Onioshidashi - Onioshidashi

The name of the lava distributed on the northern slope of Mt. Asama, towering over the border between Nagano and Gunma prefectures, at an altitude of 1,200 to 2,100 meters in Tsumagoi Village, Agatsuma County, Gunma Prefecture. It is the solidification of lava flows that erupted in the great explosion of Mt. Asama on July 8, 1783 (Tenmei 3). It is about 5 kilometers long from north to south and about 1 to 2 kilometers wide from east to west, and traces of three lava flows from that time can be seen along the slope from the summit, with the ends being intricate. The rock is complex pyroxene andesite, and with huge and oddly shaped rocks piled up and a few small plants scattered here and there, it is an extremely scenic spot. Nearby, you can see the Mt. Asama lava tree molds, a special natural monument, and the breadcrumb-shaped volcanic bombs that erupted at the same time. The area belongs to Joshinetsu Kogen National Park, and in the center of the park is the town-run Asama Garden and Volcano Museum, from which you can view the lava flows. Buses can be taken from JR Hokuriku Shinkansen Karuizawa Station, Agatsuma Line Manza/Kazawaguchi Station, and Shinano Railway Nakakaruizawa Station.

[Murakami Sadao]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

長野・群馬県境にそびえる浅間山(あさまやま)の北斜面、群馬県吾妻(あがつま)郡嬬恋村(つまごいむら)の標高1200～2100メートル内外に分布する溶岩の名称。1783年（天明3）7月8日の浅間山の大爆発で噴出した溶岩流が凝固したもの。南北の長さ約5キロメートル、東西の幅約1～2キロメートルで、山頂から斜面に沿って当時の3条の溶岩流の跡がみえ、末端部は入り組んでいる。岩質は複輝石(ふくきせき)安山岩で、巨岩怪石が重なり、わずかに矮小(わいしょう)な植物が点在するだけで、すこぶる奇勝である。付近には特別天然記念物の浅間山溶岩樹型や、同時に噴出したパン殻(がら)状火山弾もみえ、上信越高原国立公園に属し、中心部に溶岩流群を展望できる町営の浅間園や火山博物館がある。JR北陸新幹線軽井沢駅、吾妻線万座(まんざ)・鹿沢口(かざわぐち)駅、しなの鉄道中軽井沢駅からバスが通じる。

［村木定雄］

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