Mount Paektu is a volcano on the border between North Korea and China, where the mountain is known as Changbaishan. A large depression at the summit holds a lake called Lake Chon in UNESCO’s North Korean geopark profile. English-language sources also call it Heaven Lake.
One of the volcano’s largest known explosions was the Millennium Eruption. Researchers narrowed its date to late 946 CE by combining evidence from a tree killed in the eruption with ice records and other clues. The mountain therefore offers two things to study together. One is the shape left by a major eruption. The other is how scientists work out when it happened.
- A caldera is a large volcanic depression, often formed when the ground collapses after magma leaves its reservoir.
- Ash carried by wind can leave a recognisable layer far from a volcano.
- UNESCO designated Mt Paektu Global Geopark in the DPRK in 2025. The volcanic system spans the international boundary.
UNESCO — Mt Paektu Global Geopark
Choose a reading route
Why the summit has a lake · Worked example: explain a date in three sentences · Frequently asked questions
Chapters 1–4 · Understand the subject
Chapters 5–7 · Work with the evidence
Chapter 1 of 7
Why the summit has a lake
Picture a mountain from the side, then picture it from above. From the side you see slopes rising to a high point. From above you may see a rim around a depression. At Paektu, the lake occupies that large summit depression. Once a volcanic depression exists, water can collect there. The age of the visible water and the history of the rocky basin are different questions.
A large eruption can remove enough magma for overlying rock to lose support and collapse. The result can be much wider than the opening through which material first escaped. On a diagram, draw a chamber below the summit, show material leaving and then draw the overlying ground dropping. This represents a general process. A field study is needed to establish the order and scale of collapses at a specific volcano.
UNESCO’s geopark description also draws attention to glacial landforms on the mountain. This matters when reading a photograph. A volcanic deposit and a hollow eroded by ice may both appear on one slope. One landscape can keep traces of several processes that took place at different times.
UNESCO — Mt Paektu Global Geopark
Chapter 2 of 7
Follow the ash away from the mountain
Volcanic ash is made of small fragments of rock, minerals and glass. During an explosive eruption, a rising plume can carry those fragments high above the source. Winds then transport some particles. Researchers have traced material from the Millennium Eruption across parts of East Asia, including deposits in Japan.
A thin ash layer can become a time marker. If the same eruption left material in two different places, matching the layers can tie the local records to the same event. A researcher can study the sediments beneath and above the layer at each site and compare what was happening before and after it arrived.
The match needs evidence. A light band in a soil core might resemble another band because both contain fine material. Researchers can compare the chemistry of the volcanic glass and the sequence of neighbouring layers. When they can identify the same eruption at multiple sites, geography gives them a second line of evidence about how the ash travelled.
Smithsonian Global Volcanism Program — Changbaishan
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Chapter 3 of 7
How a tree helped date the eruption
A tree grows outward in layers. In places with distinct growing seasons, successive rings can preserve a yearly sequence. The dating study identified a recognisable increase in radiocarbon associated with 775 CE within a larch killed and buried during the eruption. That event supplied a known year inside the wood.
The team could then count towards the outside of the trunk. Think of opening a set of loose annual journals and finding one dated entry in the middle. If the years have stayed in order, counting the entries takes you towards the end. For the tree, the condition of the outer rings and the circumstances in which it was killed are essential parts of the reasoning.
The study combined the tree evidence with other records, including ice. The different records have different strengths. Tree rings provide a sequence of years. Ice can preserve traces of volcanic emissions. Documents may record what people saw or heard at a given place, though matching a written observation to a particular volcano needs care. Late 946 CE is the result of bringing those lines of evidence together.
Oppenheimer and colleagues — dating the eruption
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Chapter 4 of 7
One volcano and several map boundaries
Search using both Paektu and Changbaishan. The first appears in North Korean and Korean contexts, while the second is common in Chinese and scientific sources. Papers may use both so readers can connect the names. If you are making a map, label the mountain and the two countries, then identify the summit lake separately.
The UNESCO Global Geopark in the DPRK has an administrative boundary. UNESCO also lists a Mount Paektu Biosphere Reserve through its Man and the Biosphere Programme. Each record has its own scope. A map of where the 946 ash fell answers a geological question and can extend far beyond any protected area. Comparing the maps starts with reading each legend.
UNESCO — Mount Paektu Biosphere Reserve
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Chapter 5 of 7
Worked example: explain a date in three sentences
Begin with the observation that a buried tree preserved annual rings. Explain that a radiocarbon marker supplied a year inside the sequence. Finish by saying the researchers checked the resulting date against other evidence and placed the eruption in late 946 CE.
Next to the explanation, put a diagram with two views. Use a cross-section to show why a caldera holds water. Use a simple regional map to show the difference between a volcano’s location and the area reached by its ash. Give each diagram a source and mark any sketch as schematic. Readers will be able to see how the same event can leave evidence at two very different scales.
Oppenheimer and colleagues — dating the eruption
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Chapter 6 of 7
Two phases and the layers they leave
Field studies distinguish two main explosive phases of the Millennium Eruption. That distinction matters when a textbook picture shows a single plume. A picture can represent one phase or simplify a whole event. The deposits allow researchers to ask whether early and later material differed and whether both phases sent ash high into the atmosphere. The paper linked below studies both phases as parts of the same eruption.
To follow that reasoning, sketch a vertical stack with the lowest layer at the bottom and the highest at the top. In a place where the layers have stayed in order, a lower layer usually arrived first. An ash layer’s position gives you relative order. Its composition can help identify it. Neither observation alone supplies a calendar date. For that, the tree-ring evidence helps connect the geological sequence to a particular year.
Research on the two eruption phases
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Chapter 7 of 7
From eruption history to monitoring
The historical record shows what the volcano has done over long periods. The Smithsonian’s Global Volcanism Program separates entries by event and source so readers can follow the evidence for different eruptions. When you consult its record, read the notes that accompany a date. The level of certainty can differ according to whether the event was observed directly, inferred from deposits or described in historical material.
Monitoring asks a present-tense question. Scientists can use observations such as earthquakes and changes in ground movement to study what is happening below the surface. A monitoring signal needs a timeline and context before it can be interpreted. The scale of the 946 event explains why Paektu is worth studying. Any assessment of current activity depends on current observations.
Make two cards for a class discussion. Put the eruption date and its main evidence on one card. Put a description of one monitoring method on the other. Comparing the cards shows why the date of a past eruption and a measurement made this year are useful for different reasons. Neither answer can be substituted for the other.
Smithsonian Global Volcanism Program — Changbaishan
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Frequently asked questions
Are Paektu and Changbaishan the same volcano?
In this guide the names identify the volcano that spans the North Korea–China border. Research articles often include both names.
Why is it called the Millennium Eruption?
The name reflects the eruption’s approximate placement around the turn of the millennium. Later research narrowed the date to late 946 CE.
Is the geopark a World Heritage inscription?
It is a UNESCO Global Geopark designation. UNESCO runs a separate World Heritage programme.
Sources and next reading
Primary sources
- UNESCO — Mt Paektu Global Geopark
- Oppenheimer and colleagues — dating the eruption
- Smithsonian Global Volcanism Program — Changbaishan
- UNESCO — Mount Paektu Biosphere Reserve
- Research on the two eruption phases