Since 1958, tidal groundwater has continued moving beneath Runit Dome in the Marshall Islands, where 85,000 cubic meters of radioactive material rest; now rising Pacific seas are raising questions about the future of the 115-meter-wide structure

Tidal groundwater moves freely beneath Runit Dome in the Marshall Islands. Built over a nuclear crater, the 115-meter concrete structure holds 85,000 cubic meters of radioactive waste. Now, rising Pacific sea levels raise severe environmental concerns about its future. Water continuously flows through its porous limestone base into the lagoon. Local leaders worry rising ocean tides could soon trigger a major nuclear catastrophe.