Historic eruptions of Mount Fuji
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Historic eruptions of Mount Fuji (富士山の噴火史:Fuji-san no funka-shi)
Mount Fuji is the tallest volcano in Japan, and also the volcano with the greatest volume. It is believed to have grown greatly in volume in the last 100,000 years, so it can be classified as a "young volcano".
The mountain as it appears now is the "New Fuji volcano", which began to erupt about 10000 years ago. Under the "New Fuji volcano" lie the "Komitake volcano", which became active 700,000 years ago, and the "Old Fuji volcano", which was active between 100,000 years ago and 1000 years ago.
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[edit] Komitake
It is known that there has been much volcanic activity in the vicinity of Mount Fuji for several million years. 700,000 years ago, in the location occupied by the current Mount Fuji, a volcano known as Mount Komitake (小御岳火山?), literally meaning "small mountain volcano", became active. Around this time, another volcano, Mount Ashitaka (愛鷹山?), in the area to the south-east of Mount Fuji, was also highly active. The peak of the ancient volcano, Komitake, can be seen from the north face of Mount Fuji at the fifth station, about 2300 meters above sea-level.
[edit] Old Fuji
Around 100,000 years after becoming inactive, Komitake entered another period of activity. The volcano in this period is known as Old Fuji (古富士 kofuji?). Old Fuji was characterised by explosive eruptions, throwing out large quantities of scoria, volcanic ash and lava, forming a large mountain which reached a height of 3,000m.
[edit] New Fuji
Following the Old Fuji period, there were about 4000 years of inactivity, ending at around 5000 years ago, when Mount Fuji became active again; this period is known as New Fuji (新富士 shinfuji?), and continues to the present day. Eruptions of New Fuji exhibit phenomena such as lava flows, magma, scoria, volcanic ash, collapses and side eruptions, leading it to be called "a department store of eruptions". Ash from New Fuji is often black, and eruptions are new in terms of geological layers. Valuable data on the activity of Mount Fuji is recorded in Japanese historical documents dating from the 8th century onwards. It exhibits a range of representative eruptions.
[edit] Explosive eruptions before the activity 3000 years ago
There were 4 explosive eruptions in the Jomon era, which are known by the names Sengoku scoria (Sg), Ōsawa scoria (Os), Ōmuro scoria (Om) and Sunazawa scoria (Zn). As the wind normally blows from the west in the area of Mount Fuji, most ejectants fall to the east, but in the case of the Ōsawa scoria, they were carried on the east wind, as far as the vicinity of Hamamatsu.
[edit] The Gotenba mud flow
About 2300 years ago the east face of the volcano collapsed, and liquid mud flowed down to Gotenba area as far as the Ashigara plain in the east and the Suruga bay across Mishima city in the south. This incident is now called the (Gotenba mud flow (御殿場泥流 Gotenba deiryū?). Liquid mud piled up over an area as wide as the city area of Mishima.
[edit] Jōgan eruption
In 684 (the 6th year of the Jōgan era) there was an eruption on the north-east side of Mount Fuji, which produced a great amount of lava. Some of the lava filled up a large lake (Senoumi (せの海?)) which existed at the time, dividing it into two lakes, Saiko (西湖?) and Shōjiko (精進湖?). This is known as the Aokigahara lava (青木ヶ原溶岩?), and at present is covered by forest.
[edit] Hōei eruption
The latest eruption, in 1707年 (the 4th year of the Hōei era), was known as the great Hōei eruption. It began 49 days after the Hōei earthquake, which was on the largest scale found in Japan. This eruption was remarkable in that spread a vast amount of volcanic ash and scoria over a region as far away as Edo.
[edit] Records of eruption
17 eruptions of New Fuji have been recorded since 781. Many of the eruptions occurred in the Heian era, with 12 eruptions between 800 and 1083. Sometimes inactive periods between eruptions lasted for hundreds of years, as in the period between 1083 and 1511, when no eruptions were recorded for over 400 years. At present, there have been no eruptions since the Hoei eruption in 1707, around 300 years ago.
[edit] See also
[edit] Reference book
- Fujisan Sono Shizen no Subete (富士山 その自然のすべて?), "Mount Fuji - All About Its Nature", written by Akira Suwa (諏訪彰?) 1992 Dōbunshoin (同文書院?) ISBN 4-8103-4047-3
