On December 28, 1943, severe earthquakes began shaking the area around Usu-zan and continued to do so until September 1945. In the intervening period a new lava dome rose out of the ground, sometimes at the rate of 1.5m a day. By the time it had stopped growing, Shōwa Shin-zan, the “new mountain” named after the reigning emperor, stood 405m above sea level. The wartime authorities were desperate to hush up this extraordinary event for fear that the fledgling mountain would serve as a beacon for US bomber planes.
Fortunately, Shōwa Shin-zan’s daily growth was carefully documented by local postmaster and amateur volcanologist Mimatsu Masao. After the war, Mimatsu bought the land on which the mountain stood, declaring, “I purchased the volcano to continue my research uninterrupted. I did not buy it to make money. Nor did I buy it for tourists to gawk at.” His efforts were rewarded in 1958 when Shōwa Shin-zan was made a Special Natural Treasure by the government.
Nevertheless, Mimatsu never turned away tourists – but nor did he charge them admission, a practice still upheld. The Mimatsu Masao Memorial Hall (三松正夫記念館), tucked behind the ghastly row of giftshops at the base of the volcano, contains an interesting collection of exhibits on the history of the fledgling volcano.