Kofu Basin

A tectonic basin located in the center of Yamanashi Prefecture. The basin floor is 250 to 400 meters above sea level. In the center, it is about 25 kilometers east to west and 15 kilometers north to south. It is a basin on the Itoigawa-Shizuoka Tectonic Line, which cuts the central highlands of Honshu from north to south, and is connected to the Nagano Basin, Matsumoto Basin, and Suwa Basin. The fault between it and the vanguard mountain range of the Chichibu Mountains to the north is unknown, but it is limited by faults to the Kanto Mountains to the east, the Misaka Mountains to the south, and the Koma Mountains, which are the vanguard of the Akaishi Mountains to the west. Alluvial fans or composite alluvial fans have developed in the foothills of these mountains, and the Midaigawa Alluvial Fan and the Kanegawa Alluvial Fan are known to be typical ones. The main rivers flowing through the basin are the Kamanashi River in the west and the Fuefuki River in the east, which join in the southwest of the basin and become the Fuji River at Kajikazawa. The area around this confluence is an alluvial plain. Agricultural land use in the Kofu Basin has changed significantly over the years, but in recent years, fruit cultivation (peaches, grapes, etc.), centered on Kyoto (the eastern part of the basin) and Kyosei (the western part of the basin), has expanded to the bottom of the basin, which was once a rice paddy area, the northeastern part of the basin, which is a mulberry field area, and the southern and northwestern slopes of the volcanic foothills of the basin. This is the result of efforts to earn high income from small amounts of farmland, due to the inland climate with annual precipitation of around 70% of the national average, cold winters and high summers. The central city is Kofu City.

[Minoru Yoshimura]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

山梨県中央部に位置する構造盆地。盆地底の標高は250～約400メートル。中央部で東西約25キロメートル、南北約15キロメートル。本州中央高地を南北に切る糸魚川‐静岡構造線(いといがわしずおかこうぞうせん)上の盆地で、長野盆地、松本盆地、諏訪(すわ)盆地に続くもの。北側の秩父(ちちぶ)山地の前衛山地との間の断層は不明であるが、東の関東山地、南の御坂(みさか)山地、西の赤石(あかいし)山脈前衛の巨摩(こま)山地とは断層により限られる。これら山地の山麓(さんろく)部には扇状地あるいは複合扇状地が発達し、御勅使川扇状地(みだいがわせんじょうち)、金川扇状地(かねがわせんじょうち)は模式的なものとして知られる。盆地内を流下する主要河川は西部では釜無川(かまなしがわ)、東部では笛吹川(ふえふきがわ)で、これらは盆地南西部で合流し鰍沢(かじかざわ)で富士川となり流出する。この合流点付近は沖積原となっている。甲府盆地の農業的土地利用は時代による変動が著しいが、最近では峡東(きょうとう)（盆地東部）と峡西（盆地西部）を中心とする果樹栽培（モモ、ブドウなど）が、かつての水田地帯である盆地底部、桑園地帯である盆地北東部、盆地南部あるいは盆地北西部の火山山麓斜面にまで拡大しつつある。これは、内陸性気候で年降水量が全国平均の70％前後で、かつ冬寒く夏高温であることにより、狭い農地からいかに高収入を得るかの努力の結果である。中心都市は甲府市。

［吉村　稔］

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