North Korea's 2017 Nuclear Explosion Was Equivalent of 17 Hiroshima Bombs, Study Suggests

The nucler weapon detonated underground by North Korea in 2017 could have been 17 times as powerful as the "Little Boy" bomb dropped on the Japanese city of Hiroshima in 1945.

According to research recently published in the Geophysical Journal International, the North Korean blast released energy equivalent to 245 and 271 kilotons of TNT. In contrast, the "Little Boy" bomb that the U.S. deployed over Hiroshima contained a blast yield of 15 kilotons.

North Korea Interballistic Missile
This picture from North Korea's official Korean Central News Agency (KCNA) taken on August 29, 2017 and released on August 30, 2017 shows North Korea's intermediate-range strategic ballistic rocket Hwasong-12 lifting off from the launching pad at an undisclosed location near Pyongyang, shortly before the detonation of a hydrogen bomb in an underground chamber on September 3, 2017. STR/AFP/Getty

North Korea kick-started its nuclear program after withdrawing from the Treaty on the Non-Proliferation of Nuclear Weapons in 2003. The first of a series of nuclear tests took place three years later, in 2006, and culminated in the testing of what experts suspect was a hydrogen bomb on September 3, 2017.

While most nuclear tests are measured using the same networks used to monitor earthquakes, there are no stations openly releasing seismic data near the test site used by North Korea in 2017. This makes it extremely hard to determine the location and calculate the size of the bomb.

As Newsweek reported at the time, everyone outside of the North Korean regime had to make an educated guess as to the size of the explosion—and these varied substantially.

U.S. intelligence estimated an explosive power equivalent to 140 kilotons of TNT, The Diplomat reported. Elsewhere, the estimation was as low as 50 kilotons and as high as 500 kilotons.

The actual figure, according to researchers at the Space Applications Centre of the Indian Space Research Organisation (ISRO), is somewhere in the middle—and significantly higher than those put forward by U.S. intelligence.

The team was able to work out the explosive power of the 2017 test using satellite data.

"Satellite based radars are very powerful tools to gauge changes in earth surface, and allow us to estimate the location and yield of underground nuclear tests," said K. M. Sreejith of the Space Applications Centre, lead author of the study, in a statement. "In conventional seismology by contrast, the estimations are indirect and depend on the availability of seismic monitoring stations."

Sreejith and colleagues used a technique called Synthetic Aperture Radar Interferometry (InSAR), which produces maps of surface deformation from radar images collected in space. This process enables scientists to track changes in land deformation over time and in this case, land changes directly above an underground test chamber in Mount Mantap, northeast North Korea, where the bomb was tested in 2017.

From these maps, Sreejith and colleagues concluded the 2017 explosion generated enough power to move parts of the mountain above the point of detonation by a few meters. The study's authors were also able to determine the location of the explosion—540 meters or so below the summit and around 1.5 miles to the north of the entrance of the tunnel leading to the test chamber.

Hiroshima 1945
HIroshima, after the atomic bomb was dropped. According to the Asian American Studies Center at UCLA, 150,000 people were killed or injured by the nuclear explosion—but this is considered to be a conservative estimate. Keystone/Getty

In 2017, Newsweek determined the number of casualties of 15-kiloton and 150-kiloton bombs were they to hit Newsweek's New York office—174,640 deaths and 477,470 deaths, respectively—using Alex Wellerstein's NukeMap. Wellerstein is a science historian at the Stevens Institute of Technology with a specialty in nuclear weapons.

Were a 271-kiloton bomb to hit New York City and land in lower Manhattan, it would cause close to a million deaths.

The Statista graph below shows North Korea's nuclear infrastructure as of March 2019.

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North Korea's nuclear infrastructure. Statista