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North Korea’s Nuclear Tests Could Be Changing the Country’s Geology

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The North Korean mountain used for the underground testing of nuclear weapons might be suffering from “tired mountain syndrome,” according to experts studying satellite photos of the test site.

Tired mountain syndrome” is the name for increased fractures and permeability in the surrounding rock, caused by multiple underground nuclear tests. Mount Mantap is a 7,200-foot-high peak in the north of the country, which scientists say “visibly shifted” during North Korea’s most recent detonation on Sept. 3.

During that test, an 85-acre area on the mountain was observed to visibly subside, and landslides were reported shortly after. Three small earthquakes have been detected near the Punggye-ri test site since the last test, in an area not known for seismic activity.

But experts Frank Pabian and Jack Liu said there is no reason to believe the site is unable to take future testing. Writing in a specialist publication that monitors North Korea, they said this was based on the precedent set by U.S. underground testing, and the fact that the mountain still has two unused tunnel complexes that could host tests.

The most recent detonation was the most powerful so far; analysts say it was at least 17 times as powerful as the bomb the U.S. dropped on Hiroshima in 1945.

North Korea has conducted six nuclear tests, five of which have been at the mountain. Tensions between North Korea and the U.S. are at their highest point in years, after the September test and missile launches over Japan. The isolated country is seen as drawing ever-closer to being able to mount a nuclear weapon on an intercontinental ballistic missile that could reach the U.S. mainland.

In a Sepember address to the United Nations shortly after the test, President Donald Trump vowed to “totally destroy” North Korea if it did not halt its nuclear weapons program.

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Write to Billy Perrigo at billy.perrigo@time.com