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Ancient Roman, Chinese and Korean historical records are being used by Jet Propulsion Laboratory scientists along with ice core data to better understand the climatic impacts of very large volcanic eruptions during the Roman period and before.
Drs. Kevin D. Pang and David Pieri of JPL and Prof. Hung-hsiang Chou of the Department of East Asian Languages and Cultures at University of California, Los Angeles, presented their findings at the American Geophysical Union fall meeting in San Francisco, Tuesday, Dec. 9.
Previous reports have established good correlation between the historical dates of very large volcanic eruptions and the dates of their fallouts, as recorded in Greenland ice cores going back to the second millennium B.C., said Pang. "The climatic impacts of the 44- 42 B.C. eruptions of Etna are recorded not only in two deep Greenland ice cores, but also in tree rings, as well as Roman and Chinese chronicles. The data can serve as benchmark for understanding ancient eruptions."
The volcanic cloud from the 44 B.C. eruption of Etna began to form sometime after the death of Julius Caesar on March 15.
The Roman historian Plutarch wrote in about 100 A.D.: "Among events of divine ordering there was ... after Caesar's murder ... the obscuration of the sun's rays. For during all that year its orb rose pale and without radiance ... and the fruits, imperfect and half ripe, withered away and shriveled up on account of the coldness of the atmosphere."
A Roman history written in the Third Century A.D. and earlier Chinese and Korean records noted not only that daylight comet appeared near sunset during May and June following Caesar's death, but that its red color indicated there was already significant amount of volcanic dust in the atmosphere at the time.
The comet, called the "Julian Comet" was apparently bright enough to be seen at or before dusk, perhaps brighter than Venus. Its orbit has never been established.
From the Chinese chronicles of the Han dynasty, April, 43 B.C: "It snowed. Frosts killed mulberries." And from the same records month later: "The sun was bluish white and cast no shadows."
Pang, an astronomer, said the Chinese records, though less scrutinized, are far more voluminous than the European records.
In the search of historical literature, Pang said, scientists look not only for direct observations of volcanic eruptions but also for passages such as the excerpts from Plutarch and other Roman records and the Han dynasty chronicles.
Pang described the climatic impacts from large eruptions as very severe: "Cold summers, snowfalls and frosts in late spring and early autumn. Failed harvests and widespread famines were recorded as late as fall, 42 B.C. The approximate geographical distribution of the climatic impacts have been mapped using Han dynasty economic data."
The timeline reconstructed from the historical data dovetails with the acidity peaks and valleys of fallouts, recorded in the ice core, he said. Both the historical and ice core data suggest that the Etna volcanic cloud was sustained by multiple eruptions.
Pieri, volcanologist who makes annual trips to Italy to study Etna and other volcanoes, said that the field data are consistent with this interpretation.