Akiyoshidai

Located in Mine City in the western part of Yamaguchi Prefecture, Akiyoshidai is the largest limestone plateau in Japan. It covers an area of ​​approximately 130 square kilometers. It is widely known for its unique karst topography, both academically and as a tourist destination, and the main part of the area is the Akiyoshidai Quasi-National Park. In 2005, the Akiyoshidai groundwater system was registered as a Ramsar Convention wetland.

It is divided into two by the Koto River, and the eastern part is Akiyoshidai in the narrow sense, where Akiyoshido Cave (a special natural monument) and Jigokudai are located. Akiyoshi limestone is a grayish-white, dense rock with many cracks, and contains many types of fusulina and coral fossils, and is known as an index fossil of the Carboniferous and Permian periods of the Paleozoic era. Akiyoshidai is an important research site for elucidating the complex crustal movements known as the Akiyoshi Orogeny. The plateau is 200 to 400 meters high, and is a plateau with small undulations, with countless depressions called dolines. In some places, such as Jigokudai and Tsurugiyama, limestone pillars are exposed widely, creating a unique landscape called Karenfeld. The plateau is burned every year in early spring, turning it into a wide grassland, and some parts are used for pastures and orchards. There are many springs and spring caves at the foot of the plateau, which serve as irrigation water sources for the rice fields around the plateau and are also used for trout farming. Limestone is mined on the plateau west of the Koto River, and factories such as Ube Industries are located at the quarry. Yamaguchi is the number one producer of marble in Japan. There are buses that run from Shin-Yamaguchi Station on the Tokaido-Sanyo Shinkansen line and other stations.

[Hajime Miura]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

山口県西部、美祢(みね)市にある日本最大の石灰岩台地。面積は約130平方キロメートルに及ぶ。特異なカルスト地形の発達によって、学術上、観光上広く知られ、その主要部は秋吉台国定公園となっている。また、秋吉台地下水系は2005年（平成17）に、ラムサール条約登録湿地となった。

　厚東(ことう)川によって二分され、その東部が狭義の秋吉台で、秋芳洞(あきよしどう)（特別天然記念物）や地獄台がある。秋吉石灰岩は、灰白色で割れ目の多い緻密(ちみつ)な岩質で、多種類のフズリナやサンゴなどの化石を含み、古生代石炭紀、ペルム紀（二畳紀）の示準化石として知られる。秋吉台は秋吉造山運動とよばれる複雑な地殻変動を解明する重要な研究地となっている。台面の高度は200～400メートル、小起伏の高原となり、無数のドリーネとよばれる凹地が発達しており、地獄台や剣山(つるぎやま)のように広く石灰岩柱が裸出してカレンフェルトとよばれる特異な景観を示す所もある。台上は毎年春先に行われる山焼きによって広く草原となり一部は牧場や果樹園に利用される。台麓(だいろく)には多くの湧泉(ゆうせん)や湧水洞があって台地周辺の水田の灌漑(かんがい)用水源となり、マスの養殖にも利用。厚東川より西の台地では石灰石の採掘が行われ、採掘場には宇部興産などの工場がある。大理石は全国一の生産をあげる。東海道・山陽新幹線新山口駅などからバスが通じる。

［三浦　肇］

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