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Towada-Hachimantai NP, Akita
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At Yakeyama’s western foot, Tamagawa Onsen’s Ōbuke spring gushes about 9,000 L a minute at 98°C and pH 1.2. Its startling acidity comes mainly from hydrochloric acid, not sulfuric acid.
On 11 May 1997, a landslide at Sumikawa Onsen on Yakeyama’s northeast flank triggered a steam explosion. It destroyed the hot-spring buildings, then swept down-valley as a debris flow for about 1.4 km.
In 1940, acidic Tamagawa water from Yakeyama’s western foot was diverted into Lake Tazawa for power and irrigation; the lake’s native kunimasu disappeared. Thought extinct, the fish was rediscovered in Lake Saiko in 2010.
Tamagawa’s hot water deposits hokutolite, a rare barium-lead mineral with striped layers. First found here in 1898, it was named after Taiwan’s Beitou springs; the Tamagawa deposit is a Special Natural Monument.
Long before modern treatment, acidic runoff was called Tamagawa’s “poison water.” From 1841 to 1852, the Akita domain ordered a control project led by Kakunodate retainer Taguchi Kōemon, his son, and aide Hiraka Tōgorō.
A newspaper account says the 6 July 1887 blast at Soranuma scattered ejecta 1 km and opened a crater 36 m wide—and a hot spring began flowing there. This eruption literally made a new spring.
On 16 August 1997, a steam blast at Soranuma occurred near the 1949 crater group. That earlier eruption opened 3 vents just 5–15 m wide; its southern vent erupted again in 1951.
Yakeyama’s 1,366 m summit sits on the southwest rim of a 600 m crater, not in its center. The middle holds Onigajo, a rugged lava dome whose name means “Demon’s Castle.”
Life returns to Yakeyama’s acidic crater slopes in a sequence: wavy hair-grass first forms rings, sedges follow on gentler ground, and shrubs fill in later. Late-melting snow supports dense pink iwa-kagami.
At Mōsen Pass, mats of crowberry and lingonberry make the slope look as if someone laid down a red carpet. The vivid “rug” is made by low-growing wild plants, not a human-made trail feature.
A local discovery tale places Tamagawa’s first hot spring in 1680, found by a hunter. It later became known as “Deer Springs” after a wounded deer was reportedly seen soaking in its warm water.
At Tamagawa, ground heat warms the stone used for ganbanyoku: visitors lay a mat on the warm rock and rest under a blanket. It is a bathing custom that turns the volcano’s natural heat into a floor warmer.
