A team of Western scientists got a rare invitation to North Korea to study the massive volcano known as Mount Paektu. According to a report from the Washington Post, a recent study from a team of scientists from North Korea, China, the U.S., and England reveals what exactly is lurking below the surface of the mountain.

Researchers believe that the last time the volcano erupted was in roughly 946 A.D. It has towered on the border of North Korea and China in relative silence ever since, but rumblings in the early 2000s prompted concern from North Korean scientists.

After years of diplomatic efforts, the team of Western scientists was allowed access to Mount Paektu to survey the geologic makeup of the volcano. According to one of the study’s co-authors James Hammond from the University of London, “It was quite a special experience the first time. Very much a voyage into the unknown.”

The recent survey is the first of its kind, using modern techniques to map out the subsurface features of Mount Paektu. Researchers say that there were no pockets of liquid magma directly under the surface, which is a typical sign of an impending eruption. They were, however, unclear as to how the flows of magma were situated deep below the crust of the mountain.

“One of the challenges now is to go beyond simply saying there’s magma n the curst, discovering instead how it’s sitting, how much there is and what are the implications,” said Hammond. “It’s only when it gets to a certain amount and a certain overpressure that it will erupt.”

Mount Paektu isn’t like other volcanoes. The majority are situated on the fault lines between tectonic plates, where hot magma flows out toward the surface of the Earth. Researchers believe that Mount Paektu is situated on a hot spot in the Earth’s mantle.

While there is no immediate threat of Mount Paektu erupting in the immediate future, scientists remain wary of the possibility of unseen forces at work.

The study, published in the journal Science Advances, can be found here.