Kibi Plateau

An elevated peneplain that stretches from east to west between the Seto Inland Sea coastal lowlands and the Chugoku Mountains. It is 200 to 600 meters above sea level. However, it rose up to become a peneplain, and there are several stages of eroded low relief. There are several isolated hill-like peaks on the plateau, including many basalt domes. The characteristics of the Kibi Plateau become quite faint east of the Yoshii River, but are extremely clear in the Yoshii River, Asahi River, and Takahashi River in Okayama Prefecture, and the Ashida River in Hiroshima Prefecture. These rivers flow down the Chugoku Mountains, and cut deeply and meander as they cross the Kibi Plateau, creating beautiful gorges such as Atetsu Gorge, Ikura Gorge, and Taishaku Gorge. Rivers that collect water on the Kibi Plateau initially form shallow valleys with gentle slopes, then at the tipping point they form deep gorges and either merge into the main valley or flow out onto the plains at the southern edge of the Kibi Plateau. The plateau surface is dominated by limestone plateaus such as Atetsudai and Jobodai, and karst topography can be seen. In general, the narrow valley bottoms serve as transportation routes, and the undulating hills on the plateau become pine forests, settlements and farmland have developed on the slopes, while the shallow, wide depressions become marshy rice fields. The climate is cooler than the coastal plains, and in addition to industrial crops such as tobacco, dairy farming and controlled vegetable cultivation are also practiced. Many areas have poor transportation access and are becoming depopulated. In Kibichuo Town, Okayama Prefecture, the prefectural government has planned the construction of the Kibi Plateau City.

[Shogo Yuihama]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

瀬戸内海沿岸低地と中国山地間に東西に延びる隆起準平原。標高200～600メートル。ただし、準平原に至る段階で隆起したもので、何段かの侵食小起伏面がみられる。高原上には残丘状の孤立峰がいくつかあり、なかには玄武岩のドームも多い。吉備高原の特徴は吉井川以東ではかなり希薄になり、岡山県の吉井川、旭(あさひ)川、高梁(たかはし)川、広島県の芦田(あしだ)川の部分できわめて明瞭(めいりょう)である。これらの河川は中国山地を流下し、吉備高原を横断する部分では深く穿入(せんにゅう)蛇行し、阿哲(あてつ)峡、井倉峡、帝釈(たいしゃく)峡などの峡谷美を呈する。吉備高原上で集水する河川は最初は緩勾配(こうばい)の浅い谷をつくり、遷急点からは深い峡谷をなし、主谷に合流するか、吉備高原南縁で平野に出る。高原面には阿哲台、上房(じょうぼう)台などの石灰岩台地があり、カルスト地形がみられる。一般に狭い谷底は交通路の役割を果たしており、高原上の波状の丘は松林となり、斜面に集落や畑地が発達し、浅く広い窪地(くぼち)は湿田となる。沿岸平地より冷涼で、タバコなどの工芸作物のほかに酪農や野菜の抑制栽培なども行われる。交通不便な地が多く過疎化が進んでいる地域が多い。なお、岡山県の吉備中央町には、県の構想による吉備高原都市が建設された。

［由比浜省吾］

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