April 2016 – NORTH KOREA – An enigmatic and dangerous giant sleeps on the border between China and North Korea. It’s quiet now, but a millennium ago, the volcano called Mount Paektu exploded with a fury rivaling the largest eruptions in recorded human history, hurling crackling rocks and ash as far away as Japan. Despite that violent outburst, Mount Paektu—or Changbai, as it’s called in Chinese—remains fundamentally mysterious. Few outside the region are even aware it exists. And no one knows if, or when, the 9,000-foot-tall (2,740-meter-tall) peak might erupt again. Now, armed with an array of seismometers and almost unprecedented access to North Korea, an international team of scientists is working to peer beneath Mount Paektu. Inscribed in those shifting layers of Earth are crucial clues about the possibility of future eruptions.
“Is there magma down there? Is there melt that could potentially lead to an eruption? All the stuff that’s driving volcanic eruptions lives in the subsurface,” says Kayla Iacovino of the U.S. Geological Survey, coauthor of a study appearing today in Science Advances that describes Mount Paektu’s subsurface anatomy. Unlike most volcanoes on Earth, Mount Paektu isn’t located where tectonic plates collide. It’s parked in the middle of a plate, at least 620 miles (1,000 kilometers) away from the massive subduction zone that created the Japanese islands. Simply put, Mount Paektu shouldn’t really be there.
“That’s one of the big mysteries,” Iacovino says. For North Koreans, Mount Paektu is sacred. It’s their national emblem, and it is believed to be the birthplace of the founder of the first Korean kingdom. Small villages are sprinkled on its flanks, and in the summer, the surrounding area is covered in blueberries. Higher up, hot springs and gassy vents hint at the mountain’s still beating volcanic heart, and a pool called Heaven Lake sits in the crater at its summit. On the Chinese side of the mountain, there’s a national park that is a popular destination for tourists and hikers. “It’s a gorgeous place,” says Iacovino, who worked on the mountain in August 2013.
In many ways, Mount Paektu is pretty idyllic. But between 2002 and 2005, that tranquility came to a rumbling halt as a swarm of earthquakes shook the mountain’s slopes. Like a restless giant, though, whatever rumbled beneath the volcano rolled over and went back to sleep. Although it’s been slumbering since then, that seismic swarm was enough to alarm the normally reclusive North Korean government, which started speaking with neighboring countries and reaching out to the West. It was also enough to pique the interest of seismologist James Hammond, who was invited to study the slumbering beast. “It is a volcano with a dramatic past, showed some recent activity, and we do not know much about it,” says Hammond, of the University of London.
What Lies Beneath
After years of negotiations and bureaucratic wrangling, Hammond and a team of scientists finally had permission to enter North Korea and image the volcano’s subsurface, working alongside local colleagues. They arrived on the mountain in 2013 and deployed six solar-powered seismometers in a line stretching some 37 miles (60 kilometers) from end to end. For two years, those seismometers recorded the jiggles and shakes of earthquakes around the world, which sent seismic waves bouncing around Earth’s interior and making the planet ring like a bell. As such waves travel through the Earth, their speed varies depending on the type of rock they’re moving through.
When scientists collect data from a seismic array, they can use those slight variations in speed to figure out if the waves have been moving through solid rock or something more melted and gooey. Then they use all those data to piece together a picture of the layers beneath their feet. “We’re looking at where the melt—the stuff that could erupt from the surface—we’re imaging where that’s stored beneath the volcano,” Hammond says.
The data Hammond and his team have collected are solid, says seismologist George Zandt of the University of Arizona. And the results, though not particularly surprising, are nonetheless informative: Beneath Mount Paektu is a layer of partially melted rock—a mushy mixture of liquid, gas, crystals, and rock. “That sort of confirms the idea that the volcano is quite active,” Iacovino says. “But how much of it is ‘eruptable?’ That’s a big question.” Exactly how much magma there is and the size of the partially melted reservoir are still unknowns, and Hammond says he’d like to go back and do some deeper imaging.
It’s way too soon to say whether future eruptions are possible, but the partially melted magma suggests that whatever is fueling Mount Paektu’s outbursts isn’t quite yet done. And scientists say an explosion on the scale of the volcano’s A.D. 946 outburst could be catastrophic. “It could certainly influence things like international trade routes and commercial airline traffic, at least,” Iacovino says.
Understanding the potential for future eruptions means keeping a close eye on the volcano and continuing to peer at the layers beneath it. “I think the risk of a destructive eruption here is very real,” says seismologist Stephen Grand of the University of Texas at Austin. “The subsurface structure can help with predicting the future, although not with any definitiveness. One would need to follow how the current situation changes with time going forward.” –National Geographic