Hokkaido Official Tourism Site HOKKAIDO LOVE!

Mt. Io, an active volcano that is the source of Kawayu Onsen. You can observe white smoke rising from countless fumaroles up close and experience the powerful sensation of being enveloped in the smell of sulfur.
Mt. Io, called Atosanupuri meaning "naked mountain" in Ainu language, is an active volcano that is the source of Kawayu Onsen. Once prosperous with sulfur mining, plants hardly grow on the brown, desolate mountain slopes, and white smoke containing sulfur vigorously rises from countless fumaroles. You can approach very close to the fumaroles, the sound of steam spouting from the ground echoes, and the strong smell of sulfur pervades the area.
Around the fumaroles, when you bring your hand close to the ground warmed by geothermal heat, you feel heat, and rising steam flows in the wind and touches your skin. Yellow sulfur crystals underfoot cover the rock surface, and you can witness the vitality of the volcano with your own eyes. At the foot of the mountain, a large colony of "Ezo Isotsutsuji," endemic to Hokkaido, spreads, and from June to July every year, pure white small flowers bloom all at once. From the town of Kawayu Onsen to Mt. Io, "Tsutsugahara Nature Exploration Path" is maintained, guided tours are also conducted, and you can stroll while learning about the geology and vegetation of the volcano.