N.Korea's Nuclear Test Mountain 'Sinks Half a Meter'

The mountain above the North Korean nuclear test site in Punggye-ri has subsided by half a meter since last year, according to a group of international scientists.

The group of scientists from China, Germany, Singapore and the U.S. published a report in the latest edition of Science after analyzing satellite images of Mt. Mantap before and after North Korea's nuclear test on Sept. 3 last year.

They show the entire mountain rising 2 m due to the shock of the blast and then collapsing 0.5 m afterwards. 

The researchers analyzed synthetic-aperture radar (SAR) images of Mt. Mantap taken by German and Japanese satellites. SAR calculates the distance from the satellite to the surface of the earth to determine changes in altitude.

The scientists believe the nuclear blast occurred around 450 m below the peak of Mt. Mantap, which stands 2,205 m above sea level. The blast melted the surrounding granite, creating a cavernous hollow measuring around 50 m in diameter.

Douglas Dreger of U.C. Berkeley, and one of the authors, said the collapse of Mt. Mantap appears to be continuing.

The scientists said the underground tunnel beneath Mt. Mantap may have collapsed after the sixth nuclear test caused an artificial earthquake measuring 5.2 on the Richter scale followed by a 4.5-magnitude aftershock some minutes later.

They believe the aftershock in fact originated from a point 700 m south of the blast site, which stands between it and the entrance of the shaft and appears to have been caused by the collapse of either an underground tunnel or another hollow that was formed by a previous nuclear test.

Based on the data, the researchers estimated the North's sixth nuclear test at 120 kilotons (equivalent to 120,000 tons of TNT), which would make it eight times stronger than the atomic bomb that was dropped on Hiroshima, Japan at the end of World War II.

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