Some press reports have suggested the possibility that a World War II sea mine may have been responsible for the explosions that caused the Russian nuclear submarine Kursk to sink in the Barents Sea. Can a 50-year-old sea mine really still go off? And how are sea mines different from land mines?
A WWII-era sea mine could definitely explode. Mines used in more recent wars are often set to deactivate, with clocks that can either interrupt the firing circuit or detonate the mine, but older models have no such "off" switch. More than 550,000 sea mines were laid during World War II; they could be set off by contact, or by sensing the magnetic change caused by a passing ship or submarine. It's impossible to know how many latent mines are still in the ocean--after the war, the major powers tried to remove them all, but it's very likely that some were missed (and some countries, such as Iran, Iraq, and North Korea, still use the older models). Russian military officials have said that several were recently found in the area near the Kursk.
Sea mines are larger and much more expensive than land mines. Anti-personnel land mines can have as little as 3 pounds of explosives and can cost as little as $3, while sea mines typically carry 500 pounds of explosives and even a low-technology moored mine costs around $1,500.
(Explainer has already discussed why the Russian submariners couldn't have swum to the surface.)
Explainer thanks Lee Hunt of the Mine Warfare Association and Samuel Loring Morison, a naval analyst and editor of The International Guide to Naval Mine Warfare.