Formed by Mt. Hiyori’s eruption, Oyunuma Pond is located within the same general vicinity of both Jigokudani and Noboribetsu Onsen. The pond has roughly a one-kilometer circumference and a max depth of twenty-two meters. This pond is to have once been a majestic geyser but due to the over-extraction of sulfur during the Meiji period it turned into its current shape. The pond offers visitors an impressive display of volcanic activity.