Mt. Io (Atosa-nupuri)(硫黄山)

  • Mt.Io

Mt. Io (Sulfur Mountain) is called Atosa-nupuri (Bare Mountain) in the Ainu language because of its barren, rocky face. Mt. Io is a 508m volcano that was formed sometime between 500 and 2,000 years ago. Hot steam escapes from the earth through 1,500 “fumaroles” (small vents) of various sizes. The air is heavy with the distinct odor of sulfur, and the bright yellow vents create an otherworldly sight. Volcanic gases have affected vegetation in the surrounding area, easily seen by looking at the neighboring peak of Mt. Kabuto: stark differences in plant life are visible between the side facing Mt. Io and the side facing away. Kawayu Onsen’s hot springs originate from Mt. Io’s geothermal activity.

History of Mining on Mt. Io

The sulfur in Mt. Io has long been used for goods such as dyes and matches. In 1877, a sulfur mine was dug into Mt. Io.The uses of sulfur expanded to include not only the making of matches, but also gunpowder, insecticides, and paper, and even producing electricity. Mt. Io’s sulfur was exported abroad to several countries, including Qing Dynasty China and the USA, and sulfur production became an important industry for the area surrounding Teshikaga Town, including Kawayu Onsen. In 1887, Hokkaido’s second railway lineopened on Mt. Io, replacing the use of horses to transport the mined sulfur. Eventually, demand for sulfur decreased and the mine was permanently closed in 1963.

Hiking Trails around Mt. Io

The Tsutsujigahara Nature Trail is a trail at the foot of Mt. Io, taking approximately 60 minutes to reach Mt. Io’s slopes from the Kawayu Eco-museum Center. Along the way, the vegetation changes dramatically due to increasing soil acidity. The trail winds through a lush forest of Sakhalin spruce and into a forest of Japanese oak before opening onto lowlands covered in Japanese stone pine and marsh Labrador tea. In June, the fields of Labrador tea burst into a beautiful carpet of white flowers. Other trails in the area include the Sakhalin Spruce Forest Trail, which consists of a short trail (30 minutes) and a long trail (60 minutes), and the Aoba Tunnel Trail, an approximately 30-minute hike from JR Kawayu Onsen Station to the foot of Mt. Io.


This is an active volcanic zone. Steam emitted from openings in the earth’s crust reaches temperatures over 100°C.
For your safety, DO NOT climb over the fence.


  1. Yunokaku Bekkan Yumoto Ikedaya Hotel(湯の閣 別館 湯元 池田屋)

  2. Gensen Festival at Kawayu Hot Springs (August)(湯のまち川湯 源泉まつり)

  3. Kawayu Onsen Guest House NOMY(川湯温泉ゲストハウスNOMY)

  4. Diamond Dust in Kawayu(ダイヤモンドダスト in KAWAYU)

  5. Kawayu Onsen Tourist Information Center(川湯温泉観光案内所)

  6. Cafe NOBLE(café NOBLE)

Teshikaga Live Camera