The puzzle around the date of a huge volcanic eruption in East Asia has been solved by a team of international researchers who traced its date to within three months.
The Changbaishan volcanic eruption was the most violent burst in the last two thousand years. But when exactly the volcano erupted had remained an enigma for historians.
The belief was that the eruption, also called the "Millennium Eruption" because it was thought to have occurred in approximately 1000 CE, brought down an important 10th-century kingdom.
However, the new date determined by the researchers showed that the theory had no basis as the volcano erupted much later after the fall of the Bohai kingdom, which ruled from 698-925 AD over many parts of eastern Manchuria and northern Korea.
The volcano sits on the border between China and North Korea and is also known as Mount Paektu.
Clive Oppenheimer from the University of Cambridge's Department of Geography led the researchers who were out to determine the accurate date of the volcano's eruption.
The team proved the date of volcano's eruption using radiocarbon measurements. The findings were published in the journal Quaternary Science Reviews.
Unlike earlier studies that sought to analyze the eruption, the new study was helped along by the cosmic radiation that showered the Earth in 775 AD. So far the historians have been scratching medieval texts to ferret out clues on the volcanic eruption.
The team analyzed semi-fossilized vestiges of a tree that died in the eruption and also used ice cores excavated from Greenland to advance their investigation. Through the radiocarbon measurements on the fossilized trunk of a larch tree found at the site, the researchers concluded that the tree was 264 years old when it was run over by lava, the hot and flowing material from a volcano.
Cosmic Effect On Tree
The team inferred that the tree might have been in existence since 775, the year when a burst of cosmic rays reached Earth. The marks of the natural event were obvious with the presence of radiocarbon in one of the tree's rings. From there, the researchers counted to the tree's outer ring to know the year in which the tree perished. They concluded that the tree's death was in the autumn or winter as the seasonal growth was found halted.
They also corroborated the data with ash deposits found in the ice cores in Greenland and zeroed in on the probable date of eruption to the last two or three months of 946 AD.
Because the findings debunks the theory that the eruption contributed to the fall of the Bohai kingdom in 925 AD, the team turned to a written account that could verify the eruption's date. On Nov. 3, 946 AD, a Japanese temple chronicle noted the presence of "white ash falling like snow."
Considering the temple was nowhere near any active volcanoes in Japan and is near places where ash from the eruption has been identified, the chronicle could provide the actual date of the Changbaishan volcanic eruption. The ash mentioned in the report could be from the eruption, as the ash clouds would have reached Japan in a day or so.
"Now we have a secure date for the eruption at last, we can be more confident in investigating the effects it has on the climate, environment and society," said Oppenheimer, the study's lead author.