Yokote Basin

Located in the southeastern part of Akita Prefecture, this is the largest basin in the Western Ou Basin chain. It is 60 km north to south and 15 km wide at its widest point from east to west. The eastern edge of the basin is bordered by the Ou Mountains by the Mahirudake fault scarp, and the western edge is bounded by the Dewa Mountains. The Omono River flows north along the western edge of the basin, and joins the Asahi River, the Maruko River, and the Tama River, which cross the Dewa Mountains at the northwestern edge of the basin and flow into the Akita Plain. The basin is 100 meters above sea level in the south and 20 meters at the northwestern end. The floor of the basin consists of a composite alluvial fan below the eastern fault scarp and alluvial land in the west. There are 10 composite alluvial fans lined up north of Yokote City, and the slope is steep from the top to the center of the fan, but the slope becomes gentler at the end of the fan before transitioning to alluvial land. In a typical example of the Marikogawa alluvial fan, concentric contour lines can be seen below the Mahirudake fault scarp, and a row of springs is found along the 45-meter contour line. This row of springs has turned the top, sides and ends of the fan into rice paddies. The water-scarce area in the center of the fan was previously farmland and grassland, where apples and grapes were grown, but has been converted into rice paddies as the Tazawa Canal has been extended. In the southern part of the basin, the Narusegawa and Minasegawa rivers join together to form a large alluvial fan, which has been converted into rice paddies by the excavation of irrigation channels. Furthermore, the narrow, long graben valley in the south is used for orchards. The northern part of the basin is occupied by Daisen City, the central by Yokote City, and the southern part by Yuzawa City, each with their own commercial areas.

[Reijiro Miyazaki]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

秋田県南東部にある西奥羽盆地列最大の盆地。南北60キロメートル、東西の最大幅15キロメートル。盆地の東縁は真昼(まひる)岳断層崖(がい)によって奥羽山脈と接し、西縁は出羽山地(でわさんち)によって限られる。盆地の西縁を雄物川(おものがわ)が北流し、旭(あさひ)川、鞠子(まるこ)（丸子）川、玉川などをあわせ、盆地の北西端で出羽山地を横断して秋田平野に流れる。盆地の標高は南部で100メートル、北西端で20メートルである。盆地床は東部断層崖下の複合扇状地と西部の沖積地とからなり、横手市以北には10個の複合扇状地が並び、扇頂から扇央までは急傾斜をなすが、扇端では緩傾斜となって沖積地に移行する。代表的な鞠子川扇状地では真昼岳断層崖下に同心円状の等高線がみられ、等高線の45メートルの地点に沿って湧泉(ゆうせん)列がある。この湧泉列によって扇頂、扇側、扇端は水田化した。扇央の乏水地域は畑地、草地で、リンゴ、ブドウなどを栽培するが、田沢疎水の延長に伴い水田化されている。盆地南部は成瀬川、皆瀬(みなせ)川が合流して大扇状地をつくり、用水路の開削によって水田化されている。さらに南部の狭長な地溝帯は果樹園に利用されている。盆地北部を大仙市(だいせん)、中央を横手市、南部を湯沢市が占め、それぞれ商圏をもっている。

［宮崎禮次郎］

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