Lewis, of the Middlebury Institute, argues that the tunnel's horizontal layout would also make it relatively easy to "pop" open the sealed entrances and regain access after their closing. The authors speculate that may be because they'll be blown up in front of members of the worldwide media later this month. "If North Korea has really made a decision to denuclearize, it has no reason not to invite them".
Kim's regime said through state-run news agency KCNA that ongoing "Max Thunder" joint military exercises between the United States and South Korea are actually a "rehearsal for invasion" of the North.
The country also vowed to stop testing missiles without notifying the global community Saturday.
The Americans welcomed the North Korean announcement.
An ex-North Korean official suggested that his former country may have a different definition of the term that has been circulating around foreign policy circles ahead of the upcoming summit between US President Donald Trump and North Korean leader Kim Jong Un: denuclearization.
While both the US and South Korea welcomed the move, Japan struck a discordant note.
Siegfried Hecker, a former director of the Los Alamos National Laboratory in the United States and a leading expert on North Korea's nuclear programme, said collapsing the Punggye-ri tunnels would be "a big and positive step", given his belief that North Korea still required more nuclear and missile tests to reach the USA mainland with a nuclear-tipped missile.
Facebook reports spike in violent content
Facebook says 0.22-0.27% of views by users were of content that violated its standards around graphic violence in the period. This, the company says, is because there is little of it in the first place and because most is removed before it is seen.
The 38 North report confirmed an earlier analysis from a team of researchers at the James Martin Center for Nonproliferation Studies who determined that North Korea was tearing down buildings near the nuclear test site. They speculated that Pyongyang may be trying to remove sensitive information form the site.
Some in the worldwide community believe Kim's commitment to close Punggye-ri is a welcome development.
Investment in North Korea could benefit everyone if executed wisely, and of course South Korea needs to help the North build up its decrepit infrastructure in order to prepare for reunification. The latest test in September previous year, which was also the largest and saw a hydrogen bomb being exploded, triggered an natural disaster of 4.1 magnitude after a cavity collapsed under the mountain, causing damage to the test-site, according to the findings of two Chinese seismological research groups. And, of course, tests don't need to be underground.
Possibly not. Both India and Pakistan established themselves as nuclear powers after a similar number of tests - and neither has detonated a bomb since 1998.
'DPRK will join global desires and efforts for a total ban on nuclear tests, ' Han Tae-song said in an address to the Conference on Disarmament, using North Korea's official acronym.
38 North observed late a year ago what it described as "significant tunneling operations" at a portal that has yet to be used.