Miyakonojo Basin

A basin in the southwest of Miyazaki Prefecture. It is a vast inland basin with an area of ​​about 760 square kilometers, including two cities and two towns (one of which is in Kagoshima Prefecture) centered on Miyakonojo City. The elevation of the bottom of the basin is about 140 meters. The west is bounded by the Kirishima volcano, the east by the Nichinan mountain range, and the north and south by hills and a shirasu plateau. It is a structural lowland, and in the Pleistocene (Pleistocene) there was a deposition of shirasu from the Aira volcano, and the formation of a lake. Later, as the Oyodo River found its outlet in the Miyazaki Plain, it became land and became the basin it is today. The western part of the basin is a secondary shirasu plateau of lacustrine deposits, and the eastern part is dominated by alluvial fan terraces, and alluvial plains are limited to the rivers. The Oyodo River flows north, collecting many tributaries within the basin. Covered by whitebait and Kirishima volcanic ash, the area has a large amount of farmland, and in addition to field crops such as sweet potatoes and taro, green corn for feed and pasture cultivation are thriving, along with livestock (milk and meat cattle and pigs). The basin also experiences unusual weather conditions, including frequent fog and frost, which are used to cultivate tea. Tourist attractions include Sekinoonotaki Falls, with its many potholes, and the cherry blossoms of Mochio.

[Junichi Yokoyama]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

宮崎県南西部にある盆地。都城市を中心に二市二町（うち一市は鹿児島県）を含む広大な内陸盆地で、面積は約760平方キロメートル。盆地底の標高は約140メートル。西部は霧島(きりしま)火山、東部は日南(にちなん)山地、北部、南部は丘陵、シラス台地で限られる。構造性低地で、更新世（洪積世）に姶良(あいら)火山起源のシラス堆積(たいせき)、湖の形成があり、のち大淀川(おおよどがわ)が宮崎平野に排水口をみいだすに伴い陸化、現在の盆地となった。盆地西部は湖成層の二次シラス台地、東部は扇状地性の段丘面が広がり、沖積平野は河川沿いに限られる。大淀川は盆地内で多数の支流を集め北流する。シラス、霧島火山灰に覆われるため畑地が広く、サツマイモ、サトイモなど畑作物のほか、飼料用の青刈りトウモロコシ、牧草栽培が家畜飼育（乳・肉用ウシ、ブタ）とともに盛んである。また、盆地の特異な気象条件として霧、霜の発生が多く、これを利用する茶の栽培も知られる。観光地は、甌穴(おうけつ)の発達する関之尾滝(せきのおのたき)、母智丘(もちお)の桜などである。

［横山淳一］

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