The volcano on the border of China and Korea erupted violently in the tenth century, and fell in 926. The pairing is tempting, and for years a link between them was proposed. Then the eruption was dated precisely. What came out?
A twenty-year gap, in the wrong direction. A tree trunk buried by the eruption carried from the year 775, and counting forward from it reached the year the tree died. Together with a marker in the ash and in Greenland ice, that puts the eruption in late 946, two decades after the kingdom fell.
The Millennium Eruption of Changbaishan was large, and for years its date drifted across different parts of the tenth century, which left room for every story anyone wanted to tell about it.
A tree buried at the time of the eruption supplied a clock. The anomalous carbon signal of the year 775 appeared in its rings, so the rings could be counted forward toward its death.
A chemical marker in a Greenland ice core supported a date in late 946. That is too late relative to the fall of the kingdom of Bohai in 926.
This is a case of why rough closeness in time is not enough to establish a cause. It does not say an eruption that large left other people in the region untouched, only that it cannot have ended a kingdom that was already gone.
wat. Twenty years lie between the collapse in 926 and the ash that fell in late 946, which is enough to end the story.
wat wat
A precise date can dismantle a historical story that sounds plausible only because two events happened in the same century.
How do we know?
The work combined tree rings, an anomalous carbon signal from the year 775 and chemical markers in Greenland ice layers.
What is still unknown
The dating rules out this particular cause for the fall of Bohai; it does not settle every regional consequence of the eruption.
Learn something?
Where to next
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