A massive concrete dome containing tens of thousands of tons of radioactive waste is deteriorating in the Pacific Ocean, raising serious long-term safety concerns.
Known as the Runit Dome (or simply “The Tomb”), the structure was built by the United States between 1977 and 1980 on Runit Island in the Marshall Islands. It entombs more than 120,000 tons of radioactive soil, debris, and contaminated material from decades of U.S. nuclear weapons testing in the region.
The waste is buried inside a crater left by the 18-kiloton “Cactus” nuclear test detonated in 1958. Some of the nuclear explosions conducted across the Marshall Islands were reportedly up to 1,000 times more powerful than the bombs dropped on Hiroshima and Nagasaki.
Originally designed as a temporary solution, the dome was never meant to last indefinitely. Today, cracks have appeared in the concrete, and seawater is already seeping into the underlying crater through the porous coral foundation. While current leakage levels remain relatively low, scientists are growing increasingly worried about the future.
Runit Island sits just 6.5 feet (2 meters) above sea level. With climate change driving sea level rise, projected to reach roughly 3 feet (1 meter) by 2100 in the region, the risks of flooding, storm surges, and accelerated erosion are rising. Experts warn that a major storm or further structural failure could spread radioactive contaminants into the surrounding lagoon and broader marine environment.
Among the most concerning materials inside is plutonium-239, which remains dangerously radioactive for over 24,000 years.
For the people of the Marshall Islands, the crumbling dome has become a powerful symbol of both the nuclear legacy left by decades of testing and the new threats posed by a changing climate. What was meant to be a short-term fix now faces an uncertain and potentially hazardous future.