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Shikotsu-Tōya NP., Hokkaido
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In its fastest phase, Showa Shinzan’s central lava tower rose 1–2 m a day, averaging about 0.6 m. By September 1945, it had reached 406.9 m above land that had been farmland.
As nearby Fukaba was ruined by ground rising as much as 50 m, railway workers repeatedly shifted the tracks east to keep the line running. The growing volcano rewrote a community’s map.
The red-brown surface is old clay baked hard by the rising dome, not simply lava. Rounded river stones found partway up the slope are clues that the mountain swallowed a former river landscape.
During the Pacific War, strict press controls largely silenced reports of Showa Shinzan’s eruption in newspapers and on radio. Yet local postmaster Masao Mimatsu kept a detailed record of its birth.
With camera film scarce, Mimatsu made a fixed viewing station: chin on a wooden rest, fishing threads aligned with a distant eave. He sketched the changing skyline from the same angle each day.
Mimatsu’s layered sketches became the Mimatsu Diagram, presented at an international volcanology meeting in Oslo in 1948. Researchers praised the record and named the chart for the local postmaster who made it.
In 1946, Mimatsu spent his own money to buy the newly formed mountain and protect it from development. Showa Shinzan became a Special Natural Monument in 1957, preserving a volcano and the record of its birth.
Showa Shinzan reached 406.9 m when its growth stopped in 1945; today its listed summit is about 398 m. Erosion and settling after magma supply ceased have lowered it by roughly 9 m.
The bronze figure at the mountain’s foot shows Mimatsu looking through a survey instrument. Its base bears 麦圃生山, roughly a mountain born from a wheat field—a tiny caption for a huge transformation.
