Mount Yakedake

An active volcano on the border between Nagano and Gifu prefectures. It is one of the peaks in the Hida Mountains (Northern Alps), and rises to the west of Kamikochi. It has a southern and northern peak, and the triangulation point at 2,455 meters above sea level is the southern peak. The northern peak is 2,444 meters above sea level. It is an andesitic stratovolcano with a lava dome shape, based on paleozoic strata and granite. There is a crater with a diameter of about 300 meters at the summit, but fissure eruptions also occur on the mountainside. There are about 10 recorded eruptions, from 1585 (Tensho 13, when more than 300 houses were buried by volcanic mudflows) to the fissure eruption in 1962-1963 (Showa 37-38) (four people were injured by volcanic rocks), but most were steam explosions, which often caused volcanic mudflows. In the eruption on June 6, 1915 (Taisho 4), a large mudflow dammed the clear waters of the Azusa River, forming Taisho Pond. Due to its active sulfuric activity, it is called Mount Iodake or the "incense burner of the Alps." No trees grow on the mountainside, and the view through the larch forest from Kappa Bridge in Kamikochi is wonderful. During heavy rains, the volcanic gravel layer collapses, causing debris flows to rapidly fill Taisho Pond, and in recent years, dredging of the bottom of the pond has been required. It belongs to the Chubu Sangaku National Park, and it takes five hours round trip to reach the summit from Kamikochi via Nakao Pass. However, due to restrictions imposed by collapses and the release of toxic volcanic gases, only the northern peak can be climbed.

[Akira Suwa]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

長野・岐阜県境にある活火山。飛騨山脈(ひださんみゃく)（北アルプス）の一峰で、上高地(かみこうち)の西にそびえる。南峰と北峰があり、標高2455メートルの三角点は南峰。北峰は2444メートル。古生層や花崗(かこう)岩を基盤とする、溶岩円頂丘状の安山岩質成層火山。山頂に直径約300メートルの火口があるが、山腹でも割れ目噴火する。1585年（天正13。火山泥流で家屋埋没300余）から、1962～1963年（昭和37～38）の割れ目噴火（噴石で負傷者4人）まで、約10回の噴火記録があるが、ほとんどが水蒸気爆発で、しばしば火山泥流を生じた。1915年（大正4）6月6日の爆発では、大泥流が梓川(あずさがわ)の清流をせき止め、大正池ができた。硫気活動が盛んで、硫黄岳(いおうだけ)とか「アルプスの香炉」と称され、山肌に樹木が育たず、上高地の河童(かっぱ)橋などからカラマツ林を通しての眺望はすばらしい。豪雨時に火山砂礫(されき)層が崩壊し、土石流が大正池を急速に埋め立て、近年は池底の浚渫(しゅんせつ)に追われている。中部山岳国立公園に属し、上高地から中尾峠経由で頂上へは往復5時間の行程。なお、崩落と火山性有毒ガスの発生に伴う規制により、北峰のみ登頂可能。

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