Ishizuchi Mountains

A mountain range that stretches along the eastern border between Kochi and Ehime prefectures. It occupies the western half of the Shikoku mountain range. The Ishizuchi Mountains were formed by the overlapping of an east-west rising axis that stretches from the Houou Mountains to the Sadamisaki Peninsula, and a north-south rising axis that stretches from the Takanawa Peninsula to Cape Ashizuri. There are some sharp, towering rock peaks formed by the erosion of Tertiary volcanoes, but at Saragamine, Omoriyama, and Kamegamori, peneplains or fossil peneplain remains are situated on top, giving the mountain a gentle appearance. However, in areas with greater uplift, the forces of erosion are also strong, and steep valleys with steep slopes have developed. The northern side of the mountain range is joined by the Median Tectonic Line fault, creating a towering fault scarp with a vast zone of steep slopes. On the southern side of the mountain range, gentle slopes continue widely, and a mature mountain range continues with the mountain shape characteristic of the outer Sanbagawa metamorphic rock belt. These mountain ranges are made up of Ishizuchi Tertiary strata, such as lake deposits, volcanic deposits, and lava, on top of the crystalline schist basement. Steep Kaishun valleys have developed around the mountain range, and there are many rapids and waterfalls.

[Kazuo Fukaishi]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

高知・愛媛県境東部に連なる山脈。四国の脊梁(せきりょう)山脈の西半を占める。法皇(ほうおう)山脈から佐田岬半島に達する東西系上昇軸と、高縄半島から足摺(あしずり)岬に至る南北系上昇軸の地波が重なり石鎚山脈が形成された。第三紀の火山の侵食によってできた、鋭くそそり立つ岩峰もあるが、皿ヶ嶺(みね)、大森山、瓶(かめ)ヶ森などには準平原または化石準平原遺構がのっていて、なだらかな山容をみせる。しかし上昇量が大きい周辺では侵食の営力も強く働き、傾斜の大きい険しい谷が発達する。山脈の北側は中央構造線の断層でくぎられ、広大な急斜面帯が続く断層崖(がい)がそそり立っている。一方山脈の南面では、緩斜面が広く続き、外帯の三波川(さんばがわ)変成岩帯特有の山容をもった壮年期山地が続く。これらの山地は基盤の結晶片岩の上に湖成堆積物(たいせきぶつ)、火山性堆積物、溶岩などの石鎚第三系の地層をのせている。山脈の周囲では急勾配(こうばい)の回春谷が発達し、急流や滝が多い。

［深石一夫］

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