|The cloud rose well above the horizon|
Fukushima Diary reports of this strange and worrying incident on which no official details have been produced as of now.
The explosion, which must have been huge and possibly nuclear, happened on Wednesday's morning, while the US Air Force was having a military drill 28 Km North of Kumejima, East of Okinawa. No details have been officially reported.
While not all mushroom-shaped clouds need to have been caused by nuclear weapons, they need to be caused by really huge explosions, and the easiest way to get one of those is nuclear, of course.
The residents of Kumejima felt the ground shaken and the sound of the explosion. To cause that kind of effects at 28 km of distance it must have been something really big. And that again brings us to the likelihood of a nuclear weapon or reactor being involved.