MOUNT PAEKTU, a dormant volcano which straddles today’s border between China and North Korea, has long been considered a holy place. The mountain, and the lake at its summit, are revered by North and South Koreans as the birthplace of Tangun, the mythical founder of Korea. It still features in the opening verse of South Korea’s national anthem. In North Korea it is taught that, in the 1930s, Kim Il Sung led an anti-Japanese guerrilla movement under the cover of Mount Paektu’s dense forests, and that his son, Kim Jong Il, was born in a hut on its flanks. The Chinese too, who call it Changbaishan, have long prized it. Hikers and pilgrims visit, though the border has not been without dispute. After the war that split Korea in two in the 1950s, the North agreed to a new border with China across the middle of the lake, a solution which still angers many Koreans.

As the nationalistic tussle rumbles on, Mount Paektu has begun to make noises of its own. A decade ago its flanks bulged as a series of tiny earthquakes raised the alarm. The North Korean authorities have become sufficiently worried to extend a rare invitation to a pair of British scientists, who visited North Korea’s volcano observatories in 2011. They returned in August this year to install six seismometers, which are to record tremors for a year. Waves from distant earthquakes will illuminate the structure of 100km (62 miles) of earth crust and mantle beneath the volcano. If tests show a shallow body of molten rock below, for instance, that could suggest Mount Paektu is gearing up for another explosion (its last, around 940AD, covered a swathe of North-East Asia in ash).

There are other puzzles for the vulcanologists to investigate. Mount Paektu is far from the edge of the Pacific plate, a lively tectonic boundary, which makes the power of its past eruptions a mystery. Clive Oppenheimer, one of the British scientists who made the trip, is analysing ash and pumice that he collected there.

Their trip faced some challenges. Bringing their gear into Pyongyang was tough, says Mr Oppenheimer. Laptops were scrutinised against the terms of international sanctions (a device that measures electromagnetic fields did not make it through). The North prohibits flash memory sticks. The British scientists could not e-mail colleagues in Pyongyang directly to plan fieldwork. And data is allowed to be sent to Britain only once every two months.

Across the border, China has been monitoring the mountain since 1999. It now has 11 seismometers stationed on its side. But Xu Jiandong, a vulcanologist at the China Earthquake Administration (CEA) in Beijing, says the North Korean portion of the volcano has been a “black spot”. The North’s chunk—about a third of the volcano—is usually barred to outside scientists. Data-sharing, says Mr Xu, has been non-existent. In 2011, after a tsunami struck Japan, there was talk of North and South Korea starting a collaborative monitoring programme, but that has since stalled. The North refused China’s offer of a seismometer six years ago. Mr Xu suspects that is because its nuclear test site is just 70km away. Though seismometers on the Chinese side could detect underground activity anyway, more stations would allow for finer readings of a nuclear test.

For all that, Mr Xu deems the British project a breakthrough. He calls it “our first indirect collaboration with the North”. The Chinese government has already rejected two official requests by the CEA for permits to work there (though North Korea granted Mr Xu a visa earlier this year). As well as delivering data about the volcano, Mr Oppenheimer hopes his project will ease exchanges between his scientific collaborators in Pyongyang and their counterparts in China, who are due to visit Britain later this year. A geothermal sort of geopolitics, then, to help thaw relations.