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Fuji-Hakone-Izu NP, Tokyo
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On 21 November 1986, fissures opened 500 m from Mihara’s summit vent; 90 minutes later, another broke outside the caldera. Lava reached within 70 m of Motomachi’s crematorium.
In the 1984 Godzilla film, Mihara’s crater became the monster’s trap—2 years before the real 1986 eruption. The National Diet Library preserves production art titled “Godzilla lured to Mihara crater.”
During the 1986 eruption, about 11,000 residents and 2,000 visitors were evacuated to the mainland. Residents stayed away for roughly a month; no one was killed.
Before the 1777 eruption, today’s Mihara was a 1-km-wide crater with no central cone. The 16-year eruption built the mountain and released an estimated 650 million tonnes of material.
Some 1986 scoria from Mihara’s B vents shimmers blue through yellow to red—not from a coating, but from tiny crystals that create structural color. Researchers read it as a record of hot eruption gases and rapid cooling.
Islanders revered Mihara’s erupting fire as Gojinka, “sacred fire”; that image inspired Oshima’s Gojinka Taiko. The group began in 1972, and its signature “midareuchi” debuted at a shrine dedication.
Within about a year of the 1986 eruption, Hachijo-itadori was growing on bare lava. Its three-winged seeds ride island winds; its roots enter cracks, and its fallen leaves help build soil for grasses.
Shinagawa City’s archive preserves an Edo-era entry noting that Mihara’s 1777 eruption lit the night sky across the water, night after night—a striking record of how far its glow could be seen.
Every flow from Mihara’s 1986 eruption was ʻaʻā lava: its outer crust cooled and broke into rough, jagged blocks while the interior kept moving. The A-flow front was about 5 m thick.
