A North Korean national television crew records from Mount Paektu, the site of one of the biggest eruptions in human history. Two British scientists recently completed a rare effort to study the volcano. (David Guttenfelder/AP)

— More than a thousand years ago, a volcano on the border between North Korea and China was the site of one of the biggest eruptions in human history, blanketing eastern Asia in its ash. But the remote and politically sensitive Mount Paektu remains almost a complete mystery to foreign scientists who have — until recently — been unable to conduct on-site studies.

Fresh off their third visit to the mountain, two British scientists say they may soon be able to reveal some secrets of the volcano, including its likelihood of erupting again. In an unprecedented joint project with North Korea, they’re collecting seismic data and studying rocks ejected in Paektu’s “millennium eruption” sometime in the 10th century.

“It’s one of the biggest eruptions in the last few thousands of years and we don’t have yet a historical date for it,” Clive Oppenheimer, a professor of volcanology at Cambridge University, said after returning to Pyongyang from an eight-day trip to the volcano.

“The rocks are a bit like the black box of a flight recording,” he said. “There’s so much that we can read from the field site itself.”

For volcano researchers, studying Paektu is a golden opportunity because so much about it remains a puzzle.

More than a thousand years ago, a huge volcano straddling the border between North Korea and China was the site of one of the biggest eruptions in human history, blanketing eastern Asia in its ash. (David Guttenfelder/AP)

Oppenheimer said Paektu is not located along any of the tectonic features that often explain volcanic activity, so just figuring out why it exists at all is one question that needs to be answered. There is little or no historical information about the millennium eruption, so scientists are also interested in learning exactly what happened, what the volcano and the ecosystem around it were like before the eruption and how life returned afterward.

Paektu is considered sacred ground in both China and North Korea. North Koreans also see it as a symbol of the ruling Kim family and of the founding of the country. On the North Korean side, the area around the mountain is dotted with “revolutionary historical sites” and secret camps from which Kim Il Sung, North Korea’s first leader, is said to have led guerrilla attacks against the Japanese, who held the Korean Peninsula as a colony until the end of World War II.

Tens of thousands of North Koreans visit the mountain for political indoctrination tours every summer. North Korea is also hoping to develop the volcano, which has a crystal blue crater lake, for foreign tourism.

Fears that the 9,200-foot mountain might be unstable began to grow in 2002, when increased seismic activity and ground swelling suggested that the magma below the volcano was shifting. That activity subsided in 2006. Concerns were raised in South Korea and Japan that nuclear tests in the North — conducted at a site about 60 miles away — might trigger an eruption.

“That activity sparked a lot of interest both in China and [North Korea] but also in Japan and South Korea and internationally,” said Oppenheimer’s colleague James Hammond, a seismologist at Imperial College London. He added that fears of a major eruption soon are probably unfounded. “It’s certainly very tranquil at the moment.”

Even so, Hammond said the activity prompted the North Korean government to reach out to the international scientific community for help in understanding Paektu’s inner workings. Until the 2002 activity, little scientific research on the volcano had been conducted by China or North Korea.

The project got underway in 2011 at the request of a North Korean government agency, the Pyongyang International Information Center on New Technology and Economy. With funding from the Richard Lounsbery Foundation, a Washington-based philanthropic organization that supports the sciences, Oppenheimer and Hammond became the first Westerners to visit the North’s six field stations on the volcano.

Hammond said that although he was intrigued by the opportunity, the project was a logistical challenge, and not only because of language differences and North Korea’s unfamiliarity in dealing with foreign researchers. International sanctions on the North over its nuclear weapons program also made it difficult for the scientists to bring in some of the equipment they wanted because of concerns they could have dual-use applications that might benefit the North’s military.

“If we want to understand what the volcano is like today, we need to park instruments on the ground,” Hammond said. “Building the models of what happened previously allows us to address what might happen in the future.”

Last September, Hammond installed six broadband seismometers to record activity on the volcano, while North Korea’s Korean Earthquake Bureau built protective huts for the equipment. He also collected samples of pumice that might provide insight into the scale of the millennium eruption, which is believed to have occurred between the years 930 and 940.