Arayu Fumaroles
Openings in the ground called fumaroles are created when superheated water from deep in the earth emerges at the surface as water vapor and steam. The sulfur-laced vapor rising from the fumaroles dotting the hillside at Arayu is the last reminder of the volcanic activity that created Shiobara’s topography and hot springs. The sulfur in the steam gives the area its distinctive pungent odor and is also responsible for the weathered and chalky appearance of nearby rocks. Most of the hot springs in Arayu Onsen originate here; their characteristic milky white color comes from the natural infusion of sulfuric gas into the hot-spring water.