Obuki Spring was added to Your Favorites!
Towada-Hachimantai NP, Akita
Claim this place to tell your story your way.
About 9,000 liters of hot spring water gush from Obuki every minute—the largest flow from a single hot-spring outlet in Japan. It gathers into a steaming stream about 3 meters wide.
Hokutolite’s name points to Taiwan’s Beitou, not Akita: the mineral was collected at Tamagawa in 1898, then matched to Beitou’s in 1911. The spring’s water helped reveal this surprising connection.
Obuki’s water emerges at about 98°C and around pH 1.1–1.2. Its striking acidity is linked mainly to hydrochloric acid from volcanic gases—a distinctive chemistry for a hot spring.
As Obuki’s water cools downstream in the Yugawa, minerals form a Hokutolite crust on riverbed stones. It grows only about 1 millimeter per decade, and the deposit is protected as a Special Natural Monument.
Obuki’s acidic outflow contributed to the Tamagawa water diverted into Lake Tazawa from 1940. The lake acidified and its native kunimasu disappeared; the fish was rediscovered in Lake Saiko in 2010.
Researchers infer that Obuki’s water carries volcanic gas from deep underground alongside rain-derived water. Isotope-based studies estimated a volcanic-gas-to-rainwater mixing ratio of about 1:5.
From 1841, the Akita lord ordered drainage work by Kakunodate samurai Taguchi Kōemon, his son and retainer Hiraka Tōgorō. They channeled rain away, believing seepage underground caused the spring’s acidity.
Downstream, Obuki’s water flows through limestone treatment tanks using natural gravity. The system uses about 40 tonnes of limestone a day; the rock dissolves as it reduces the water’s acidity.
Near Obuki, ganban-yoku turns geothermal-heated ground into a place to rest: visitors spread straw mats on warm rock and cover themselves with blankets. Some patches reach 40–50°C.
Tamagawa’s hot spring was discovered in 1681. It opened as a center for toji—hot-spring convalescence—in 1884, then grew into a major hot-spring resort after 1932.
