Yubari Mountains - Yubarisanchi

This mountain range, together with the Hidaka Mountains to the east, forms the backbone of the central southern half of Hokkaido. It lies between the Sorachi River to the north and the Saru River to the south, and is divided into two tilted masses, east and west, by the north-south line of the Ashibetsu River and Shuparo River. The eastern mass is made of rocks from the ancient Kamuikotan System and the Mesozoic Cretaceous Period, and in the center is a series of mountain ridges with mature topography, including Mt. Ashibetsu (1,726 meters) and Mt. Yubari (1,668 meters), and it borders the Furano Basin to the east by a fault scarp. The western mass is made of Tertiary layers, is lower in altitude than the former, and faces the Ishikari Plain. Here, coal-bearing layers in the Tertiary layer run from north to south, and coal outcrops exist along the rivers that cut through them, which led to the development of the Ishikari coalfields after the Meiji period. Dams were also built in the river valleys to be used as power sources. In 1996, the "Alpine Plant Community and Serpentine Melange Zone of Mt. Yubari" in the Furano Ashibetsu Prefectural Natural Park area was designated a national natural monument.

[Ichiro Kashimura]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

北海道中央南半の骨格を東の日高(ひだか)山脈とともに形成する山地。北は空知(そらち)川、南は沙流(さる)川の間を占め、南北方向の芦別(あしべつ)川―シュウパロ川の線で東西二つの傾動地塊に分けられる。東の地塊は古い神威古潭(かむいこたん)系や中生代白亜紀層の岩石からなり、中央部には芦別岳（1726メートル）、夕張岳（1668メートル）など壮年地形の山嶺(さんれい)が連なり、断層崖(がい)で東の富良野(ふらの)盆地に接する。西の地塊は第三紀層からなり、前者より高度も低くなって石狩(いしかり)平野に臨む。ここには第三紀層中の夾炭(きょうたん)層が南北に連なり、これを刻む河川沿いに石炭の露頭があり、明治以降の石狩炭田開発につながった。また河谷にはダム建設も進み電源に利用される。富良野(ふらの)芦別道立自然公園域で、1996年（平成8）「夕張岳の高山植物群落及び蛇紋岩メランジュ帯」が国の天然記念物に指定された。

［柏村一郎］

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