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Fuji-Hakone-Izu NP, Tokyo
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Kozushima’s water legend begins in Mt. Tenjo’s sacred hollow, Inai-ga-sawa: island gods divided water by arrival order, and the late god of Toshima splashed the leftovers—creating Kozushima’s many springs, the tale says.
Mt. Tenjo was born in 838 in a dramatic sequence: pyroclastic flows and surges, ash fall, then a lava dome. Its eruption-built summit still holds crater basins, ponds and striking white volcanic sands.
Mt. Tenjo’s 838 eruption left a pale pumice layer across neighboring Miyakejima. Geologists use that distant volcanic “time stamp” to work out which of Miyakejima’s lava and ash layers came before or after it.
Mt. Tenjo’s white “desert” is volcanic ground. Oshima azaleas took root first after the eruption; other plants followed, and strong winds shaped the greenery into scattered, rounded islands.
The heart-shaped outline of Fudo Pond appears only at certain water levels. Island fishers once revered the pool, and a small shrine to a dragon deity still stands on its central islet.
Mt. Tenjo’s crater ponds shelter Izunoshima-hoshikusa, an annual wetland plant listed as Endangered IB in Japan. A 2018 survey estimated thousands in one mapped area, yet its assessed 20-year extinction risk is at least 20%.
On the approach to Mt. Tenjo’s Kuroshima trail, Yamanokami Cold-Air Cave sends cool air out of the ground in summer. The park plan explains the breeze: underground and outdoor temperatures differ.
