Mt. Fuji's Nature / Fujisan Network

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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.

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

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"

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.

"Inno Lava Tunnel, Gotemba City"

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