New research, published this week in the journal Science, supports prior speculation that North Korea’s September nuclear test last year could have led to a collapse of the mountain in which the test site has hidden. The study, which was detailed Thursday in a report from Live Science, shows movement and compression, if not a full collapse.
The test was conducted at Punggye-ri on September 3rd, and marked the nation’s largest nuclear test to date, registering as equivalent to a 6.3 magnitude earthquake. A smaller, 4.1-magnitude event, 8 minutes later and 700 meters to the south, led geologists to wonder if the test may have caused a collapse of the mountain.
This could have partially or entirely buried the test facility. Such a scenario would prevent further nuclear testing at the site and would heighten the risk of radioactive gas leaking into the air and surrounding area.
Three weeks ago, North Korea said it was closing the site at Mount Mantap, and geologists in China published a study in April suggesting a collapse of the mountaintop, in the journal Geophysical Research Letters.
In the past, most efforts to assess these explosions have focused on seismic data. This time, scientists have used satellite imagery to compare the site before and after the nuclear test, using a synthetic aperture radar. This technique sends electromagnetic waves to earth, and measures the reflected light. This allows scientists to gain high-resolution imagery, even during bad weather and low light conditions.
According to the paper’s first author, Earth Observatory of Singapore senior research fellow Teng Wang, the results suggested a collapse of the tunnels within the mountain test site. The images showed that the mountain had shifted 3.5 meters and shrank 0.5 meters.
But without on-site investigations, Wang explained “we could not tell if this is the collapse of the whole test site or the collapse of the tunnel, as there is no direct evidence for it.”
The researchers also examined seismic data, and discovered that the waves from the second tremor travelled in the opposite direction of those from the nuclear blast, supporting the idea of a collapse in the wake of an explosion.
Some scientists cautioned against drawing conclusions without first-hand reports. University of California earth and planetary scientist Douglas Dreger notes, “It’s really hard to make that judgment call without having information at that site — getting boots on the ground and investigating it.”
He suggested that the tremors could have been the result of a smaller collapse of a gap in the rocks created by a previous explosion, or the collapse of a single tunnel or set of tunnels.
“I wouldn’t say that the whole mountain collapsed, I wouldn’t draw the catastrophic conclusion,” said Dreger.