1. It was solid rocket fuel, from a cargo of missiles.
2. It was a collision, accidental, "fertilizer" etc.
3. We or a friendly intel agency blew up whatever was on the carriage (planted bomb e.g.)
4. Sub critical event from too much U-235 items getting too close to each other. (Uncontained, it blows apart the material and halts a chain reaction that way).
From previous reports, some important facts -
- "The station was destroyed as if hit by a bombardment and debris flew high into the sky," Yonhap said, quoting the unidentified Chinese sources."
- "North Korea appears to have cut international telephone lines to the area to prevent information about the explosion getting out, Yonhap added. The North appears to have declared a type of emergency in the area.
- The blast reportedly damaged structures up to 2 km away, other estimates say 1.5km. Most structures within 500 meters were leveled, including some apparently of brick or cinderblock. Some reports of debris up to 10 miles away. And there are conflicting reports of possible casualties up to 5 miles away. Reports of the depth of the crater say up to 15 meters deep.
- Initial media reports on the cause of the crash were clearly made up stories. The story has changed to explosion of stuff carried on some of the cars of one train. Satellite pictures of the craters show two distinguishable longish areas generally following the axis of the rail line.
My best guess is they were transporting missiles which blew up. But other causes can't be ruled out IMO.
The craters you refer to do not follow the axis of the rail line, they are perpendicular to the rail lines. Furthermore, the "two" craters, and their oblong shape are due to tractor excavation and fill in. That's already been covered and documented on this thread.
Nor is it likely that the explosion was due to either rockets or bombs due to the lack of fragmentation or rocket engine/body debris. There are copious documentary photos of the blast area to attest to this. See thread for photos and links to photos.
The "ammonium nitrate" story is also highly unlikely. See this link for detailed explanation as to why that is.
--Boot Hill