Mount Iō (硫黄山, Iō-zan) also Mount Iwo is an active andesitic stratovolcano on the Shiretoko Peninsula of Hokkaidō, Japan.

[3] Mount Iō literally means, sulphur mountain.

There are two explosion craters and a lava dome at the summit of the volcano.

[4] Volcanic activity started at least 240,000 years ago.

[4] Mount Iō has erupted at the following times:[5]