Matthew Morris investigates the mystery magma behind Mount Paektu
Mount Paektu, also known as Mount Changbai, is a stratovolcano located directly on the border between China and North Korea. The volcano has immense cultural significance to the Korean people; it is mentioned in both the North and South Korean national anthems. However, its geological setting has been a mystery to scientists for decades.
Many of the world’s most dangerous volcanoes are concentrated along the infamous ‘ring of fire’– a chain of volcanoes located above subduction zones, where oceanic tectonic plates are descending down, or subducting, beneath the less dense continental plates. Volcanism occurs at subduction zones due to water released from the subducting oceanic plate melting the overlying mantle. This forms magma which can rise through the crust, causing devastating eruptions. Other volcanoes, such as Kīlauea in Hawaii, are found away from subduction zones and are the results of mantle ‘hotspots’. Volcanoes are also found along divergent plate boundaries, such as the Mid-Atlantic Ridge or the East African Rift Valley, where the crust is very thin.
These three forms of volcanism should account for the location of every volcano on Earth. However, as is always the case with nature, there are outliers. Mount Paektu is over 500 km from the nearest subduction zone, with no observed crustal thinning, and no identified mantle plume. So, why is there volcanism?
Understanding this volcano is not just of scientific intrigue; Mount Paektu is still active and a large eruption could put many larger cities, including Seoul and Beijing, at significant risk. Its 946 A.D. eruption was one of the largest eruptions ever recorded as it produced enough tephra to blanket an area the size of New York City in almost 150 metres of ash. Unfortunately, the volcano has historically been off-limits to geologists wanting to study its inner workings. Both China and North Korea have traditionally been hostile to international research efforts. But following increased activity during the early 2000’s, the North Korean government took an unprecedented step to call on the wider science community for help in understanding the volcano and its potential risk. After years of visa issues and coordination, in 2011 two scientists from the UK, James Hammond and Clive Oppenheimer, joined North Korean scientists to uncover Mount Paektu’s hidden secrets.
Thanks to the international cooperation, our understanding of this volcano is much clearer. Using an analytical technique called seismic tomography, it is now thought that a portion of subducting oceanic plate has travelled much further laterally than expected, in an area known as the Mantle Transition Zone. However, there is still significant debate regarding this, as recent tomography shows a possible hole in the subducted plate, potentially generating magma through an entirely different process.
Although the geological findings are important, there are wider issues to address here, namely the importance of international co-operation for the advancement of science. This is a problem that takes many forms, including the issue of primarily western scientists not engaging with local researchers when studying in developing countries. For the good that comes out of scientific advancement, we must ensure everyone is involved and there are no barriers for global research.
From Issue 22: the Dark Side of Science