Odate Basin

A sunken basin located in northern Akita Prefecture, between the Ou Mountains and the Dewa Mountains. It is located upstream of the Yoneshiro River. It is 8 km east to west, 18 km north to south, and has an area of ​​230 square kilometers. The basin is V-shaped and opens to the north. The formation of the basin began with the uplift of the mountains in the late Pliocene (5 million to 1.7 million years ago), and was followed by the subsidence of the basin floor in the early Pleistocene (1.7 million to 10,000 years ago). The basin floor consists of four terraces and the alluvial lowlands along the Yoneshiro River and its tributaries. The deposits on the terraces other than the highest one are pumiceous volcanic ash and its secondary products derived from the Towada Volcano. The alluvial lowlands are used for rice paddies, and there are many beautiful forests of Akita Sugi (Akita cedar) all around. Kuroko deposits are distributed several hundred meters below the surface of the basin, and mines such as Hanaoka, Shakanai, Matsumine, and Ezuri were developed. The center of the basin is Odate City.

[Reijiro Miyazaki]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

秋田県北部、奥羽山脈と出羽(でわ)山地の間にある陥没盆地。米代川(よねしろがわ)の上流に位置する。東西8キロメートル、南北18キロメートル、面積230平方キロメートル。盆地の形は北に開いたV字型である。盆地の形成は鮮新世（500万～170万年前）後期の山地の隆起で始まり、更新世（170万～1万年前）前期の盆地床の沈降による。盆地床は4段の段丘と米代川およびその支流沿いの沖積低地からなる。最高位以外の段丘の堆積(たいせき)物は、十和田火山(とわだかざん)に由来する軽石質火山灰とその二次生成物である。沖積低地は水田に利用され、四周にはアキタスギ（秋田杉）の美林が多い。盆地の地表下数百メートルには黒鉱鉱床が分布し、花岡、釈迦内(しゃかない)、松峰、餌釣(えづり)などの鉱山が開発された。盆地の中心は大館市。

［宮崎禮次郎］

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