2 0 0 0 OA 富士山の地質と変貌
- 著者
- 浜野 一彦
- 出版者
- 公益社団法人 東京地学協会
- 雑誌
- 地学雑誌 (ISSN:0022135X)
- 巻号頁・発行日
- vol.91, no.2, pp.69-87, 1982-04-25 (Released:2010-10-13)
- 参考文献数
- 9
- 被引用文献数
- 1
The geological formations of Mt. Fuji are composed of Pre-Miocene, Miocene, Pliocene and Komitake, Fuji volcanic ejecta.The following table shows the geological formations of this region.Pre-Miocene, Miocene and Komitake volcanic ejecta lie beneath Mt. Fuji. These rocks are the foundation of Fuji volcano.The first building of Fuji volcano started by Kofuji volcanic mudflow which covered the Komitake volcano and older rocks. The second eruption is made up of a sequence of Younger volcanic ejecta, which cover on alluvium sequence.The sequence of ejecta is L1-T1-L2-T2-L3-L4-T3 layers, except for L4 and T3 layers they all erupted from summit fire crater. L-layer is composed of the lava and tephra alternation and T-layer, which has the most of tephra. These limits make up the stratified volcano.The flanks of mountain are sculptured by a number of radial valleys but they not have surface streams. The largest valley is “Osawa” and the second is “Yosidaosawa”, both integrated these valleys are now growing. These valley are eroded by streams of the heavy rainfall, flow of underground water and by snowslides. Osawa is a V-type erosion valley and Yoshidaosawa is a U-type wallerosion valley.On the flank of the mountain, rainwater sinks into the ground and is stored on the surface of the unpermeable layers (Kofuji volcanic mudflow) as the underground water. It runs downward and flows out at the mountain foot. From the cliff, which outcrips at the top of Yoshidaosawa, large rock fragments fall and roll on the valleyfloor. Summer in 1980, twelve persons were killed by such rockfall. This rockfall happened by the increase of the undergroundwater pressure which made the rock fragments on the near cliff unstable and caused the disasterous rockslides.
