North Korean president Kim Jong-un recently announced his country has halted its nuclear testing program. While it is unclear whether this is a political move in preparation for meeting with the United States president Donald Trump, recent evidence suggests the country may have been forced to halt testing.

A recent study by a group of geologists discovered that the mountain used by North Korea for its nuclear bomb testing has collapsed as a result of the explosions. The collapsed mountain is raising concerns about radioactive fallout, which could make its way into China.

Scientists from the University of Science and Technology of China believe this could be the true reason North Korean President Kim Jong-un announced the halt of their nuclear testing program.

The collapse of Mount Mantap was a result of five recent nuclear blasts at the Punggye-ri nuclear test site in northwest North Korea. The recent nuclear tests tore open a hole in the mountain, causing it to collapse and creating a pathway for radioactivity to escape from the mountain.

The team of Chinese geologists believes the collapse was a result of the detonation of North Korea’s most powerful nuclear warhead last fall. The nuclear bomb was detonated about 2,300 feet beneath the mountain’s peak, causing aftershock earthquakes and collapse of the mountain.

The research, which will be published next month in the peer-reviewed journal Geophysical Research Letters, examines satellite imagery before and after the nuclear tests. There is ongoing concern that the collapse ejected radioactive dust, which could make its way into China and other neighboring countries.

The first four underground nuclear tests last year did not produce visible structural damage to the mountain as detected through satellite imagery. However, the 5th nuclear test, a 100-kilotonne nuclear bomb that was detonated on September 3rd caused significant structural damage to the mountain.

The bomb likely vaporized the surrounding rock and blew a hole in the side of the mountain according to Wen Lianxing, the lead geologists on the project from the State University of New York at Stony Brook. After analyzing satellite imagery and the response from seismic stations, the research team concluded that the blast caused a large section of the mountain to collapse on itself.

The United States Geological Survey reported a magnitude 6.3 earthquake, followed by a second 4.6 magnitude earthquake shortly afterward coinciding with the detonation of the September nuclear test.

Evidence of the collapse of Mount Mantap suggests it could be the underlying cause of North Korea halting its nuclear tests. Time will show whether the recluse country will develop a new nuclear test site or whether this marks the end of nuclear testing by North Korea.