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Fuji-Hakone-Izu NP, Kanagawa
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Black eggs have a chemistry plot twist: a 2023 study found their dark shell film rich in carbon, nitrogen, sulfur and protein-like material—not the iron sulfide long assumed. It browns within days.
The “7 years of extra life” promise has a local spiritual link: according to the black-egg maker, the longevity legend grew around Owakudani’s Enmei Jizō; the lucky number 7 was added later.
The peak behind Owakudani, Kanmurigatake, is a volcanic afterthought: after Mt. Kamiyama’s north side collapsed about 3,000 years ago, rising magma built a new lava dome in the scar.
That ancient collapse reshaped Hakone: its debris dammed the Hayakawa River and formed Lake Ashi. Near Ubako, giant rocks such as Kintaro-iwa are chunks of the fallen mountain.
Owakudani’s geothermal heat became an industry: in 1933, Hakone’s hot-spring supply business began using volcanic steam to heat mountain water into bathwater for nearby onsen areas.
The sulfurous vents once earned Owakudani the name Ōjigoku, or “Great Hell.” It was renamed Owakudani in the Meiji era in connection with an imperial visit to Hakone.
The bleached trees tell a recent story: gases released during the very small 2015 eruption killed surrounding trees, while only plants tolerant of volcanic gas and acidic soil can persist in Owakudani’s fumarole field.
When Hakone’s volcanic activity intensified in 2015, Owakudani’s 700m Nature Research Trail closed for almost 7 years. It reopened March 28, 2022, with guided entry and shelters from volcanic rocks.
