The Mountain That Japan Hid From The World

Inside Shikotsu-Toya National Park, on the island of Hokkaido, not far from the active stratovolcano, Mount Usu, is a 400-meter-high volcanic peak called Showa-Shinzan. Showa-Shinzan is the youngest mountain in Japan. It emerged from a wheat field on 28 December 1943 with strong shaking and hot lava. As the molten magma broke through the surface, it raised the plain and over the next two years the lava dome continued to grow until it reached a height of 398 metres.

Showa-Shinzan arose when Japan was fighting the Allies in World War II. At a time when the entire country was in crisis, the appearance of the volcano was taken as a bad omen by superstitious people. Authorities tried to suppress it and requested locals to keep the mountain a secret. But Masao Mimatsu, a postmaster who lived nearby, began observing and recording the volcano's progress. Due to Japan's war effort, basic scientific material was unavailable and Mimatsu had to improvise. The notes he took and the sketches he made of Shōwa-Shinzan are the only records available to geologists of the formation of this mountain.

Masao Mimatsu draws several fishing lines horizontally across two vertical beams in his post office. He observed the evolution of the volcano through these lines – they were acting as guiding lines – and made outlines of Showa-Shinzan at different times as the dome grew. When he presented his data and sketches at the World Volcanology Conference in Oslo in 1948, professional volcanologists praised his work. His papers were known as "Meimatsu Diagrams" and for them he received the first Hokkaido Cultural Prize.

Mimatsu also used all his savings to buy the entire land where the volcano stood so that he could study the volcano more thoroughly. Some say this happened while the volcano was still growing. Others say he bought the land after the volcano stopped erupting. Whatever the truth, Mimatsu became the owner of the volcano and to this day the volcano remains on private property despite the Japanese government declaring it a Natural Monument of Japan – a rarity anywhere in the world.

Masao Mimatsu is honored by the Mimatsu Masao Memorial Hall near the Showa-Shinzan site and a bronze statue of him looking through a surveying instrument.