MOUNT MANTAP, NORTH KOREA — Chinese experts say the North's main nuclear test site has collapsed, which may be why Pyongyang suspended missile tests.
The South China Sea Morning Post reports that North Korea's last six nuclear tests were all carried out at the Punggye-ri testing facility under Mount Mantap.
During the latest test in September 2017, a bomb believed to have an explosive yield of 100 kilotonnes set off a powerful explosion. It caused an initial 6.3 magnitude tremor, and triggered several more earthquakes in the weeks that followed.
Geologists from the University of Science and Technology of China analyzed the region's seismic data and found that the blast vaporized surrounding rock, creating a 200-meter hole as the area collapsed in on itself.
A large section of the mountain ridge near the peak is also believed to have broken off as a result of shock waves.
Researchers from the Jilin Earthquake agency reported similar findings, and added that the collapse created a chimney which could leak radioactive fallout into the air.
Both studies concluded the testing site to be unstable and unusable.
The area is located close to the Chinese border. But while authorities say no increase in radioactivity levels have been detected, they will continue monitoring the surrounding region.