Mount Myoko

It is the main peak of the Myoko volcanic group, located in the southwest of Niigata Prefecture, on the border with Nagano Prefecture. It is 2,454 meters above sea level and belongs to Myoko-Togakushi Renzan National Park. It is a double volcano at the northern end of the Fuji volcanic belt, and its body is made of pyroxene andesite lava, with its circular central crater cone called Mt. Myoko. The calderas of Mt. Kanna, Mt. Maeyama, Mt. Akakura, and Mt. Kuruwadake, which are made up of old lava flows, are 2,000 meters high somma mountains. There is a narrow crater plain between the central cone and the mountain, and there are abundant hot spring sources with active fumaroles called Minami Jigokudani and Kita Jigokudani, from which hot spring water is drawn to the hot spring resorts at the foot of the mountain. The water from the crater floor breaks through the outer rim of the volcano on the east side to form crater rapids such as the Otagiri River and the Shirotagiri River, and downstream forms a deep gorge with a typical Tagiri topography before flowing into the Seki River. In 1978 (Showa 53), the outer rim wall upstream of the Shirotagiri River collapsed due to melting snow, causing a huge mudslide that destroyed the Shin-Akakura hot spring town and villas, causing great damage with 13 deaths, and filling up the Tagiri topography. The main trailhead is Tsubame Hot Springs, and there is also a traverse course across the caldera to Hiuchi and Yakeyama.

[Hisao Yamazaki]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

新潟県南西部、長野県境にある妙高火山群の主峰。標高2454メートルで妙高戸隠連山国立公園に属する。富士火山帯の北端にあたる二重式火山で、山体は輝石安山岩質溶岩からなり、円頂の中央火口丘を妙高山という。古い溶岩流から構成されるカルデラの神名(かんな)山、前山(まえやま)、赤倉山、廓岳(くるわだけ)は2000メートル級の外輪山。中央火口丘との間には狭い火口原があり、南地獄谷(みなみじごくだに)、北地獄谷などとよばれる噴気孔の活動する豊富な温泉源があり、裾野(すその)の温泉郷にはここから引き湯されている。火口原の水は東側の外輪山を破って大田切(おおたぎり)川、白田切(しろたぎり)川などの火口瀬をなし、下流は典型的な田切地形で深い峡谷をなして関川(せきかわ)に流れ込んでいる。1978年（昭和53）には白田切川上流の外輪壁が雪解け水で崩れて大土石流となり、新赤倉温泉街や別荘が倒壊し、13人の死者を出す大被害を与え、田切地形を埋積した。登山口は燕(つばめ)温泉が表口で、カルデラを越えて火打(ひうち)、焼山(やけやま)への縦走コースもある。

［山崎久雄］

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