“Hundreds of tons of unexploded bombs from the war remain buried around Japan and are sometimes dug up at construction sites.”
A 500-pound US bomb sat under a Miyazaki Airport taxiway for about 80 years and then went off on its own. It left a crater 7 meters wide and cancelled more than 80 flights. Nobody knows what set it off. Miyazaki was a kamikaze training field, and bombs dropped on it keep turning up. Aircraft taxi over that ground every day.