Mt. Fuji's Nature
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Mt. Fuji's geography and geologic features : Mt. Fuji's Nature : top
1Mt. Fuji's climate
2Mt. Fuji's geography and geological features
2Mysterious groundwater and springss

Mt. Fuji's geography and geologic features

Mt. Fuji's composition

    Mt. Fuji is one of the few large composite volcanoes made of basalt in the world. Its current beautiful cone shape was caused by eruptions during three periods: Komitake, Kofuji, and Shinfuji.

    An explosive Edo Period eruption 1707 created Hoei Crater and formed the huge volcanic ash field on the east side. Mt. Fuji has been dormant since then.

Mt. Fuji's location and form

    Typical of a composite volcano, Mt. Fuji has a smooth slope and a wide spreading base, creating a beautiful skyline as it narrows to a magnificent peak.

    It is said that the main cause of Mt. Fuji's volcanic activity is the Pacific Plate sinking under the bottom of the Philippine Plate, just like the other volcanoes in the Fuji volcanic belt.
    Three plates overlap each other near Japan, and Mt. Fuji is located where the Nankai Trough is being bent northwards due to the Izu Peninsula's impact on Honshu.

    Plate map

Geological Characteristics

    Mt. Fuji has a composite structure due to multiple accumulations of lava, lapilli, and ash from repeated eruptions.
    It is unique that Mt. Fuji's volcanic product is basalt, given that most other Japanese volcanoes are made of andesite.

Shinfuji's Volcanic History

Period Activity
11,000 to 8,000 years ago Released huge amounts of lava from the peak crater (ancient lava flows)
8,000 to 4,500 years ago Ash gushed intermittently from the peak crater (quiescence)
4,500 to 3,000 years ago Large-scale lava and small-scale ash gushed from the peak crater and side volcanoes (mid-term lava stream).
3,000 to 2,000 years ago Frequent explosive eruptions, mainly from the peak crater
2,000 years ago to recent years Repeated gushes of lava (new period stream) and ash from the side volcanoes. Huge eruptions occur approximately once every 500 years. The eruptions recorded in 800 , 864 and 1707 were especially large.

Rare geography and geological phenomena

    Basalt lava has low viscosity and spreads easily over a broad area, creating a unique landscape of many lava caves and tree molds.


Osawa collapse

    Mt. Fuji is a relatively young volcano, having gained its present shape approximately 10,000 years ago. However, valleys have been created by corrosion from wind, rain and snow. The largest, Osawa, extends from the right below the west side peak and is said to have been first created approximately 1,000 years ago.

    It is thought that a large runoff like the Osawa collapse remains because of few ash falls are present on the west side but ash covers the east side with each eruption.

    Osawa collapse
    "Osawa collapse"

Lava caves and tree molds

    It is thought that lava caves are created by a core lava flow that solidifies slowly and the gas emissions created during solidification. They show us what it looks like when lava, nearly 1,000oC during flow, gradually cools and solidifies. Lava tree mounds occur when lava burns trees and leaves hollow areas and inform us what forest conditions and lava flows were like at the time.

    Lava cave in Inno, Gotenba-shi
    "Inno Lava Tunnel, Gotemba City"

    {Source: The Nature and Blessings of Mt. Fuji (Shizuoka Prefecture)}