El Chichon eruption implicated in Mayan upheaval

http://www.bbc.com/news/science-environment-36086096

El Chichon eruption implicated in Mayan upheaval

By Jonathan Amos
BBC Science Correspondent, Vienna
2 hours ago

Scientists think they can now tie the disruption that hit Mayan civilisation in the 6th Century to an eruption of the El Chichon volcano. A Dutch team has investigated ash fall deposits, finding the age of the materials to be a good match for the so-called Mayan "hiatus". This was a time when the sophisticated central Americans experienced cultural upheaval and political instability. They also abandoned many of their favoured lowland sites.

A sulphur spike in ice core records from the poles indicates there was a big eruption somewhere on Earth in AD 540 - right at the start of the multi-decade hiatus. It must have been a major event to have left such a distinctive signature in the frozen layers, and very likely led to global climate impacts and severe environmental degradation in the region of the blast.

Previous research has offered up Ilopango in El Salvador as the culprit. Radiocarbon dating of tree remains puts this volcano in the vicinity timewise - but not convincingly so, argues Kees Nooren from Utrecht University. Instead, he is pointing the finger at El Chichon in southern Mexico, a case he has outlined here at the European Geosciences Union General Assembly. His research centres on ash fall dispersed across what were the Mayan lowlands. This tephra can be connected chemically to the 1,200m-high volcano. Samples have been collected from Lake Tuspan and the Usumacinta-Grijavala delta on the Mexican coast.

Using multiple techniques, not just radiocarbon, Mr Nooren tightly packs the ages of the ash fall around AD 540. "We already had dates from proximal deposits near the volcano and now we have dates for distal deposits, and when you combine them you get a date of AD 546, plus or minus 16," he explained. "So, we have a very narrow window, which means it is very likely there was a large eruption in 540."
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Dr Toohey says there are actually two closely spaced signatures in the ice record, with the second occurring in AD 536. This event could be an eruption somewhere in North America, perhaps Alaska.
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"We estimate that if you take these two eruptions together and look at their impact over a 10-year period, focusing on the Northern Hemisphere - then this double event would have been clearly the strongest volcanic forcer of climate of at least the last 1,200 years, probably more like 2,000 years."