Mt. Sanbe’s Hot Springs

Sanbe Onsen is the only hot spring in the western Honshu heated by high-temperature magma emanating from an active volcano.
The source of the hot spring wells up in a gorge (Okunoyu explosion crater) between Mt. Magosanbe and Mt. Hikage. The spring temperature is between 39 to 41 degrees Celsius, and 360 liters of hot water are emitted per minute. Swampland in the vicinity of the spring source and other land nearby have iron deposits and are of a rusty hue.

Mt. Sanbe spring source

Hot springs in the western Honshu can be largely classified as either volcanic or non-volcanic in origin. Among the hot springs in the region, Sanbe Onsen is the only volcanic hot spring. Beneath the volcano, at a depth of several kilometers to 10 kilometers, is a place where magma rises from the depths and creates magma pools. Here, the temperature is more than 1,000 degrees Celsius.
At the non-volcanic hot springs, on the other hand, groundwater is heated to the ground temperature, turns into a hot spring and gushes out. In the western Honshu, many hot springs including Misasa Hot Spring (Tottori Prefecture) and Tamatsukuri Hot Spring (Shimane Prefecture) are radioactive hot springs. This is closely connected with the widespread presence of granite in the region.

Origin model for hot springs in the San’in Area