In 2011, when North Korean dictator Kim Jong Il died, the state news agency reported that Mount Paektu took on a supernatural glow, and that at its summit, Heaven Lake shook with cracking ice.

Those reports were pretty unscientific. But several years earlier, between 2002 and 2005, Mount Paektu had experienced a swarm of little earthquakes.

That wasn't a good sign, because the 9,000-foot mountain straddling the border with China is not merely the subject of paintings and patriotic songs — it's also a huge volcano. And little earthquakes can be a sign that, deep under the mountain, molten magma is starting to swirl.

"That can possibly lead to an eruption, so people in the region — including North Korea — started becoming a little bit wary of the activity of the volcano," says Kayla Iacovino, a volcanologist at Arizona State University.

The North Koreans became nervous enough to do something they never do — ask Western scientists for help finding out when and if the volcano might blow. In 2011, through both the Pyongyang International Information Center on New Technology, and Economy and the Environmental Education Media Project in Beijing, they invited a group of volcano scientists to visit.

But you can't just hop on a plane to North Korea, says Iacovino, who is American but at the time was doing doctoral research at the University of Cambridge in the United Kingdom.

She says it took about two years of back-and-forth with authorities on both sides before permission was granted. North Korea doesn't trust Western governments, and the British worried about unauthorized technology getting into North Korean hands.

There's a lot of fear and mistrust, says Iacovino, but it's not among the scientists.

"All of us were kinda like, 'We just wanna measure volcanoes,' " she says.

But countries including the United Kingdom and United States have rules against bringing technology into North Korea that could be used for military applications. So Iacovino and her colleagues had to ditch their beloved magnetotelluric sounder, a device that's useful for finding things you can't see, like pockets of underground magma — or submarines.

Eventually they worked it all out, and Iacovino and her colleagues packed up the rest of their top-notch equipment and went to Mount Paektu in 2013.

They hiked for about a week with North Korean geologists, chatting about rocks, enjoying the wild blueberries and setting up seismographs to map out the volcano's plumbing and gain insight into the possibility of imminent eruptions.

"It's really unprecedented what we were able to do in the country," Iacovino says.

North Korean government translators did accompany them everywhere, and they were limited to using restaurants and hotels built for foreigners. Communicating with their North Korean collaborators after the trip hasn't been easy. They can't just email or pick up the phone — all communication has to go through NGOs.

Still, this kind of collaboration is really important, says Stuart Thorson, a professor emeritus in political science at Syracuse University — not just for evaluating the potential threat of one volcano, but also because science can help build trust between countries.

"Even during the '50s and '60s, when there was all this tension, U.S. and Soviet scientists were moving back and forth between each others' laboratories," he says. "Ultimately that provided some of the trust and the basis for being able to enter into arms negotiation, arms limitation treaties."

Thorson himself has worked for years with scientists in North Korea and has traveled there 10 or 11 times, first to help Kim Chaek University of Science and Technology set up North Korea's first digitized library, and later to coach researchers in English and PowerPoint so that they could attend international science conferences.

Other American universities have collaborated with academics in the country — Stanford University helped build a laboratory to diagnose and track drug-resistant strains of tuberculosis, which is a problem there — but the Syracuse and Stanford collaborations have fallen to the wayside in recent years, partly owing to funding issues.

Thorson says the collaboration to study Mount Paektu is notable because bringing sophisticated scientific equipment into North Korea is no small accomplishment.

"They're exhibiting enough trust to allow instrumentation into their country, which is something they've been very resistant to," says Thorson.

The latest fruit of the volcano collaboration came out Wednesday in the journal Science Advances.

The gist of the paper, which is co-authored by scientists in the United States, United Kingdom, China and North Korea, is that about 1,000 years ago Mount Paektu exploded, big time.

"We can now say that the eruption of Paektu was probably one of the largest eruptions in the last couple thousand years — not only in terms of the ash and rock output, but also in terms of the gas output," says Iacovino.

There are no big eruptions in sight, she says, despite the series of small earthquakes that started more than a decade ago at the mountain, but there is a spacious, active magma chamber deep below the mountain. Iacovino hopes the international collaboration with North Korea will continue, because volcanoes don't care about borders.

Copyright 2021 NPR. To see more, visit https://www.npr.org.