the shore of Lake Haruna at an elevation of 1100 meters at the foot of Mt. The hot spring water, which wells up from deep in the ground, is fine and smooth. It is used as a base for excursions throughout the four seasons and is also good for rest and relaxation. It is ideal for families, camps, conferences, and concerts.

Lake Haruna

Lake Haruna is located in western Gunma Prefecture. The lake is a crater lake formed in the caldera of Mt. Haruna and belongs to the Tone River as a water system. It has a circumference of about 4.8 kilometers, an area of about 1.2 square kilometers, and a maximum depth of about 12 to 15 meters.

The lake has been known as a symbolic landmark of Ueno Province since ancient times, and has been composed as “Ikaho no Numa” (“Swamp of Ikaho”) since the time of “Manyoshu” (The Anthology of Myriad Leaves). Together with Haruna Shrine, the lake became a place of pilgrimage for the Haruna Ko, a belief in rain-making mainly in the Kanto region from the Edo period (1603-1868) onward. From the Meiji period (1868-1912) onward, cultural figures who gathered at the nearby Ikaho Onsen resort wrote about the area in their literary works. Since the Taisho era (1912-1926), full-scale tourism development has been underway, and the area attracts more than one million tourists a year (as of 1987), making it one of Gunma Prefecture’s most popular tourist spots all year round.

Overview

Akagi (1827 meters above sea level), Haruna (1449 meters above sea level), and Myogi (1103 meters above sea level), all volcanoes located in Gunma Prefecture, are symbolic of the prefecture as the three Jomo Mountains. In particular, Mount Akagi and Mount Haruna, located east and west of Takasaki, Maebashi, and Shibukawa cities and across the Tone River, were formed as stratovolcanoes through active volcanic activity at the same time, and later erupted to form a caldera when their tops collapsed. Lakes exist at the top of each of these mountains: Onuma and Kakumanbuchi on Mount Akagi, and Lake Haruna on Mount Haruna. The water from Lake Haruna flows out of the crater rapids and becomes the Numao River, which eventually joins the Agatsuma River and pours into the Tone River. Part of the lake is used for agricultural purposes, and at an elevation of 1,084 meters, it is the second highest lake in Japan after Chuzenji Lake. In cold winters, the entire surface of the lake can freeze over.

Mt. Haruna has been repeatedly erupting at the same spot since about 500,000 years ago, and the caldera at its summit is surrounded by multiple outer rings of horseshoe-shaped mountains. An explosion about 220,000 years ago created a caldera with a diameter of about 3 kilometers, and the prototype of Lake Haruna was formed there. About 40,000 years ago, another eruption occurred within the caldera, forming a large caldera measuring 4 kilometers east to west and 2 kilometers north to south. It is believed that this caldera was once filled with a lake. Several eruptions followed, and Haruna-Fuji and other volcanoes were born. Part of the lake within the caldera was filled by volcanic ejecta, forming the present Lake Haruna.

In the Nara period (710-794), the name “Ikaho no Numa” was used in the Manyoshu (Anthology of Myriad Leaves) to refer to the area between present-day Takasaki and Mount Haruna. The lake became known to poets in the capital as a representative scenic spot in Ueno Province. In the Middle Ages, the lake became an object of worship, and from the Edo period (1603-1867) onward, it became a place where farmers in the Kanto region gathered to pray for rain. This was called “Haruna Ko,” and it was believed that rain would fall if people visited the Haruna Shrine to the south of Lake Haruna, filled bamboo tubes with spring water, brought it back home, and sprinkled it over their fields. According to a legend associated with this belief, the wife of a military commander in the Kanto region during the Warring States period followed her deceased husband into Lake Haruna and entered the lake, where she became a dragon god and fulfilled the wishes of the farmers.

In the Meiji Period (1868-1912), Lake Haruna became a gathering place for cultural figures at the Ikaho Hot Springs located north of the lake, and Lake Haruna was depicted in literature, paintings, and music by Takehisa Yumeji, Yosano Akiko, Takahama Kyoko, and others. In the Taisho era (1912-1926), Lake Haruna was designated as the first natural park in Gunma Prefecture, and the number of tourists increased rapidly. During the high-growth period, the lake attracted as many as 30,000 tourists a day, who enjoyed water sports and boating in the summer and skating and ice fishing in the winter. Souvenir shops lined the shores of the lake, hot springs were dug on the opposite shore, campgrounds and ski resorts were built on Haruna Fuji and Numanohara, and a cable car was constructed. In recent years, fireworks displays and illumination events have been held on the lake.

Topography

The lake is a crater lake formed in the caldera of Mt. The lake’s surface elevation is 1084 meters above sea level, and the water level fluctuates about 2 meters depending on the season.

The lake is approximately 1.3 kilometers in length and 1 kilometer in diameter. Its circumference is about 4.8 kilometers and its area is about 1.24 square kilometers. The water volume is approximately 12.2 million cubic meters. The lake is “gradient” or “nearly oval” in shape.

The bottom of the lake has steep slopes near the shore, but when the depth exceeds 10 meters, the lake becomes a gently sloping plain. The maximum depth is 14 meters to 12.6 meters, and the lake bottom is covered with diatom carcasses and diatomaceous mud.

The water temperature is 22 to 25 degrees Celsius near the lake surface in the summer and about 10 degrees Celsius near the lake bottom. In spring and fall, the water temperature is uniform. In winter, the lake is covered with 0.4 meters of ice from January to March.

The transparency of the water has decreased with the increase in tourism, and is approximately 4.2 meters in the spring and 1.9 meters in the fall.

Lake Haruna’s water flows out of the crater rapids that drain from the northeast of the lake as the Numao River, which joins the Agatsuma River, which in turn flows into the Pacific Ocean via the Tone River. Under the River Act, it is classified as a tertiary tributary of the Tone River, a first-class water system. It is also used for irrigation through separately constructed canals and tunnels.

Formation History

Mt. Haruna is a mountain that has repeatedly undergone quadruple volcanic activity within a narrow area. The base of the mountain body extends 28 kilometers by 22 kilometers in diameter. Its caldera has a concentric triple structure and is horseshoe-shaped with a chipped eastern side.

The first eruption occurred about 500,000 years ago, and together with the Tonegawa Tectonic Line, part of the Kashiwazaki Chiba Tectonic Line, it erupted at the same time as Akagi. At this time, it formed as a stratovolcano about 2,500 meters above sea level. It then grew for about 250,000 years to become a mountain called Paleo-Haruna Volcano. About 225,000 years ago, a major eruption occurred, blowing off the upper half of the mountain and forming a caldera about 4.5 km in diameter.

Within the caldera, a new stratovolcano was formed about 220,000 years ago, creating a caldera about 1,800 meters above sea level. Thereafter, volcanic activity subsided, and the caldera is believed to have been a lake for about 160,000 years.

About 42,000 years ago, volcanic activity became active again, and a lava dome was formed. This caldera measures approximately 4 km east to west and 2 km north to south, and corresponds to the outer rim of present-day Lake Haruna. At that time, the entire caldera was filled with water and a huge lake existed.

About 31,000 years ago, new volcanic activity occurred in the center of the caldera lake, forming Haruna Fuji (1,390.5 meters above sea level) and Hebenagatake (1,229 meters above sea level). Volcanic activity continued inside and outside the caldera, with the eruptions of Mount Soma (1411 meters above sea level), Mizusawayama (1194 meters above sea level), and Futatsudake (1343 meters above sea level) in the Kofun Period. These eruptions caused Lake Haruna to be reclaimed and formed its present shape.

Today, a marshy area called Numanohara extends on the southeast side of Lake Haruna, which is believed to be a remnant of the lake’s reclamation.

Lake Haruna and Beliefs

Lake Haruna and Religious Beliefs

Since ancient times, Lake Haruna has been worshipped as a place to pray for rain. In the “Man’yoshu (Commentary on the Man’yoshu)” by Senkaku (1203?-), it is suggested that “Ikahonuma (Lake Haruna)” was a place for praying for rain, and in the “Yoriin Dai-monjo Gyojyo Eshin” by the 14th century monk Yoriin (1323-1392), it is recorded that Yoriin himself visited Lake Haruna and offered rice to the lake, suggesting that Lake Haruna was a place for praying for rain during the Middle Ages. Lake Haruna was known as a place of worship for praying for rain during the Middle Ages.

From the mid-Edo period (1603-1868), the belief that rainfall would be brought to the lake spread, as people would visit the Haruna Shrine on Lake Haruna, fill bamboo tubes with water from a sacred spring, take them home, and sprinkle them over the rice fields. This belief was called “Haruna Ko,” and in farming villages in the Kanto region, representatives of the village carried bamboo tubes every year to pray for rain. During the Edo period, Hisamori Nakagawa’s wife recorded that when she visited the Ikaho hot springs and Lake Haruna, “It is said that when it rains near this swamp, it will rain.

In the southern part of Takasaki City, known as Kibe-cho, there is a legend that a princess from this area entered Lake Haruna during the Warring States period and became a water goddess, and people from Kibe were considered the best people to perform rain-making rituals. Deputies from other regions were also sent to Kibe to pray for rain.

Even today, the Haruna Ko (a group of people who carry bamboo pipes) is still practiced, and those who carry the pipes are required to bring them back to their villages without stopping to rest along the way. The method of carrying the bamboo tubes varies from region to region, but in some areas the tradition is still practiced today.

Various Events

The areas around Lake Haruna, especially the Haruna Plateau (Numanohara and Mayumigahara), Haruna Fuji, and the outer rim of the mountain range (Mt. Sabegatake, Mt. Eboshigatake, and Mt. Tenmoku) are crowded with tourists and activity enthusiasts all year round. In spring, the mountain azaleas, renge azaleas, and cherry blossoms are in full bloom. In summer, visitors can enjoy boating on Lake Haruna, sightseeing boats, and hiking and mountain climbing in the surrounding area. The Haruna Hill Climb in Takasaki, held in May, is particularly exciting, with more than 7,000 people (in 2016) entering the cycling competition (hill climb). 20,000 spectators gather in August for the Haruna Festival, which includes a lantern floating ceremony at Onuma-no-Misaki Shrine and a fireworks display over the lake. In autumn, the Haruna area’s representative agricultural product, pears, are harvested and the Haruna Pear Festival is held on the shores of Lake Haruna. In September, the Lake Haruna Marathon is held, with competitors competing on a circular course around the lake.

Lake Haruna is also a popular destination during the fall foliage season and winter sports in the winter. Because of its high elevation, the autumn foliage comes earlier than in surrounding areas, and is at its best from mid-October to a month or so later. In winter, the Lake Haruna Illumination Festa is held in December, with 550,000 lights beautifully illuminating the lake and attracting 130,000 visitors. From January to February, Lake Haruna freezes over, and visitors can enjoy go-cart rides on the ice, skating, and fishing for wakasagi (smelt). However, depending on the ice conditions, the lake may be off-limits. Bass fishing and wakasagi fishing also take place, making Lake Haruna an attractive place for fishing enthusiasts.

Lodging facilities, restaurants, and souvenir stores are located along the lakeside, allowing visitors to enjoy leisure activities and sightseeing. There is also a ropeway station to Haruna Fuji, facilities at Prefectural Haruna Park, and campgrounds. Various events can be enjoyed in the area surrounding Lake Haruna, and the scenery and pleasures of each of the four seasons are widespread.

Natural Environment

Water Quality

Lake Haruna is known for the clarity and beauty of its waters. Legend has it that, thanks to the Koshimoto crab, the lake water remains clear even when rain or muddy water flows in. In “Travels in Ikaho” by Yoshiaki Atobe (1658 - 1729), the water is described as being “clear and undisturbed, like the lake water at Hakone. This clarity is believed to be due to the topographical features of the lake’s surroundings and the purity of the spring water.

In the Meiji period (1868-1912), Lake Haruna had a reputation for its crystal clear waters. The transparency was recorded as 9.5 meters in 1906 and 6 meters in 1916, and the color of the lake water was described as “indigo and clear. At that time, there was only one inn called “Kohan-tei” on the lakeside, and the surrounding area was said to be quiet.

However, after the lake was designated as a prefectural natural park in 1924, development proceeded and the number of tourists increased rapidly. 30,000 tourists a day at most visited the lake during the high-growth period of the 1950s, and the lake’s environment was affected as its clarity dropped to 3 meters. Eutrophication of the lake was attributed to wastewater from inns and stores, which resulted in a drop in transparency.

To address this problem, the Lake Haruna Water Quality Management Center was established in 1981, and sewerage and other improvements were made. The Fisheries Cooperative Association also took steps to purify the water through the installation of carbon fiber. As a result, the water quality improved, and fireflies such as Genji fireflies began to appear in the lake. The condition of the lake water is regularly surveyed and passes environmental standards.

However, transparency fluctuates with the seasons. During the spring and fall, when the lake water is stagnant, clarity declines, while winter freezing and spring thawing allow the lake water to circulate, increasing clarity. Local volunteers clean the bottom of the lake, and a new attempt to green the lake bottom is being considered.

Plants

Because of the high elevation of Mt. Haruna, cherry and azalea blossoms bloom later than in the plains. However, compared to other mountains in Gunma Prefecture, Mt. Haruna is not a high mountain and has less snow, so the range of vegetation is not as extensive. The lakes are surrounded by steep slopes, mainly on the southeast side of Numanohara and the southern shore. These slopes are covered with deciduous broad-leaved trees such as Japanese maples, Japanese white osmanthus, and Japanese elm. Miyakozasa and Quercus crispula are also found, but in general they are not primary forests, but compensatory vegetation that has been affected by humans. The lakeside area has been damaged by human development.

The southeast swampy plain, which was once a lake, has transitioned from marshland to grassland and then to forest. Here, groups of yusuge and matsumisou can be seen. In particular, the yellow flowers of the yusuge, which bloom on summer evenings, are considered a symbol of Mount Haruna and Lake Haruna. Endangered species such as the kikyo, omina-esi, tin saiko, and korinka can also be seen in Numanohara. Past land reclamation and the construction of ski resorts have led to a dry transition from silver grass steppe to forest. The oak forests that cover the grasslands are the largest in the prefecture, and there is also a valuable hybrid species of oak and Quercus crispula called the “Japanese oak” (Quercus crispula).

The grasslands around the Shibukawa-Matsuida line on Gunma Prefectural Road No. 33 have been facing problems with invasion of non-native plants. In particular, the giant longhorn grass has been forming large populations along the sides of the road since 2000 and is a serious cause for concern.

Plants of special note on Mt. Haruna include Haruna yukizasa, Joshu kamomezuru (a variety of kobanokamomezuru), and Miyama funabarasou (a hybrid of funabarasou and kusa-tachibana).

Fish and shellfish

According to the Ministry of the Environment’s Basic Survey on the Conservation of the Natural Environment, Lake Haruna had 22 species of fish in 1987 and 11 species in 1993; the 11 species in 1995 ranked 37th among major lakes and marshes in Japan.

Wakasagi (smelt) and other specialty fish, rainbow trout (Oncorhynchus mykiss), Japanese cyprinid trout (Oncorhynchus mykiss), gengoro-buna (Herabuna), and carp species, which have increased due to planned releases, can be found in the lake. However, largemouth bass (black bass) and bluegill are non-native species brought in without permission, and the only original native species to Lake Haruna are loach and eels.

Amphibians and Reptiles

In the Lake Haruna area (Mt. Haruna), amphibians such as the mountain red-legged frog and the Azuma toad can be seen. Reptiles such as the striped snake, the mountain lizards, the blue-headed tree frog, and the Japanese pond skater, Jimguri, have been observed.

Birds

Lake Haruna is home to a variety of waterfowl, such as the great blue heron, least tern, and great egret in summer, and mallard ducks and teal in winter. On the shores of the lake and in the surrounding mountains, you can also see civets, cassowaries, cassowaries, sparrows, tanagers, chickadees, titmice, kookaburras, red-cockaded woodpeckers, Japanese bush warblers, Japanese nightingales, orioles, Siberian blue robins, Siberian blue robins, cuckoo, cuckoo-tailed godwit, and Japanese nightingale.

Mammals

The forests around Lake Haruna are home to a variety of mammals, including Japanese shrews, red mice, hares, foxes, raccoon dogs, weasels, martens, Japanese squirrels, Japanese flying squirrels, Japanese flying squirrels, flying squirrels, Japanese flying squirrels, Japanese flying squirrels, Japanese flying squirrels, Japanese flying squirrels, Japanese flying squirrels, and rabbit bats. In recent years, sightings of black bears and wild boars have been increasing.