Mount Fuji

Japanese: 富士山 - ふじさん

It is a stratovolcano, mainly composed of basalt, that straddles Yamanashi and Shizuoka prefectures. It was once the main peak of the Fuji volcanic belt, but due to its beautiful appearance and the highest elevation in Japan (3,776 meters), it has been revered and loved as a symbol of Japan since ancient times, and is an active volcano well known overseas as well. Its slope is 32-35 degrees at the summit and 2-3 degrees at the base, forming a beautiful logarithmic curve, and its base diameter is about 35 kilometers east-west and 38 kilometers north-south.

In the past, it was written as "Fujin," "Fuji," or "Fuji," and some say it originates from the Ainu word "Fuchi" (fire). It is the main feature of Fuji-Hakone-Izu National Park (designated in 1936), and has been designated as a Special Place of Scenic Beauty along with Mount Unzen in Nagasaki Prefecture. It spreads out on all four sides, but on the northern foot of the mountain, between the surrounding mountains such as the Misaka mountain range, there are the Fuji Five Lakes (Yamanaka, Kawaguchi, Sai, Shoji, and Motosu), which were formed by lava flows from Mount Fuji, and tourism development has progressed, so there are many visitors throughout the year. It is one of the three most famous mountains in Japan (the others are Mount Tateyama and Mount Hakusan).

[Akira Suwa and Setsya Nakata]

Origins and background

Mt. Fuji is the highest mountain in Japan, but beneath it lie two old volcanoes, Senkomitake and Komitake, which were formed hundreds of thousands of years ago. Mt. Fuji itself is made up of two volcanoes, Old Fuji and New Fuji, with New Fuji volcano becoming active about 10,000 years ago. The maximum thickness of the ejecta is less than 1,500 meters. In other words, the Mt. Fuji we see is a stratovolcano formed by the overlapping of multiple volcanoes. Furthermore, Mt. Fuji is a relatively young volcano, and although it has not erupted for the past 300 years, it is believed that it will definitely erupt again in the future, so we must not let our guard down.

Mount Fuji is located in a unique location behind the base of the Izu Peninsula where the Philippine Sea Plate is colliding with the Japanese archipelago. The Misaka Series, a stratum made of submarine volcanic ejecta from about 25 to 20 million years ago (Miocene Epoch), is the base of Komitake and the contemporary Ashitaka volcano. Part of the Komitake volcano is exposed near Komitake (5th Station), the end point of the Fuji Subaru Line mountain road from Lake Kawaguchi. The Old Fuji volcano began activity about 80,000 years ago, and repeatedly erupted violently, dropping basaltic volcanic ash in southern Kanto and depositing the "Kanto Loam" (more precisely, Tachikawa Loam and Musashino Loam), which forms the plateau of the Keihin region. The volcanic ash near Tokyo is so fine that the individual grains are difficult to distinguish with the naked eye, and the layers are several meters thick, but if you follow it toward Mount Fuji, the grains gradually become coarser and the layers get thicker. In Gotemba and Subashiri on the eastern foot of the mountain, layers of coarse-grained brown volcanic gravel overlap to form layers several tens of meters thick.

Additionally, deposits from mountain collapses that occurred tens of thousands of years ago (debris avalanche deposits) have been found at the foot of Mt. Fuji. These are called "Old Fuji Mudflows" and form the surface of the Old Fuji Volcano. About 10,000 years ago, when the Pleistocene period was passing into the present day, this Old Fuji volcano experienced a sudden change in its eruptive activity. After that, for about 1,000 years, there were repeated eruptions that mainly spilled large amounts of lava in all directions, and the original shape of Mt. Fuji as we see it today was almost complete. These lavas include the Saruhashi Lava, Iwabuchi Lava, and Mishima Lava, which flowed down 30 to 40 kilometers from the central crater. A small part of Old Mount Fuji is exposed as "Akaiwa" (approximately 2,700 meters above sea level) in the crater created by the major eruption in 1707 (the 4th year of the Hoei era).

The New Fuji Volcano began to be active about 10,000 years ago. The New Fuji Volcano had been erupting frequently up until the Hoei eruption mentioned above, and had been growing while covering the Old Fuji Volcano with pyroclastic debris and lava from the explosions. However, about 2,500 years ago, a mountain collapsed on the eastern slope, depositing the Gotemba Mudflow. There are more than 60 parasitic volcanoes and parasitic craters on the mountainside from the summit, many of which are distributed in a north-northwest to south-southeast direction (the strike of the Fuji volcanic belt) that passes through the summit. In addition, the wind holes and ice caves distributed at the foot of the mountain are part of lava tunnels formed when basaltic lava flows. The Fuji Five Lakes were formed when basaltic lava dammed up rivers. Groundwater from Mount Fuji also springs up from the bottom of the lakes, but there are no natural drainage outlets except for Lake Yamanaka, and the water level fluctuates quite drastically. Furthermore, there are various legends about the appearance of Mount Fuji, such as one that says that in the 5th year of the reign of Emperor Korei, the 7th emperor, a huge collapse occurred overnight, creating Lake Biwa, and at the same time, Mount Fuji was born from a great uplift. However, this is scientifically unreasonable and contrary to the facts.

[Akira Suwa and Setsya Nakata]

Historical eruptions

The eruptive activity of Shin-Fuji volcano was particularly vigorous and repeated up until the Heian period (approximately from the end of the 8th century to the end of the 12th century). The oldest record of an eruption is found in a long poem, "A Song for Mount Fuji," said to have been written by the Man'yo poet Takahashi Mushimaro, which contains the lines, "The burning fire is put out with snow, the falling snow is put out with fire," and is believed to have been an eruption around 720 AD during the Yoro era (717-724). There are about 10 eruptions recorded in historical records, starting with the first in 781 (Ten'o 1), which is recorded in the Shoku Nihongi, followed by three major eruptions in 800 (Enryaku 19), 864 (Jogan 6), and 1707 (Hoei 4).

Until 1083 (Eiho 3), eruptions occurred about every 30 years on average, but in the six centuries leading up to the great eruption of 1707, there were only three eruptions, and after the 1083 eruption, no eruptions were seen for about 300 years. Furthermore, about 300 years had passed since the great eruption of 1707. Moreover, the eruptions up until 1083 were generally vigorous, and often produced lava flows, but after that, eruptions were limited to eruptions that emitted volcanic ash, and in terms of scale, there were no significant eruptions except for 1707. Furthermore, many documents, such as Miyako no Yoshika's "Fujisan-ki" in "Honcho Monzui" and "The Tale of the Bamboo Cutter," whose author is unknown, suggest that Mount Fuji continued to emit smoke for a long time even in historical times. It was after the aforementioned eruption of 1083 that the volcanic activity began to decline dramatically. Nevertheless, it appears that there was some continuous erupting of smoke for about a century after that, as can be seen from sources such as Saigyo's Sankashu, but Abutsu-ni's Izayoi Nikki and other sources indicate that the smoke completely ceased between the Heian and Kamakura periods.

According to the Nihon Koki and Nihon Kiryaku, the great eruption in 800 caused vigorous explosions and lava flows on the summit and slopes of the mountain, bringing about major changes in the transportation culture of the Tokaido and southern Kanto region. The Tokaido's Ashigara Road was blocked by a large amount of ash and sand, so the Hakone Road was opened in 802. The Ashigara Road was reopened in 803, but was overshadowed by the Hakone Road until the Tomei Expressway was built. Lake Utsu, located at the northeastern foot of the mountain, was divided by Takamarubi, a lava flow from the great eruption. Lake Yamanaka remains, but the lakes in the Oshino region flowed out as the Katsura River, and dried up, leaving behind the Oshino Hakkai, a nationally designated natural monument. The mountainside eruptions of 864-866 are recorded in the Sandai Jitsuroku and other records, but the intensity of the activity can also be inferred from geological surveys. It was the largest eruption in the recorded history of Mount Fuji, producing large lava flows such as Aokigahara and Kenmarubi, the former of which divided Senoumi on the northern foot into Lake Sai and Lake Shoji. According to drilling surveys, the volume of ejecta at this time appears to have exceeded that of the Hoei eruption.

The great eruption of 1707 was limited to violent explosive activity on the mountainside. First, dacite volcanic ash, pumice and obsidian erupted, the first time in about 2,500 years that Mt. Fuji had erupted, followed by basaltic volcanic ash and pyroclastic materials. The total volume of erupted material was about 1.7 billion cubic meters (equivalent to 680 million cubic meters of magma), and volcanic ash piled up about 5 centimeters thick in Kawasaki, about 90 kilometers to the east. The situation at the time is described in Arai Hakuseki's "Oritaku Shiba no Ki" and other works. In Edo, strong earthquakes, rumbling, explosions and air vibrations were felt repeatedly, black clouds covered the sky, and several hours after the eruption began, gray-white ash was followed by gray-black ash, and lights were used even during the day. In Edo, ashfall continued for more than 10 days, and the falling and accumulated volcanic ash was blown up by the wind, causing a respiratory epidemic throughout the Kanto region. 49 days before the Hoei eruption, there was a magnitude 8.7 earthquake (the Hoei Tokai earthquake).

[Akira Suwa and Setsya Nakata]

Current status and future of volcanoes

At the peak of Mt. Fuji, there is a crater with a diameter of about 800 meters, a circumference of about 3.5 kilometers, and a depth of over 200 meters, called the "Nain." The rim of the crater is called the "Ohachi" (bowl). To the southwest is Kengamine, the highest point in Japan at 3,776 meters above sea level, and to the north is Hakusan-dake at 3,756 meters above sea level. From Kengamine to the east, the mountains Mishima-dake, Komagatake, Joju-dake, Dainichi-dake, Kusushi (Yakushi-dake), and Hakusan-dake surround the crater in a string like a rosary. The "circumnavigation of the crater's rim" is about 4 kilometers, and takes nearly an hour and a half.

Kengamine is home to the Mount Fuji Weather Station, which was established in 1936 (Showa 11), and is an important base for meteorological observation in Japan, with a radar with a maximum detection range of 800 kilometers. As satellite observation became more widespread, the station was abolished in October 2004 (Heisei 16), and in 2008 it became the Mount Fuji Special Regional Meteorological Observatory (unmanned). The average annual temperature is -6.5°C, with a previous minimum of -38.0°C and a previous maximum of 17.8°C, and snow can fall even in summer. The previous maximum wind speed was 72.5 meters per second, and in winter, blizzards often continue with strong winds of over 20 meters per second for days on end. The amount of oxygen and air pressure are about two-thirds that of the plains, and water boils at about 88-87°C. The annual precipitation on the entire Mount Fuji is estimated to be about 2 billion cubic meters (about 20% of which comes from snowfall), but there is very little spring water on the mountainside. This is because the lava flows and pyroclastic material layers that make up the new Fuji volcano are porous, allowing water to seep deep underground. This underground water flows down along the top of the impermeable mudflow deposits that make up the surface of the old Fuji volcano, and springs up at Shiraito Falls, the bottom of the Fuji Five Lakes, and Oshino Hakkai at the foot of the mountain, and the abundant spring water in Gotemba, Mishima, Fujinomiya, and other cities is helping to develop local industries. Obtaining groundwater on the mountainside is the key to full-scale development of Mount Fuji. However, a network of automobile roads has been developed from the foot of the mountain to the middle slope (the fifth station on the north side and the new fifth station on the south side), and tourism development has progressed dramatically, making it more difficult to balance this with nature conservation and disaster prevention. There are also training grounds for the Self-Defense Forces and the U.S. military at the foot of the mountain.

Because Mount Fuji is the object of national interest, even after the Second World War, reports of abnormal phenomena such as the emission of smoke, rising ground temperatures, and active fumarolic activity were frequently reported. However, in reality, these were cases where dust blown up by strong winds or whirlwinds was mistaken for smoke, or where snow was blown away by strong winds or avalanches, exposing the ground in places, and these were simply assumed to be due to rising ground temperatures or active fumarolic activity. The temperatures of the fumarolic and geothermal areas scattered around the mountain, such as Aramaki on the summit of Mt. Joju, the Hoei Crater on the mountainside, and the third station at the Subashiriguchi volcano, have also dropped considerably in recent years, and volcanic earthquakes are occasionally observed.

Since the autumn of 2002, a series of low-frequency earthquakes have occurred with their epicenters at a depth of about 15 kilometers underground in the northeast part of the summit, and disaster prevention measures have begun to be taken. National and local governments have also created hazard maps for Mt. Fuji and started to conduct disaster prevention drills. Immediately after the magnitude 9.0 Tohoku Pacific Ocean Earthquake on March 11, 2011, a magnitude 6.4 earthquake occurred on March 15 with its epicenter at a depth of about 10 kilometers directly beneath Mt. Fuji. Seismic activity continued for a year after that, although it weakened, but no other phenomena that could be a precursor to an eruption were observed. Mt. Fuji is being monitored by the National Research Institute for Earth Science and Disaster Prevention, the Geospatial Information Authority of Japan, the Japan Meteorological Agency, the University of Tokyo, Yamanashi Prefecture, and others, using seismometers and GPS (Global Positioning System). In addition, various observation networks of related organizations have been established in the vicinity in preparation for the Tokai earthquake. In addition, the National Institute of Advanced Industrial Science and Technology, the University of Tokyo, Nihon University, and others are actively conducting research to decipher Mount Fuji's past eruption history.

[Akira Suwa and Setsya Nakata]

Collapse of the mountain

The most serious problem of Mt. Fuji is the collapse of slopes caused by weathering and erosion. The area above 2,450 meters above sea level is exposed rock, and weathering is progressing. Also, many streams (radiating valleys) have developed on the mountainside, such as "Osawa" on the west side and "Yoshida Osawa" on the northeast side. In particular, the former "Osawa Kuzure" is a huge valley about 10 kilometers long, 500 meters wide at its widest, and 150 meters deep, reaching from the foot of the mountain to Kengamine. Slope collapses continue. In the summer of 1980 (Showa 55), a group of several hundred people descending the Yoshidaguchi trail "Sunabashiri" was hit by a group of falling rocks at Yoshida Osawa, killing 12 people and injuring 31. Slope collapses are spreading rapidly on the eastern slope of the mountain. Disaster prevention works are being carried out to address this problem, but no fundamental measures have been taken, and it is truly an incurable disease (of Fuji).

There are also triangulation points on the summit of Mt. Fuji, one on the south side of Mt. Kengamine and the other on the north side of Mt. Hakusan. The former is the highest peak in Japan, but its altitude has dropped with each re-survey since it was officially measured at 3,778 meters in 1885 (Meiji 18) after the Meiji Restoration. A survey in 1926 (Taisho 15) measured 3,776.29 meters, which is the basis for the currently widely known 3,776 meters. Later, rocks on the summit collapsed, making the triangulation point marker dangerous, so after World War II in 1962 (Showa 37), the marker was lowered and reburied, making the altitude 3,775.63 meters. If it had been rounded up or down, it would have been the same as before, and there would have been no need to correct the atlas, but in fact it was tampered with and concreted to make it look like that. A similar operation was carried out again in 1977, and the altitude has remained at 3,776 meters. The Geospatial Information Authority of Japan also appears to be struggling terribly.

[Akira Suwa]

Vegetation

In terms of flora, Mount Fuji is unique among the mountainous regions of central Japan, with taxa such as Rhododendron candida, Orchidaceae, Amagikanaoi, Kanadei, and Fujizakura, which are endemic to the region. For this reason, it is included in the Fossa Magna region, along with Hakone and the Izu Islands, in the classification of Japanese flora. Furthermore, elements thought to be relict distributions, such as Hedysarum membranaceum and Purple Mensandra, can be found in the volcanic gravel areas. However, there are still many unknowns regarding the formation of the flora, such as the absence of Pinus pumila, which is distributed in the surrounding high mountains.

In terms of vegetation, the southern foot of the mountain has the steepest elevation gradient in Japan from the coast to the 3,776-meter summit, with a well-developed vertical distribution zone. From the coast to an elevation of around 800 meters, the area is covered with warm temperate (hilly) evergreen broadleaf forests, and below 400 meters there are forests of Machilus thunbergii and Castanopsis sieboldii, with the upper part transitioning to red oak forests. However, due to human destruction, natural vegetation can only be seen in fragments in this area, and most of the area is residential areas, plantations of cedar and cypress trees, Self-Defense Force training grounds, and Japanese silver grassland used as grazing land.

From 800 to 1600 meters, the area is a cool temperate (mountain) deciduous broadleaf forest. In this area, 800 to 1000 meters above sea level, which corresponds to the transition between the cool temperate and warm temperate zones, there are several lava flows called Marubi. All of these lava flows erupted 1000 to 1500 years ago, and today, forests dominated by conifers such as hemlock, cypress, and red pine have developed. Aokigahara Marubi, known as a sea of trees, is one of the largest of these, and is a forest mainly made up of hemlock and cypress, stretching 8 kilometers from east to west and 6 kilometers from north to south. Takamarubi in Oshino is also unique, with a spruce forest developing there. These two areas are designated as national natural monuments as the "Mt. Fuji Primeval Forest" and the "Oshino Hakkai" respectively. In other areas with well-developed soil, beech trees dominate, with some silver fir also found in deciduous broadleaf forests.

Above 1,600 meters is subalpine (subarctic, temperate) evergreen coniferous forest. In the case of Mt. Fuji, the lower part of the subalpine zone is dominated by Tsuga diversifolia, and the upper part by Abies mariesii (particularly in the upper part, larch and Betula ermanii are abundant, with some Abies mariesii mixed in). The tree line is approximately 2,500 meters, and the tree height of Betula ermanii, Alnus alpinus, and Alnus montana gradually decreases to border the limit. Around Oniwa and the Hoei crater, larch creeping trees appear above the tree line. Further above that is alpine volcanic barren land vegetation, with scattered species such as Japanese knotweed, Japanese knotweed, and Fujihatazao.

On the eastern slope, from Gotemba to Subashiri, vegetation was destroyed by the eruption of the crater (Hoei Crater) in 1707 (4th year of the Hoei Era), and the subsequent substrate is unstable, being scoria (rock scaly), so the progress of succession has been slow in areas above 1,300 meters, and volcanic barren vegetation, including scattered species such as Japanese knotweed and Japanese knotweed, still prevails, presenting a unique alpine landscape. On the other hand, species that make up the vegetation of the upper subalpine zone, such as mountain alder, mountain willow, and Erman's birch, have descended onto this bare land, and communities that make up each stage of succession are arranged in bands from this bare land toward the forest that has developed on the stable slope. In this way, vertical plant distribution zones with different development stages due to differences in the rate of vegetation succession and a mosaic structure of vegetation are often seen on Mt. Fuji.

[Masahiko Osawa]

Fauna

The fauna of Mount Fuji is typical of the central Honshu mountain range, with some cold-climate elements such as stoats, shrews, and nutcrackers added to Japan's temperate elements. The area around Subashiri on the east side of Mount Fuji is one of the leading bird breeding grounds in eastern Japan and is known as the birthplace of bird watching events. The foothills here are home to the copper pheasant, nightjar, black thrush, Japanese bush warbler, and treecreeper, while the subalpine zone is home to the common nutcracker, Japanese green pigeon, white-streaked pheasant, copper pheasant, and robin, while the Japanese bush warbler and rock lark can be seen near the tree line. The abundance of birds is similar in the forest area that stretches from Aokigahara to the fifth station of the Yoshidaguchi trail via the Shojiguchi trail, and this narrow, old-growth forest is one of Japan's leading treasure troves of forest bats. In addition to cave-dwelling species such as the lesser horseshoe bat, the greater horseshoe bat, and the bunny bat, tree-dwelling species such as the Fujian long-eared bat, the Kaguya bat, the brown bat, and the Japanese long-eared bat can be seen here, and it has also been confirmed that the Oze long-eared bat, which was thought to be endemic to Oze, also resides here.

There is a wide variety of other animals in this area, including Japanese serows, stoats, Japanese bush warblers, shrews, squirrels, flying squirrels, and dormice in the subalpine zone, and Fujimizura moles, Japanese bush mice, Japanese bush rats, Japanese house mice, Japanese ground mice, Japanese white spotted rats, Japanese common toads, and Fuji green grasshoppers in the upper part of the low mountain zone, as well as flying squirrels and Asiatic black bears. The grasslands at the foot of the mountain are home to Kobe moles, voles, Japanese harvest mice, hares, wild boars, stonechat, warblers, Japanese white butterflies, and mountain oak butterflies, and deer can be seen in the forests at Omiyaguchi, where there is a watering hole. Areas above 2,500 meters above sea level are considered alpine zones, but lowland or low mountain species such as field voles, Japanese field mice, Japanese house mice, and dormice also make their way up here, and outside of the climbing season wild boars, Japanese serows, Asiatic black bears, foxes, and martens can also be seen on the way to the mountain peaks.

However, animals thought to be alpine animals in Honshu, such as the Japanese field mouse, the Japanese shrew, the rock ptarmigan (seven were released in 1960 but have since disappeared), and the alpine butterflies Takane Hikage, Takane Kimadaraseri, Kohiodoshi, and Kumomatsumaki, do not live on Mt. Fuji. Also, the Japanese water mole, the Tohoku hare, the western Japan Smith's mouse, and the northern Japan Tohoku field mouse, which are found on the Japan Sea side of Honshu and northward, are not seen on Mt. Ashitaka. Monkeys that are not found on Mt. Fuji itself, and the warm temperate Kirishima green grass butterfly live on Mt. Fuji. Many animals on Mt. Fuji bear the name Fuji, such as the Fuji green grass butterfly and the Fuji yellow band, but there are also many animals whose scientific names are related to Fuji, such as the Japanese long-eared bat and a subspecies of the northern goshawk. However, no species are known to be endemic to this mountain.

[Yoshinori Imaizumi]

Mountaineering

There are theories that Prince Shotoku or En no Ozunu was the first to climb Mount Fuji, and it is thought that climbing was already popular around the 9th century, but this is not certain. There is an article that Matsudai Shonin of Suruga Province (Shizuoka Prefecture) built a temple on the summit in 1149 (Kyuan 5), and it is said that people climbed the mountain from the Murayama entrance. In the early modern period, Hasegawa Kakugyo (1541-1646) established a Fuji-ko sect, and people dressed in white robes led by guides climbed the mountain while chanting "Six Roots Cleansed." Fujiyoshida at the foot of the mountain is a temple town of Sengen Shrine, and developed as Japan's leading religious climbing site and a gathering place for climbers. The Fujinomiya trailhead is the main entrance, with the Yoshida, Gotemba, and Subashiri trails being the most commonly used, and the Murayama and Suyama trails having since been abandoned. Women were considered unclean, and could only climb up to the second station, Ko-Asamakami no Okama, at the Yoshida trailhead, and up to the first station, Nyonin-do, at the Murayama trailhead, but in 1866 (Keio 2), Mrs. Parkes, the British envoy to Japan, became the first woman to climb the mountain.

The mountain is open from July 1st until the fire festival on August 26th, but in recent years it is open until August 31st, and mountain huts at each trailhead are also open. At peak times, there are nearly one million climbers during this period, but since the Subaru Line toll road was opened from Kawaguchiko to the fifth station at the Yoshidaguchi entrance in 1964 (Showa 39), and the Omote Fuji Tour Road was built to the fifth station at the Gotembaguchi entrance in 1970, the mountain trail from the foot of the mountain to the fifth station has become deserted. There are also hikes around the crater at the summit, such as the Ohachi-meguri, which goes around the crater, and the Onaka-michi-meguri, which goes around the fifth station. In 1871 (Meiji 4), British Lieutenant Bayard climbed the mountain for the first time during the snowy season, and in 1895, Nonaka Itaru, a pioneer of high-altitude meteorological observation in Japan, climbed the mountain in the middle of winter for meteorological observation. Because Mt. Fuji is an independent high mountain, it is covered with blue ice in winter, making it a stage for snow and ice climbing, and many alpinists visit it. However, because it is the highest mountain in Japan, many people suffer from altitude sickness such as dizziness and headaches, and there are also many accidents caused by sudden wind gusts and avalanches in winter, so caution is required.

[Tokuhisa Kyuuou]

Folklore and Beliefs

The beautiful appearance of Mt. Fuji has been incorporated into many literary works and travel writings, including the "Manyoshu" and "The Tale of the Bamboo Cutter," and has also been depicted in paintings. The "Hitachi no Kuni Fudoki" contains a legend about Mt. Fuji (Mt. Fuji) and Mt. Tsukuba (the Fuji-Tsukuba legend). Mt. Fuji also features in many "mountain height comparison legends" that are widely distributed around the country. For example, it is said that Mt. Ashitaka (Mt. Ashitaka) in Suruga Province (Shizuoka Prefecture) came from China long ago to compare heights with Mt. Fuji, but the god of Mt. Ashigara called it insolent and kicked it down, causing it to become lower. Also, long ago, Yatsugatake and Mt. Fuji were competing to be the tallest, but they couldn't decide, so a gutter was put between the peaks of both mountains to let water flow, but the water flowed over Fuji, and Fuji lost. It is said that Fuji became angry and hit Yatsugatake on the head with the gutter and kicked it up, lowering it and giving it an uneven summit. Since the Kamakura period, this has been particularly common in travelogues, waka, and haiku, and in painting, Katsushika Hokusai's Thirty-six Views of Mount Fuji from the Edo period is famous.

It is believed that the practice of seeing Mount Fuji and worshipping it as an object of faith dates back to primitive beliefs, but it only took concrete form when it was linked to mountain Buddhism. It is said that the first worship of Mount Fuji was started by En no Ozunu, who established Shugendo, but it is unclear whether this is true. Worship of Fuji became popular after the Middle Ages, and worshipping was popularized by Hasegawa Kakugyo, the founder of the Fuji-ko sect. Fuji-ko monks were active throughout a wide area of eastern Japan, and established remote worship sites in various places by establishing branch shrines of Fuji Sengenjinja. Members of the sect would make the pilgrimage to Fuji for 20 days from the opening of the mountain on June 1st of the lunar calendar. During the Edo period, temple lodgings and stone chambers were also established, and the closing day of the mountain was July 27th. Climbers climb through the night, worship at the sunrise, and walk around the crater's rim.

In areas where Mount Fuji is visible, the weather is predicted by the amount of cloud cover. Volcanic caves around Mount Fuji are called Fuji Wind Cave, and taking advantage of the constant low temperatures there, they were used to store ice and inhibit the hatching of silkworm seeds.

[Shoji Inoguchi]

World Heritage Registration

In 2013, 25 constituent assets, including the Mt. Fuji area, surrounding shrines, the Fuji Five Lakes, Oshino Hakkai, Miho no Matsubara, etc., were registered as a World Heritage Site by UNESCO (United Nations Educational, Scientific and Cultural Organization) as "Mount Fuji - a place of worship and a source of artistic inspiration" (World Cultural Heritage). The constituent assets are as follows:

(1) Mount Fuji region (reading: Fujisan-iki) (cities, towns, and villages): Yamanashi Prefecture and Shizuoka Prefecture

(1-1) Mountaintop religious sites (reading: Sancho no Shinko Iseikigun) (location: Yamanashi Prefecture, Shizuoka Prefecture)

(1-2) Omiya-Murayama Trail (now Fujinomiya Trail)
[Reading] Omiya Murayamaguchi and Zando (Genfuji no Miyaguchi and Zando)
[Location] Fujinomiya City, Shizuoka Prefecture

(1-3) Suyama Ascending Route (currently Gotemba Ascending Route)
[Reading] Suyamaguchi to Zandou (Gengotenbaguchi to Zandou)
[Location] Gotemba City, Shizuoka Prefecture

(1-4) Subashiriguchi Mountain Trail [Reading] Subashiriguchi and Zando [City and Town] Oyama Town, Shizuoka Prefecture

(1-5) Yoshidaguchi Mountain Trail [Reading] Yoshidaguchi and Zando [City and Town] Fujiyoshida City, Yamanashi Prefecture, Fujikawaguchiko Town

(1-6) Kitaguchi Motomiya Fuji Sengen Shrine [Reading] Kitaguchi Hongu Fuji Sengen Jinja [Location city, town, village] Fujiyoshida city, Yamanashi prefecture

(1-7) Nishiko [Reading] Saiko [City and Town] Fujikawaguchiko Town, Yamanashi Prefecture

(1-8) Lake Shoji [Reading] Shojiko [City and Town] Fujikawaguchiko Town, Yamanashi Prefecture

(1-9) Lake Motosu [Reading] Motosuko [City and Town] Minobu Town, Fujikawaguchiko Town, Yamanashi Prefecture

(2) Fujisan Hongusen Gentaisha (Reading) Fujisan Hongusen Gentaisha (located in city, town, village) Fujinomiya City, Shizuoka Prefecture

(3) Yamamiya Sengen Jinja (Reading) Yamamiya Sengen Jinja (Location City, Town, and Village) Fujinomiya City, Shizuoka Prefecture

(4) Murayama Sengen Shrine [Reading] Muraya Nai Genjinja [Location City, Town, and Village] Fujinomiya City, Shizuoka Prefecture

(5) Suyama Sengen Shrine [Reading] Suyana Genjinja [Location City, Town, and Village] Susono City, Shizuoka Prefecture

(6) Fuji Asama Shrine (Subari Asama Shrine)
[Reading] Fujisengen Jinja (Subashirisengen Jinja)
[Location city/town] Oyama Town, Shizuoka Prefecture

(7) Kawaguchi Asama Shrine [Reading] Kawaguchi Asama Jinja [Location] Fujikawaguchiko Town, Yamanashi Prefecture

(8) Fuji Omuro Sengen Shrine [Reading] Fuji Omuro Sengen Jinja [Location City, Town, and Village] Fujikawaguchiko Town, Yamanashi Prefecture

(9) Missionary housing (formerly Togawa family housing)
[Reading] Oshikaku (Kyuuga Kaku)
[Location city, town, village] Fujiyoshida city, Yamanashi prefecture

(10) Master's housing (Osano family housing)
[Reading] Osanoke Carpet
[Location city, town, village] Fujiyoshida city, Yamanashi prefecture

(11) Yamanakako [Reading] Yamanakako [Location] Yamanakako [City and Town] Yamanakako Village, Yamanashi Prefecture

(12) Lake Kawaguchiko [Reading] Kawaguchiko [Location] Fujikawaguchiko Town, Yamanashi Prefecture

(13) Oshino Hakkai (Deguchi Pond)
[Reading] Oshinohai (deguchike)
[Location city/town] Oshino Village, Yamanashi Prefecture

(14) Oshino Hakkai (Okamaike)
[Reading] Oshinohai (Okamaike)
[Location city/town] Oshino Village, Yamanashi Prefecture

(15) Oshino Hakkai (Bottom Pond)
[Reading] Oshino-no-ha (please go through there)
[Location city/town] Oshino Village, Yamanashi Prefecture

(16) Oshino Hakkai (Choshi Pond)
[Reading] Oshinohai (Choshike)
[Location city/town] Oshino Village, Yamanashi Prefecture

(17) Oshino Hakkai (Yuike)
[Reading] Oshino-no-haku (waku-ke)
[Location city/town] Oshino Village, Yamanashi Prefecture

(18) Oshino Hakkai (Drug Pond)
[Reading] Oshinohai (gourashi)
[Location city/town] Oshino Village, Yamanashi Prefecture

(19) Oshino Hakkai (Kagami Pond)
[Reading] Oshinohai (Kagamike)
[Location city/town] Oshino Village, Yamanashi Prefecture

(20) Oshino Hakkai (Iris Pond)
[Reading] Oshinohai (Shobuike)
[Location city/town] Oshino Village, Yamanashi Prefecture

(21) Funatsu Tiger Tree Type [Reading] Funatsu Tainai Jukei [Location City, Town, and Village] Fujikawaguchiko Town, Yamanashi Prefecture

(22) Yoshida Tinai Tree Type [Reading] Yoshida Tainai Jukei [Location City, Town, and Village] Fujiyoshida City, Yamanashi Prefecture

(23) Hitoana Fujiko Ruins [Reading] Hitoana Fujiko Iseki [Location] Fujinomiya City, Shizuoka Prefecture

(24) Shiraito no Taki [Reading] Shiraito no Taki [City and Town] Fujinomiya City, Shizuoka Prefecture

(25) Miho Matsubara [Reading] Miho Matsubara [Location] Shizuoka City, Shizuoka Prefecture

[Editorial Department]

になったんです。 English: The first thing you can do is to find the best one to do . "The Plants of Mt. Fuji" by Watanabe Kenji (1993, Shizuoka Shimbun)" ▽ "Mt. Fuji and the Japanese" edited by Seiyusha Editorial Department (2002, Seiyusha)" ▽ "The Story of Mt. Fuji Weather Station by Shizaki Daisaku (2002, Seisendo Shoten)" ▽ "Hirano Eiji Collection of Works: Fuji Faith and Fuji Koto (2004, Iwata Shoin)" ▽ "Fuji Volcano Editorial Committee (Revised Edition)" (2011, Japan Society of Volcanic Studies)" ▽ "Mt. Fuji Fuji" by Morishita Akira (Kodansha Gendai Shinsho)" ▽ "Mt. Fuji" by Nagahara Keiji, "The Great Explosion of Mt. Fuji" (Shueisha Shinsho)"

Mount Fuji
Boasting the highest elevation in Japan (3,776m) and a beautiful mountain shape, this sacred mountain is a symbol of Japan. It has been worshipped as an object of faith since ancient times. It shows different appearances depending on the season and the direction from which it is viewed. It is the center of Fuji-Hakone-Izu National Park. The photo was taken from the sky on the Shizuoka side. Part of the World Cultural Heritage "Mount Fuji - Object of Faith and Source of Artistic Inspiration" (registered in 2013) Fujinomiya City, Fuji City, Susono City, Gotemba City, Oyama Town, Sunto District, Shizuoka Prefecture / Fujiyoshida City, Narusawa Village, Minamitsuru District, Yamanashi Prefecture ©Shogakukan ">

Mount Fuji

Geological cross-section of Mt. Fuji
©Shogakukan ">

Geological cross-section of Mt. Fuji

Hoei Crater
An explosive crater in the southeastern part of the summit of Mt. Fuji. The photo is on the right side of the side volcano Hoeisan © Susono City Tourism Association ">

Hoei Crater

Mihomatsubara and Mt. Fuji
Mt. Fuji view from Miho Coast © Shizuoka Prefecture Tourism Association ">

Mihomatsubara and Mt. Fuji

Red Fuji
Mount Fuji is dyed red in the mornings from late summer to early autumn. Photo shows a view from the shore of Lake Yamanaka © Yamanashi Tourism Promotion Organization ">

Red Fuji

Diamond Fuji
The phenomenon of the sun overlapping on the summit of Mt. Fuji. The view of this image reflected on the surface of the lake is called Double Diamond Fuji. Photographed by Lake Motosu © Yamanashi Tourism Promotion Organization ">

Diamond Fuji

Mount Fuji and tea fields
View from Fuji City, Shizuoka Prefecture © Shizuoka Prefecture Tourism Association ">

Mount Fuji and tea fields

Opening of Mt. Fuji
The day before the Mt. Fuji opening festival on July 1st, the "Odowari opening" ceremony will be held at Kitaguchi Motomiya Fuji Sengen Shrine © Yamanashi Tourism Promotion Organization ">

Opening of Mt. Fuji

『名勝八景冨士暮雪』
Utagawa Toyokuni (Second-generation) Painting National Diet Library ">

『名勝八景冨士暮雪』

"Thirty-six Fuji Views: Suruga Miho no Matsubara"
Paintings of Utagawa Hiroshige, 1858 (Ansei 5) of the National Diet Library ">

"Thirty-six Fuji Views: Suruga Miho no Matsubara"

Oshino Hakkai
Eight springs thought to have their source in the groundwater of Mt. Fuji. They have been revered as divine springs since ancient times. The photo shows Wakuike Pond, which has the largest amount of spring water among the eight seas. Nationally designated natural monument Part of the World Cultural Heritage "Mt. Fuji - a place of worship and a source of artistic inspiration" (registered in 2013) Oshino Village, Minamitsuru District, Yamanashi Prefecture ©Yamanashi Tourism Organization ">

Oshino Hakkai

Aokigahara
A primitive forest spreading at the northwest foot of Mt. Fuji. Also known as the Aokigahara Sea of Trees. Approximately 30km. It is one of Japan's most representative sea of trees and is known for its unique vegetation patterns. Part of Fuji Hakone Izu National Park. Nationally designated natural monument Fujikawaguchiko-cho, Minamitsuru-gun, Yamanashi Prefecture © Yamanashi Tourism Promotion Organization ">

Aokigahara

Map of the constituent assets of "Mt Fuji: Objects of Faith and Source of Art" World Cultural Heritage Site
©Shogakukan Illustration/Shogakukan Creative ">

World Cultural Heritage Site "Mt. Fuji: Objects of Faith and Art...

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

山梨・静岡両県にまたがる、玄武岩を主とする成層・円錐火山(えんすいかざん)。かつての富士火山帯の主峰であるが、全国最高の標高（3776メートル）と美しい容姿のために、古来、日本の象徴として仰がれ、親しまれ、海外にもよく知られる活火山。その傾斜は山頂部で32～35度、裾野(すその)は2～3度で、美しい対数曲線を描き、基底の直径は東西約35キロメートル、南北約38キロメートル。

　昔は「不尽」「不二」「富慈」などと書かれ、アイヌ語の「フチ」（火）に由来するとの説もある。富士箱根伊豆国立公園（1936年指定）の主人公で、長崎県の雲仙(うんぜん)岳とともに特別名勝の指定を受けている。裾を広く四方に広げているが、北麓(ほくろく)には、御坂(みさか)山地などの周囲の山々との間に、富士山の溶岩流でせき止められて生じた富士五湖（山中、河口(かわぐち)、西(さい)、精進(しょうじ)、本栖(もとす)）があり、観光開発が進み、四季を通じて来遊者がとくに多い。日本三名山の一つ（他は立山(たてやま)と白山(はくさん)）。

［諏訪　彰・中田節也］

成り立ち・生い立ち

富士山は日本の最高峰であるが、実はその下に数十万年前までにできた先小御岳(せんこみたけ)、小御岳の古い火山が存在する。富士山自身は古富士と新富士の二つの火山からできており、新富士火山は約1万年前から活動を開始した。噴出物の厚さは最大1500メートル足らずである。つまり、私たちが仰ぎ見る富士山は、何重にも火山が重なった結果できた成層火山である。また、富士山は比較的若い火山で、過去約300年も噴火しなかったとはいえ、将来かならず再噴火すると考えられ、油断は禁物である。

　富士山は、フィリピン海プレートが日本列島に衝突している伊豆半島の付け根の背後という特異な場所に位置している。約2500万～2000万年前（中新世）の海底火山噴出物からなる地層（御坂統(みさかとう)）が小御岳や同時代の愛鷹火山(あしたかかざん)の基盤である。小御岳火山の一部は、河口湖からの登山自動車道「富士スバルライン」の終点、小御岳（五合目）付近に露頭している。古富士火山はいまから約8万年前に活動を始め、激しい爆発型噴火を繰り返し、南関東にも盛んに玄武岩質の火山灰を降らせ、京浜地域の台地面をつくっている「関東ローム」（詳しくは立川ローム(たちかわろーむ)、武蔵野ローム(むさしのろーむ)）を堆積(たいせき)させた。その火山灰は、東京付近では、肉眼では個々の粒を識別しかねるほど細かく、層厚も数メートルであるが、それを富士山方向にたどっていくと、しだいに粒が粗くなり、層厚も増していく。東麓の御殿場(ごてんば)、須走(すばしり)などでは、褐色で粗粒の火山礫(れき)の地層が重なって数十メートルの厚い層をなしている。

　また、富士山麓では、数万年前におきた山体崩壊の堆積物（岩屑なだれ堆積物(がんせつなだれたいせきぶつ)）がみいだされる。これは「古富士泥流」とよばれ、古富士火山の表層をなしている。この古富士火山は、いまから約1万年前、つまり更新世から現世に移るころ、噴火活動の様相が急変した。以後、約1000年にわたり、おもに多量の溶岩を四方へ流出させる噴火活動が盛んに繰り返され、現在見られる富士山の原形がほぼできあがった。中央火口から30～40キロメートルの遠方まで流下した猿橋溶岩(さるはしようがん)、岩淵溶岩(いわぶちようがん)、三島溶岩(みしまようがん)などがそれである。古富士山の一部が、1707年（宝永4）の大噴火で生じた火口に「赤岩(あかいわ)」（標高約2700メートル）としてわずかに露出している。

　いまから約1万年前から新富士火山が活動を開始した。新富士火山は、近くは前記の宝永(ほうえい)大噴火まで、しばしば噴火を繰り返し、爆発による火山砕屑(さいせつ)物や流出した溶岩で古富士火山を覆い隠しながら成長してきたが、約2500年前に東斜面で山体崩壊がおき「御殿場泥流」を堆積した。富士山は頂部から山腹には寄生火山・寄生火口が60以上あり、多くが山頂を通る北北西―南南東方向（富士火山帯の走向）に分布する。また、山麓に分布する風穴(ふうけつ)・氷穴(ひょうけつ)は玄武岩溶岩が流れる際にできた溶岩トンネルの一部である。富士五湖は、玄武岩質溶岩が河川をせき止めてできたものである。その湖底からは富士山の地下水も湧(わ)き出しているが、山中湖以外は自然の排水口がなく、水位はかなり激しく変動する。なお、皇室系譜で第7代の孝霊(こうれい)天皇5年に、一夜のうちに大陥没により琵琶(びわ)湖ができ、同時に、大隆起で富士山が誕生したなどという、富士山の出現時期についての諸伝説があるが、科学的には不合理で、事実に反する。

［諏訪　彰・中田節也］

有史時代の噴火活動

新富士火山の噴火活動は、平安時代（およそ8世紀末～12世紀末）まではとくに活発に繰り返された。最古の噴火記録は、万葉歌人の高橋虫麻呂(たかはしのむしまろ)の作と伝えられる長歌「不尽山(ふじさん)を詠む歌」のなかの「燃ゆる火を雪もて消(け)ち　降る雪を火もて消ちつつ」と書かれた部分で、養老(ようろう)年間（717～724）の西暦720年前後の噴火であろうと推察されている。歴史書に残された噴火は、『続日本紀(しょくにほんぎ)』に記された781年（天応1）を皮切りに、800年（延暦19）、864年（貞観6）、1707年（宝永4）の三大噴火など、計10回ほどである。

　1083年（永保3）までは、平均して約30年ごとに噴火を繰り返したが、それから1707年の大噴火までの6世紀余の間にはわずか3回しか噴火せず、ことに1083年の噴火の後は約300年間も噴火がみられなかった。さらに、1707年の大噴火の後も、すでに約300年が流れ去った。しかも、1083年までの諸噴火は概して勢いが盛んで、しばしば溶岩流も発生したが、その後は火山灰を放出する噴火に限られ、また、噴火規模の点でも、1707年を除けば、さしたる噴火はなかった。また、『本朝文粋(ほんちょうもんずい)』中の都良香(みやこのよしか)の「富士山記」、作者不明の『竹取物語』など、多くの文献からみて、富士山は有史時代に入ってからも永く煙を吐き続けていたと考えられる。その噴煙活動が画期的に衰え始めたのは、前記の1083年の噴火の後である。それでも、以後約1世紀間は連続的に多少とも噴煙していたことが、西行(さいぎょう)法師の『山家集(さんかしゅう)』などからうかがえるが、阿仏尼(あぶつに)の『十六夜(いざよい)日記』などからみて、平安・鎌倉両時代の交(こう)に噴煙はまったくとだえてしまったらしい。

　『日本後紀』『日本紀略』などによれば、800年の大噴火では、山頂や山腹で爆発活動と溶岩流出活動が盛んに展開され、広く東海道および南関東地方の交通文化のうえにも一大変化をもたらした。東海道の足柄路(あしがらじ)が多量の降灰砂でふさがれたため、802年に箱根路が新しく開かれた。足柄路も803年に再開されたが、東名高速道路ができるまで、箱根路にお株を奪われてきた。また、北東麓にあった宇津湖はこの大噴火の溶岩流鷹丸尾(たかまるび)によって分断され、一方の山中湖は残っているが、忍野(おしの)地域の湖では湖水が桂(かつら)川となって流出し、「忍野八海(はっかい)」（国指定天然記念物）を残して干上がった。864～866年の山腹噴火のようすは『三代実録』などに記されているが、地質調査からもその活動の激しさが推察され、富士山の有史以来最大の噴火で、青木ヶ原、剣丸尾(けんまるび)などの大溶岩流が発生し、前者は北麓の剗海(せのうみ)を西(さい)湖と精進(しょうじ)湖に二分した。ボーリング調査によると、このときの噴出物量は宝永噴火のそれを上回っていたようである。

　1707年の大噴火は、山腹での激しい爆発活動に終始し、まず、富士山としては約2500年ぶりのデイサイト質の火山灰・軽石や黒曜石が噴出し、引き続いて玄武岩質の火山灰・火山砕屑物が噴出した。総噴出物量は約17億立方メートル（マグマに換算すると6億8000万立方メートル）で、東方約90キロメートルの川崎でも約5センチメートルの厚さの火山灰が積もった。当時の状況は、新井白石(あらいはくせき)の『折たく柴(しば)の記』などに記されている。江戸でも噴火の強い地震、鳴動、爆発音、空振がしきりに感じられ、黒雲が天を覆い、噴火開始の数時間後から灰白色の灰に引き続いて、灰黒色の灰が降り、昼間も灯火を用いたという。江戸では降灰が10日以上続き、降ってくる火山灰と堆積(たいせき)した火山灰が風で巻き上げられたため、関東一円に呼吸器疾患が大流行したという。宝永噴火の49日前にはマグニチュード8.7の地震（宝永東海地震）がおきていた。

［諏訪　彰・中田節也］

火山の現状と将来

富士山の頂には直径約800メートル、周囲約3.5キロメートル、深さ200余メートルの火口があり、「内院」とよばれている。その火口縁は「お鉢」とよばれ、南西側に全国最高点・標高3776メートルの剣ヶ峰(けんがみね)、北側には標高3756メートルの白山(はくさん)岳があり、剣ヶ峰から東回りに三島岳、駒(こま)ヶ岳、成就(じょうじゅ)岳、大日(だいにち)岳、久須志(くすし)（薬師）岳、白山岳と、数珠(じゅず)つなぎに火口を取り囲んでいる。「お鉢巡り」は約4キロメートルで、1時間半近くかかる。

　剣ヶ峰には、1936年（昭和11）創設の富士山測候所があり、日本の気象観測の重要拠点で、最大探知距離800キロメートルのレーダーがあった。衛星による観測が充実したため、富士山測候所の常駐観測は2004年（平成16）10月より廃止され、2008年に富士山特別地域気象観測所（無人）となった。気温は年平均零下6.5℃、従来の最低は零下38.0℃、最高は17.8℃で、夏でも雪が降ることがある。従来の最大風速は秒速72.5メートルであり、冬には連日秒速20メートル以上の強風下で吹雪(ふぶき)が続くことが多い。酸素量や気圧は平地の約3分の2で、水は88～87℃ほどで沸騰する。富士山全体への降水量は年間約20億立方メートル（約2割は積雪による）と見積もられるが、山腹には湧水がごく乏しい。新富士火山を構成する溶岩流や火山砕屑物の層が多孔質で、水が地下深く浸透してしまうためである。この伏流水は、古富士火山の表層をなす不透水性の泥流堆積物の上面に沿って流下し、山麓の白糸ノ滝、富士五湖底、忍野八海などに湧出するほか、御殿場、三島、富士宮(ふじのみや)各市などでの豊富な湧水は地域産業の発展に役だっている。山腹での地下水の取得は、富士山の本格的開発への鍵(かぎ)である。もっとも、山麓をはじめ、中腹（北側の五合目、南側の新五合目など）まで自動車道路網が整備され、観光開発が飛躍的に進展し、むしろ、自然保護や防災との兼ね合いが深刻な難問になってきた。また、裾野には自衛隊やアメリカ軍の演習地がある。

　富士火山は、全国民の関心の的であるだけに、第二次世界大戦後も、噴煙の発生や地温の上昇、噴気の活発化などの異常現象の発現がしばしば報じられたが、実は、強風やつむじ風で砂塵(さじん)が吹き上げられて噴煙に見間違えられたり、積雪が強風や雪崩(なだれ)で吹き飛ばされて局所的に地肌が露出したのを、地温の上昇や噴気の活発化のためと早合点されたものばかりであった。山頂の成就岳の荒牧(あらまき)、山腹の宝永火口や須走口三合目などに散在する噴気・地熱部の温度も、近年はかなり低下しており、火山性地震はときどき観測されている。

　2002年（平成14）秋ごろから山頂北東部の地下約15キロメートルの深さを震源とする低周波地震が群発し、防災対策がとられ始めた。国や地方自治体も富士山のハザードマップを作成し、防災訓練を実施するようになった。2011年3月11日のマグニチュード9.0の東北地方太平洋沖地震の直後、3月15日に富士山の直下約10キロメートルの深さを震源とするマグニチュード6.4の地震が発生した。その後1年間は、地震活動が弱まりながら継続したが、地震活動以外に噴火の前兆となる現象は観測されなかった。富士山では、防災科学技術研究所、国土地理院、気象庁、東京大学、山梨県などが地震計やGPS（全地球測位システム）などによる観測を続けている。また、この付近には、東海大地震に備えての関係諸機関の各種の観測網も張り巡らされている。さらに、産業技術総合研究所、東京大学、日本大学などでは、富士山の過去の噴火履歴を解読するための研究を精力的に進めている。

［諏訪　彰・中田節也］

山体の崩壊

富士山のもっとも深刻な問題は、風化・侵食による斜面崩壊である。標高2450メートル以上は露岩地帯で、風化作用が進み、また山腹には、西側の「大沢」、北東側の「吉田大沢」など、多数の沢（放射谷）が発達している。とくに前者の「大沢崩れ」は長さ約10キロメートル、幅最大500メートル、深さ約150メートルの巨大な谷で、裾野から剣ヶ峰に達する。斜面崩壊は続いている。吉田大沢では、1980年（昭和55）夏、吉田口登山道「砂走り」を下山中の数百人の集団が落石群に襲われ、死者12人、負傷者31人を出した。斜面崩壊は東側山腹でも急速に広がっている。この問題に対して、防災工事も行われているが、抜本的対策はなく、まさに不治（富士）の病である。

　また、富士山頂には、南側の剣ヶ峰と北側の白山岳に三角点があり、前者が日本の最高峰であるが、その標高は、明治維新後の1885年（明治18）に3778メートルと正式に測量されてからも、測量し直すたびに低下してきた。1926年（大正15）の測量で、現在広く知られている3776(みななむ)メートルの根拠である3776.29メートルが得られた。その後、山頂の岩石が崩れて三角点標石が危険になったので、第二次世界大戦後の1962年（昭和37）に標石を下げて埋め直し、標高は3775.63メートルとなった。四捨五入すれば前と同じで、地図帳を直さなくてすんだが、実は、そうなるように細工して、コンクリートで固めたのである。さらに1977年にも同様な作業を行い、標高3776メートルを維持させているという。国土地理院も、実に苦心惨憺(さんたん)しているようである。

［諏訪　彰］

植生

植物相からみると、富士山はこの地域に固有に分化したハコネコメツツジ属、ハコネラン属、アマギカンアオイ、カナウツギ、フジザクラなどの分類群を有しており、中部日本の山岳地域のなかでも特徴的である。したがって、日本の植物区系区分のなかでは箱根、伊豆諸島などとともにフォッサマグナ地域に含められている。また、火山砂礫(されき)地にはイワオウギ、ムラサキモメンヅルなど遺存分布と考えられる要素もみられる。しかし、一方では周辺の高山に分布するハイマツがみられないなど、その植物相の形成については、まだ未解明の部分を多く残している。

　植生の面からみると、とくにその南麓(なんろく)は、海岸から3776メートルの山頂まで日本でもっとも大きな高度傾度を有しており、垂直分布帯が発達している。海岸から標高800メートル付近までは暖温帯（高度帯では丘陵帯）の常緑広葉樹林の領域で、400メートル以下にはタブノキ林、スダジイ林などが分布し、その上部はアカガシ林に移行する。しかし、この範囲は人為的破壊によって自然植生は断片的にしかみられず、そのほとんどは、居住地、スギ・ヒノキなどの植林地、自衛隊の演習地や放牧地としてのススキ草原となっている。

　800～1600メートルにかけては冷温帯（山地帯）の落葉広葉樹林の領域である。この冷温帯と暖温帯の移行部に相当する800～1000メートルの地域には、丸尾(まるび)とよばれる溶岩流がいくつか分布する。この溶岩流はいずれも1000～1500年前に噴出したもので、現在ではツガ、ヒノキ、アカマツなどの針葉樹が優占した森林が発達している。樹海で知られる青木ヶ原丸尾はそのうちでも最大級で、東西8キロメートル、南北6キロメートルに及ぶツガとヒノキを主とする森林となっている。また、忍野の鷹丸尾(おしののたかまるび)はハリモミ林が発達する特異なものである。この両者はそれぞれ「富士山原始林」「忍野八海(はっかい)」として国の天然記念物に指定されている。これ以外の土壌がよく発達した地域ではブナが優占し、一部ウラジロモミを交えた落葉広葉樹林がみられる。

　1600メートル以上は亜高山帯（亜寒帯、寒温帯）の常緑針葉樹林である。富士山の場合、亜高山帯の下部はコメツガ、上部はシラビソが優占する（とくに上部ではカラマツ、ダケカンバを多く交え、一部にオオシラビソが混じる）。ほぼ2500メートルが森林限界で、ダケカンバ、ミヤマハンノキ、ミネヤナギなどがしだいに樹高を減じて限界を縁どっている。御庭(おにわ)周辺、宝永(ほうえい)火口などではカラマツが匍匐(ほふく)状になって森林限界の上部に出現する。さらにその上部はイタドリ、オンタデ、フジハタザオなどが散生した高山帯の火山荒原植生となる。

　東斜面の御殿場から須走(すばしり)付近は、1707年（宝永4）の火口（宝永火口）の噴火によって植生が破壊されたうえ、その後の基質がスコリア質（岩滓(がんさい)質）で不安定なため、1300メートル以上の地域は遷移の進行が遅く、いまだにイタドリ、オンタデなどが散生した火山荒原植生が広がり、特異な高山帯的景観を呈している。一方、この裸地には、ミヤマハンノキ、ミネヤナギ、ダケカンバなど亜高山帯上部の植生を構成する種が降下してきているため、この裸地から安定な斜面に発達する森林に向かって、遷移の各段階を構成する群落が帯状に配列している。このように富士山には、植生遷移の進行速度の差によって発達段階の異なる植物垂直分布帯や植生のモザイク構造がよく認められる。

［大澤雅彦］

動物相

富士山の動物相は、日本の温帯系要素にオコジョ、トガリネズミ、ホシガラスなど若干の寒帯系要素が加わった本州中部山地の典型的なものである。富士山東面の須走付近は東日本有数の鳥類の繁殖地で「探鳥会」発祥の地として知られる。ここの山麓帯ではヤマドリ、ヨタカ、クロツグミ、ウグイス、キバシリ、亜高山帯ではホシガラス、アオバト、マミジロ、ヤマドリ、コマドリなどが繁殖し、樹木限界付近ではカヤクグリ、イワヒバリがみられる。鳥類が豊富なことは、青木ヶ原から精進(しょうじ)口登山道を経て吉田口登山道五合目に達する森林地帯でも同様であるが、この幅の狭い老年期の森林は日本有数の森林生コウモリの宝庫である。ここでは洞窟(どうくつ)生のコキクガシラコウモリ、キクガシラコウモリ、ウサギコウモリなどのほか、樹洞生のフジホオヒゲコウモリ、カグヤコウモリ、クビワコウモリ、コテングコウモリがみられ、尾瀬固有と思われていたオゼホオヒゲコウモリも生息していることが確認された。

　この地帯にはほかの動物も種類が豊富で、亜高山帯にはカモシカ、オコジョ、ヒメヒミズ、トガリネズミ、リス、モモンガ、ヤマネ、低山帯上部にはフジミズラモグラ、カゲネズミ、ヒミズ、ヒメネズミ、ジムグリ、シロマダラ、ヒキガエル、フジミドリシジミなどがみられるほか、ムササビ、ツキノワグマも姿をみせる。山麓の草原地帯にはコウベモグラ、ハタネズミ、カヤネズミ、ノウサギ、イノシシ、ノビタキ、セッカ、ヒメシロチョウ、ヤマキチョウなどが多く、水場がある大宮口の森林にはシカがみられる。標高2500メートル以上の地帯は高山地帯に相当するが、ここまで低地ないし低山生のハタネズミ、アカネズミ、ヒメネズミ、ヤマネが進出しており、登山シーズン以外にはイノシシ、カモシカ、ツキノワグマ、キツネ、テンなどが山頂まで姿をみせる。

　しかし、本州の高山動物とみられるニイガタヤチネズミ、アズミトガリネズミ、ライチョウ（1960年に7羽放されたが姿を消した）、高山チョウのタカネヒカゲ、タカネキマダラセセリ、コヒオドシ、クモマツマキチョウなどは富士山には生息しない。また、本州日本海側および中部以北に分布するシナノミズラモグラ、トウホクノウサギ、西日本系のスミスネズミ、北日本系のトウホクヤチネズミなどもみられない。愛鷹山には富士山本体にいないサル、暖帯系のキリシマミドリシジミが生息する。富士山には、フジミドリシジミ、フジキオビなど富士の名をもつ動物が多いが、ニホンウサギコウモリ、オオタカの亜種など学名が富士にちなんだものも少なくない。しかし、この山に固有の種は知られていない。

［今泉吉典］

登山

富士山に初めて登ったのは聖徳太子あるいは役小角(えんのおづぬ)とする説もあり、9世紀ごろはすでに盛んに登られていたと考えられるがさだかではない。1149年（久安5）に駿河(するが)国（静岡県）の末代上人(まつだいしょうにん)が山頂に仏閣を建てた記事があり、村山口から登山が行われたという。近世初期に長谷川角行(はせがわかくぎょう)（1541―1646）によって富士講が開かれ、先達(せんだつ)によって引率され、白装束に身を固めた人々が「六根清浄」と唱えながら登山した。山麓(さんろく)の富士吉田は浅間神社(せんげんじんじゃ)の門前町であり、日本第一の信仰登山地として発達し、登山者の集合地となった。登山口は富士宮口を正面とし、吉田口、御殿場(ごてんば)口、須走(すばしり)口が多く用いられ、村山口、須山口はその後廃道化した。女性は不浄とされ、吉田口では二合目の小浅間上の御釜(おかま)まで、村山口では一合目の女人堂までしか登れなかったが、1866年（慶応2）イギリス公使パークス夫人が女性として初めて登山した。

　開山期間は7月1日から8月26日の火祭までであったが、近年は8月31日まで開かれ、各登山口の山小屋も開かれている。多いときはこの期間に100万人近くの登山者があるが、1964年（昭和39）河口湖からスバルラインの有料自動車道が吉田口五合目まで開かれ、1970年に御殿場口の五合目まで表富士周遊道路がつくられてからは、山麓から五合目までの登山道はさびれてしまった。山頂の火口を一周するお鉢めぐりや、五合目を一周するお中道回りも行われた。1871年（明治4）イギリスのベイヤード中尉が積雪期に初めて登山し、また1895年には日本における高山気象観測の開拓者である野中至(いたる)が気象観測のため厳冬期に登山した。富士山は独立の高峰であるため、冬期は蒼氷(そうひょう)が発達し、氷雪登山の舞台となり、アルピニストが多く訪れるようになった。しかし、日本第一の高峰であるため、めまい、頭痛など高山病の症状をおこす人も多く、また冬期は突風や雪崩(なだれ)による遭難事故も多発しているので注意を要する。

［徳久球雄］

民俗・信仰

富士山の秀麗な姿は、『万葉集』『竹取物語』をはじめ数々の文芸や紀行文に取り入れられているほか絵画にも描かれている。『常陸国風土記(ひたちのくにふどき)』には福慈山(ふじさん)（富士山）と筑波山(つくばさん)に関する伝説（富士筑波伝説）がみえる。また各地に広く分布する「山の背くらべ伝説」には富士山が多く登場する。たとえば駿河(するが)国（静岡県）の足高山(あしたかやま)（愛鷹(あしたか)山）は、大昔、唐土(もろこし)（中国）から富士山と背くらべをするためにきたが、足柄山(あしがらやま)の明神が、生意気だといって足で蹴(け)くずしたので低くなったという。また八ヶ岳(やつがたけ)と富士山とが、大昔、背の高さを競って決着がつかず、双方の頂上へ樋(ひ)を渡して水を流すと、水は富士のほうへ流れて富士が負けた。富士は怒って、その樋で八ヶ岳の頭をなぐって蹴上げたので低くなり、でこぼこの頂上になったという。鎌倉時代以降はとくに紀行・和歌・俳句に多く、絵画では江戸時代の葛飾北斎(かつしかほくさい)の『冨嶽三十六景(ふがくさんじゅうろっけい)』が名高い。

　富士山を霊視し、また信仰の対象として崇(あが)めることは、原始信仰以来のものと想像されるが、山岳仏教と結び付いて初めて具体的な形を整えてきた。富士山への登拝の始まりは、修験道(しゅげんどう)を開いた役小角(えんのおづぬ)であると伝えられているが、事実かどうか明らかではない。富士の信仰が盛んになったのは中世以後のことであり、登拝することは富士講の開祖である長谷川角行によって広められた。富士講の行者(ぎょうじゃ)は東日本の広い範囲に活躍し、各地に富士浅間神社(ふじせんげんじんじゃ)を分祀(ぶんし)して遙拝(ようはい)所を設けた。講中の者は、旧暦6月1日の山開きから20日間、富士詣で(ふじもうで)と称して登拝した。江戸時代には宿坊(しゅくぼう)や石室(いしむろ)も整い、7月27日を山じまいとした。登拝者は夜を徹して登り、御来迎(ごらいごう)（日の出）を拝み、火口を巡る「お鉢巡り」などをする。

　富士山の見える地域では、雲のかかりぐあいで天候を予測する。また富士山周辺の火山性洞窟(どうくつ)を富士風穴(ふうけつ)といい、気温が低く一定なことを利用して、氷の保存や蚕の種の孵化(ふか)抑制などを行なっていた。

［井之口章次］

世界遺産の登録

2013年（平成25）には富士山域をはじめ周辺の神社、富士五湖、忍野八海(おしのはっかい)や三保松原(みほのまつばら)等を含めた25の構成資産が、ユネスコ（国連教育科学文化機関）により「富士山―信仰の対象と芸術の源泉」として世界遺産の文化遺産に登録された（世界文化遺産）。構成資産は以下のとおりである。

(1)富士山域
〔読み〕ふじさんいき
〔所在市町村〕山梨県・静岡県

　(1-1)山頂の信仰遺跡群
　〔読み〕さんちょうのしんこういせきぐん
　〔所在市町村〕山梨県・静岡県

　(1-2)大宮・村山口登山道（現富士宮口登山道）
　〔読み〕おおみや・むらやまぐちとざんどう（げんふじのみやぐちとざんどう）
　〔所在市町村〕静岡県富士宮市

　(1-3)須山口登山道（現御殿場口登山道）
　〔読み〕すやまぐちとざんどう（げんごてんばぐちとざんどう）
　〔所在市町村〕静岡県御殿場市

　(1-4)須走口登山道
　〔読み〕すばしりぐちとざんどう
　〔所在市町村〕静岡県小山町

　(1-5)吉田口登山道
　〔読み〕よしだぐちとざんどう
　〔所在市町村〕山梨県富士吉田市・富士河口湖町

　(1-6)北口本宮冨士浅間神社
　〔読み〕きたぐちほんぐうふじせんげんじんじゃ
　〔所在市町村〕山梨県富士吉田市

　(1-7)西湖
　〔読み〕さいこ
　〔所在市町村〕山梨県富士河口湖町

　(1-8)精進湖
　〔読み〕しょうじこ
　〔所在市町村〕山梨県富士河口湖町

　(1-9)本栖湖
　〔読み〕もとすこ
　〔所在市町村〕山梨県身延町・富士河口湖町

(2)富士山本宮浅間大社
〔読み〕ふじさんほんぐうせんげんたいしゃ
〔所在市町村〕静岡県富士宮市

(3)山宮浅間神社
〔読み〕やまみやせんげんじんじゃ
〔所在市町村〕静岡県富士宮市

(4)村山浅間神社
〔読み〕むらやませんげんじんじゃ
〔所在市町村〕静岡県富士宮市

(5)須山浅間神社
〔読み〕すやませんげんじんじゃ
〔所在市町村〕静岡県裾野市

(6)冨士浅間神社（須走浅間神社）
〔読み〕ふじせんげんじんじゃ（すばしりせんげんじんじゃ）
〔所在市町村〕静岡県小山町

(7)河口浅間神社
〔読み〕かわぐちあさまじんじゃ
〔所在市町村〕山梨県富士河口湖町

(8)冨士御室浅間神社
〔読み〕ふじおむろせんげんじんじゃ
〔所在市町村〕山梨県富士河口湖町

(9)御師住宅（旧外川家住宅）
〔読み〕おしじゅうたく（きゅうとがわけじゅうたく）
〔所在市町村〕山梨県富士吉田市

(10)御師住宅（小佐野家住宅）
〔読み〕おしじゅうたく（おさのけじゅうたく）
〔所在市町村〕山梨県富士吉田市

(11)山中湖
〔読み〕やまなかこ
〔所在市町村〕山梨県山中湖村

(12)河口湖
〔読み〕かわぐちこ
〔所在市町村〕山梨県富士河口湖町

(13)忍野八海（出口池）
〔読み〕おしのはっかい（でぐちいけ）
〔所在市町村〕山梨県忍野村

(14)忍野八海（お釜池）
〔読み〕おしのはっかい（おかまいけ）
〔所在市町村〕山梨県忍野村

(15)忍野八海（底抜池）
〔読み〕おしのはっかい（そこぬけいけ）
〔所在市町村〕山梨県忍野村

(16)忍野八海（銚子池）
〔読み〕おしのはっかい（ちょうしいけ）
〔所在市町村〕山梨県忍野村

(17)忍野八海（湧池）
〔読み〕おしのはっかい（わくいけ）
〔所在市町村〕山梨県忍野村

(18)忍野八海（濁池）
〔読み〕おしのはっかい（にごりいけ）
〔所在市町村〕山梨県忍野村

(19)忍野八海（鏡池）
〔読み〕おしのはっかい（かがみいけ）
〔所在市町村〕山梨県忍野村

(20)忍野八海（菖蒲池）
〔読み〕おしのはっかい（しょうぶいけ）
〔所在市町村〕山梨県忍野村

(21)船津胎内樹型
〔読み〕ふなつたいないじゅけい
〔所在市町村〕山梨県富士河口湖町

(22)吉田胎内樹型
〔読み〕よしだたいないじゅけい
〔所在市町村〕山梨県富士吉田市

(23)人穴富士講遺跡
〔読み〕ひとあなふじこういせき
〔所在市町村〕静岡県富士宮市

(24)白糸ノ滝
〔読み〕しらいとのたき
〔所在市町村〕静岡県富士宮市

(25)三保松原
〔読み〕みほのまつばら
〔所在市町村〕静岡県静岡市

［編集部］

『木澤綏他著『富士山　自然の謎を解く』（1969・NHKブックス）』▽『国立公園協会編『富士山総合学術調査報告書　富士山』全2冊（1971・富士急行株式会社・非売品）』▽『清水清著『富士山の植物』（1977・東海大学出版会）』▽『井上浩著『自然観察シリーズ・富士山の植物』（1982・小学館）』▽『諏訪彰監修『富士山大雑学』（1983・廣済堂出版）』▽『渡辺正臣著『富士山・富士五湖』（1989・実業之日本社・ブルーガイドブックス）』▽『諏訪彰編『富士山――その自然のすべて』（1992・同文書院）』▽『つじよしのぶ著『富士山の噴火――万葉集から現代まで』（1992・築地書館）』▽『渡辺健二著『富士山の植物たち』（1993・静岡新聞社）』▽『青弓社編集部編『富士山と日本人』（2002・青弓社）』▽『志崎大策著『富士山測候所物語』（2002・成山堂書店）』▽『『平野榮次著作集　富士信仰と富士講』（2004・岩田書院）』▽『富士火山編集委員会編『富士火山（改訂版）』（2011・日本火山学会）』▽『森下晶著『富士山』（講談社現代新書）』▽『永原慶二著『富士山宝永大爆発』（集英社新書）』

富士山
国内最高の標高（3776m）と美しい山容を誇る日本の象徴。古くから信仰の対象として崇められてきた霊峰である。季節によって、また見る方角によって、さまざまな姿を見せる。富士箱根伊豆国立公園の中心をなす。写真は静岡県側上空より撮影。世界文化遺産「富士山―信仰の対象と芸術の源泉」の一部（2013年登録）　静岡県富士宮市・富士市・裾野市・御殿場市・駿東郡小山町／山梨県富士吉田市・南都留郡鳴沢村©Shogakukan">

富士山

富士山の地質断面図

宝永火口

三保松原と富士山

赤富士

ダイヤモンド富士

富士山と茶畑

富士山山開き

『名勝八景　冨士暮雪』
歌川豊国（2世）画国立国会図書館所蔵">

『名勝八景　冨士暮雪』

『冨士三十六景　駿河三保之松原』
歌川広重画　1858年（安政5）国立国会図書館所蔵">

『冨士三十六景　駿河三保之松原』