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Fuji-Hakone-Izu NP, Tokyo
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In 1986, lava filled Mihara’s central pit completely. Explosive eruptions in November 1987 collapsed the new surface and reopened the shaft; today’s crater is 300–350 m wide and about 200 m deep.
Before the 1777 eruption, this summit held a deep crater about 1 km across—not today’s cone. By April 1778, showers of scoria and volcanic bombs had piled up into the central cone.
The 1986 summit eruption seemed to quiet, then a fissure opened—the first on Oshima in 565 years. A roughly 1 km line of vents formed, sending lava fountains as high as about 1,500 m.
Red light from the hot crater could illuminate clouds above it. Islanders called this glow Gojinka (“sacred fire”) and the crater mihora (“sacred hollow”); one local explanation traces “Mihara” to that old word.
After fissures opened beyond the caldera rim and lava headed toward Motomachi, about 11,000 residents and 2,000 visitors were evacuated by the following day. Residents spent roughly a month away from home.
Dark streaks on Mihara’s slopes mark lava from 1950–51 and 1986. In the 1986 flows, the outer crust cooled and broke into blocks while hot lava kept moving inside—a texture called a‘ā.
Nearly 40 years after the 1986 eruption, colonies of itadori knotweed are appearing again around the summit crater. On bare volcanic ground, plants return in stages, eventually giving way to shrubs and forest.
Mihara-shinzan, the island’s 758 m high point, formed in the 1950–51 eruption. Its northern half later collapsed into the central pit, exposing the inside of this younger volcanic cone.
On October 13, 1957, an explosive blast opened a new summit vent while visitors were near the crater. One person died and 53 were injured.
