Excavation of the Colossal Cavern for Hyper-Kamiokande Completed
On July 31, 2025, a major milestone was achieved for the Hyper-Kamiokande project by completing excavation of one of the world’s largest underground rock caverns. Located 600 meters beneath a mountain in Gifu Prefecture, the cavern will house an ultra-large water Cherenkov detector with a fiducial volume 8.4 times larger than its predecessor, Super-Kamiokande. The international collaboration includes around 630 researchers from 22 countries including Canada. The cavern’s dome section, 69 meters in diameter and 21 meters high, and its 73-meter-tall cylindrical section were excavated through complex geological conditions, requiring advanced stabilization methods, real-time monitoring, and efficient waste rock removal via a vertical shaft. Excavation, totaling about 330,000 cubic meters of rock, finished approximately six months behind schedule due to reinforcement needs. With excavation completed, work will now begin to construct the 260,000-cubic-meter water tank, followed by installation of over 20,000 new photodetectors and other components between 2026 and 2027. The Canadian group, led by UVic/VISPA members, Hartz, Karlen, and Konaka, are building multiPMT modules for the experiment. The Hyper-K detector is scheduled to be operational in 2028, marking a significant step toward solving fundamental questions about the universe.
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