Owakudani - Owakudani

This valley is home to a group of sulfur vents in Hakone-machi, Ashigarashimo-gun, in the southwest of Kanagawa Prefecture, and is one of the water sources of the Hayakawa River. It is also called "Owakidani" and was formerly known as Ojigoku. In 1872 (Meiji 5), Emperor Meiji renamed Kojigoku when he bathed there, and this place was named Owakudani, following his example. Located on the northern slope of the central crater cone Kamiyama (1,438 meters), the highest peak of the Hakone volcano, this valley was formed by the explosion of Kamiyama (Owakudani explosion) at the end of the Hakone volcanic activity, and the group of fumaroles are remnants of volcanic activity. Of the two valleys in Owakudani, Enmadai in the southwest continues to be active, actively spewing steam containing sulfur, and needle-shaped crystals of sulfur can be seen around the hot mud and sulfur vents. However, Jigokusawa in the northeast has become less active and only spews hot air.

Owakudani has long been one of the sacred places of Hakone, along with Kowakudani (Little Jigoku), and was considered to be the precincts of Hakone Gongen (Hakone Shrine). High-temperature, acidic hot springs gush out, and when eggs are put into them, they become black-shelled boiled eggs, one of the Hakone specialties. A stone chamber has also been built at the hot air eruption point of the now inactive Jigokuzawa, and water is poured into it and heated naturally to produce a hydrogen sulfide spring containing argon, which is then sent to Sengokuhara Onsen and Gora Onsen. In 1972 (Showa 47), the town-run Owakudani Nature Museum was established in front of the Hakone Ropeway Owakudani Station, and exhibited materials on the growth, geology, biology, hot springs, and famous historical sites of the Hakone volcano (closed in 2003).

[Yukio Asaka]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

神奈川県南西部、足柄下(あしがらしも)郡箱根町(はこねまち)にある硫気孔群のある谷で、早川の水源の一つ。「おおわきだに」ともいい、古くは大地獄といっていた。1872年（明治5）明治天皇が小地獄へ入湯のおりに、そこを小涌谷と改めたのにならい、ここも大涌谷とした。箱根火山の最高峰、中央火口丘神山(かみやま)（1438メートル）の北斜面の中腹にあたり、箱根火山活動の末期におきた神山の爆裂（大涌谷爆裂）によってできた谷で、噴気孔群は火山活動の名残(なごり)を示すもの。大涌谷の二つの谷のうち、南西の閻魔台(えんまだい)はいまも活動を続けて硫気を含んだ水蒸気を盛んに噴出し、熱泥や硫気孔の周りに硫黄(いおう)の針状結晶がみられる。しかし、北東の地獄沢は活動が衰え、熱気を噴き出すにとどまっている。

　大涌谷は大昔から小涌谷（小地獄）とともに箱根の霊境の一つで、箱根権現(ごんげん)（箱根神社）の境内とされていた。高温、酸性の温泉が湧(わ)き出し、卵を入れると殻の黒いゆで卵となり、箱根名物の一つ。また活動の衰えている地獄沢の熱気の噴出点には石室(いしむろ)が設けられ、水を注いで自然加熱されて含緑礬(りょくばん)硫化水素泉とされ、仙石原温泉(せんごくはらおんせん)、強羅温泉(ごうらおんせん)へ送られている。1972年（昭和47）箱根ロープウェイ大涌谷駅前に町立の大涌谷自然科学館が設立され、箱根火山の成長・地質・生物・温泉、名所旧跡などの資料が展示されていた（2003年閉館）。

［浅香幸雄］

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