The short answer is that it’s too early to tell. The longer answer is, in the words of Ronald Reagan, “trust, but verify.” Not that North Korea is actually deserving of trust.

Last Friday, collective jaws dropped around the world when Kim Jong-Un crossed into the DMZ and shook South Korean President Moon Jae-in’s hand, and then the two sat down to formally pledge an end to the Korean War – a war that technically was still in progress because a ceasefire, not a peace treaty, was enacted in 1953.

So, what brought this about? Perhaps the analysis by Chinese scientists that Kim had basically blown up his own underground testing site – the one that he has now pledged to close – which meant that any more nuclear testing might set off a volcano.

A research team led by Wen Lianxing, a geologist with the University of Science and Technology of China in Hefei, concluded that the collapse occurred following the detonation last autumn of North Korea’s most powerful thermal nuclear warhead in a tunnel about 700 metres (2,296 feet) below the mountain’s peak.

The test turned the mountain into fragile fragments, the researchers found.

The mountain’s surface had shown no visible damage after four underground nuclear tests before 2017.

But the 100-kilotonne bomb that went off on September 3 vaporised surrounding rocks with unprecedented heat and opened a space that was up to 200 metres (656 feet) in diameter, according to a statement posted on the Wen team’s website on Monday.

As shock waves tore through and loosened more rocks, a large section of the mountain’s ridge, less than half a kilometre (0.3 mile) from the peak, slipped down into the empty pocket created by the blast, leaving a scar visible in satellite images.

Wen concluded that the mountain had collapsed after analysing data collected from nearly 2,000 seismic stations.

Three small earthquakes that hit nearby regions in the wake of the collapse added credence to his conclusion, suggesting the test site had lost its geological stability.

Another research team led by Liu Junqing at the Jilin Earthquake Agency with the China Earthquake Administration in Changchun reached similar conclusions to the Wen team.

The “rock collapse … was for the first time documented in North Korea’s test site,” Liu’s team wrote in a paper published last month in Geophysical Research Letters.

The breakdown not only took off part of the mountain’s summit but also created a “chimney” that could allow fallout to rise from the blast centre into the air, they said.

Zhao Lianfeng, a researcher with the Institute of Earth Science at the Chinese Academy of Sciences in Beijing, said the two studies supported a consensus among scientists that “the site was wrecked” beyond repair.

“Their findings are in agreement to our observations,” he said.

“Different teams using different data have come up with similar conclusions,” Zhao said. “The only difference was in some technical details. This is the best guess that can be made by the world outside.”

Speculation grew that North Korea’s site was in trouble when Lee Doh-sik, the top North Korean geologist, visited Zhao’s institute about two weeks after the test and met privately with senior Chinese government geologists.

Although the purpose of Lee’s visit was not disclosed, two days later Pyongyang announced it would no longer conduct land-based nuclear tests.

Hu Xingdou, a Beijing-based scholar who follows North Korea’s nuclear programme, said it was highly likely that Pyongyang had received a stark warning from Beijing.

“The test was not only destabilising the site but increasing the risk of eruption of the Changbai Mountain,” a large, active volcano at China-Korean border, said Hu, who asked that his university affiliation not be disclosed for this article because of the topic’s sensitivity.

Yes, I could see China sending a message to North Korea telling them to STOP NOW, given possible radioactive fallout and potential volcanic eruption. And if China did say it, Kim Jong-un listened. We know he can’t afford to alienate China. So, with nuclear testing stopped at this one site (there are other sites, though) under likely Chinese pressure, one can speculate that Kim decided now was a good time to make nice with South Korea.

Any additional nuclear testing is going to be easy enough to verify (if it does start again), but what about the trust part? South Korea very much wants this to be real.

South Korea says it will remove propaganda-broadcasting loudspeakers from the border with North Korea. https://t.co/19uFNpfaen

— The Associated Press (@AP) April 30, 2018

Let’s just say that despite President Trump’s cheerleading talk, everyone else knows that they can’t count their chickens before they hatch when Kim Jong-un is involved.

Sec. of State Pompeo says Kim Jong Un is “going to have to make a big decision” on giving up nuclear weapons. “Does he want Pres. Trump to continue to place him in the location that he finds himself today? Or is he looking for something… different?” https://t.co/D8LGKBDPJo pic.twitter.com/UMnSsu3Aqd

— ABC News (@ABC) April 29, 2018

Rep. Schiff says Pres. Trump's "unpredictability" and "bellicosity" had something to do with North Korea's decision to negotiate. https://t.co/gYLfofd1e1 pic.twitter.com/Z8JuRTfUZA

— ABC News (@ABC) April 30, 2018

We have a very long way to go, but if China is indeed prodding North Korea from the back, then we’re already miles ahead of where we were just a few short months ago.