Another test might cause the whole mountain to cave in on itself, leaving only a hole from which radiation could escape and drift across the region, including China, he said.
“We call it ‘taking the roof off’. If the mountain collapses and the hole is exposed, it will let out many bad things.”
Sunday’s blast was followed by an earthquake eight minutes later, which China’s seismic authorities interpreted as a cave-in triggered by the explosion.
Not every mountain was suitable for nuclear bomb testing. Wang said, adding that the peak had to be high, but the slopes relatively flat.
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Based on the fact that North Korea has a limited land area and bearing in mind the sensitivity of its nuclear program, it most likely does not have too many suitable peaks to choose from.
How long the mountain would continue to stand would also depend on where the North Koreans placed the bombs, Wang said.
“If the bombs were planted at the bottom of vertically drilled tunnels, the explosion would do less damage,” he said.
But vertical tunnels were difficult and expensive to build, and it was not easy to lay cables and sensors to collect data from the explosion, he said. Much easier was to bore a horizontal tunnel into the heart of the mountain, but this increased the risk of blowing off the top, he said.
