[SCMP] The collapse after five nuclear blasts may be why North Korean leader Kim Jong-un declared on Friday that he would freeze the hermit state's nuclear and missile tests and shut down the site, one researcher said. The last five of Pyongyang's six nuclear tests have all been carried out under Mount Mantap at the Punggye-ri nuclear test site in North Korea's northwest.
One group of researchers found that the most recent blast tore open a hole in the mountain, which then collapsed upon itself. A second group concluded that the breakdown created a "chimney" that could allow radioactive fallout from the blast zone below to rise into the air.
A research team led by Wen Lianxing, a geologist with the University of Science and Technology of China in Hefei, concluded that the collapse occurred following the detonation last autumn of North Korea's most powerful thermal nuclear warhead in a tunnel about 700 metres (2,296 feet) below the mountain's peak.
The test turned the mountain into fragile fragments, the researchers found