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Noboribetsu-Oyunuma Pond

Noboribetsu-Onsen village, Noboribetsu city, Iburi branch, Hokkaido, Japan

"No Trespassing" signs on the lake shore

Synonym

Noboribetsu Mine

Occurrence

Fumarole deposit

Sulphur melt lying on the bottom of the Oyunuma Crater Lake formed at the the Oyunuma Explosion Crater of the Kuttara Volcanic Group which has been active since Late Pleistocene (80 ka). The Oyunuma Explosion Crater was formed in the Noboribetsu Stage after Late Pleistocene (40 ka). The Oyunuma Crater Lake is at the south of the early Holocene (10 ka) Hiyoriyama Lava Dome. The Hiyoriyama Lava Dome is composed of dacite and is still active. Explosion craters of the Kuttara Volcanic Group are active and the latest phreatic explosion was 200 years ago.

Noboribetsu-Oyunuma Pond

A crater lake, Oyunuma, of the Oyunuma Explosion Crater. Sulphur melt lying on the bottom of the crater lake. Hollow spherules of sulphur was formed from the melted sulphur at the bottom of the crater lake. Volcanic gas bubbles lifted sulphur melt to the pond water, and sulphur melt was cooled imprinting the shape of bubbles. These spherules are floating on the lake water. Sulphur recovered from this lake looks black as it contains plenty of fine sulfide grains such as pyrite. The black mud at the lake shore in this photograph is broken sulphur spherules. There are some fumaroles emitting volcanic gas in this photograph. The pale brown cliff over the lake is composed of grayish-white dacite to rhyolite,

Reported Minerals

Localities

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