97.4m Depth Record: Japanese Diver Reaches Bottom of Oita's Inazumi Underwater Cave, Reveals 300-Million-Year-Old Geology
At Inazumi Underwater Cave in Oita Prefecture, professional diver Yuji Ohama (60) and his team reached 97.4m depth on March 20, 2026, likely a Japanese national record for underwater limestone caves. Formed 300 million years ago and submerged by an Aso volcanic eruption 85,000 years ago, the cave's deepest section revealed primordial stalactites and geological strata never seen above ground. We compare this discovery with Mexico's cenotes and Florida's cave systems, and explore Japan's only commercially diveable underwater limestone cave.