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Volcano implicated in Maya upheaval

BBC News BBC News 21/04/2016 By Jonathan Amos
Volcanic eruption © Getty Images Volcanic eruption

Scientists think they can now tie the disruption that hit Maya 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 Maya "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 Maya 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."

El Chichon last let go in spectacular style in 1982, destroying local communities and killing 2,000 people.

It spewed vast quantities of sulphur dioxide and other particulates into the atmosphere.

The AD 540 eruption would have been much bigger, the Utrecht researcher said.

Whether El Chichon really is the source of the sulphur seen in the ice cores would require a chemical analysis that has yet to be done, commented Matthew Toohey from the GEOMAR Helmholtz Centre for Ocean Research in Kiel, Germany.

The best one can say at the moment is that the event was probably located in the tropics, he told BBC News.

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.

Killer peaks

Over the last four decades, 900 people a year have been killed by volcanic eruptions.

In addition to lava flows - mudslides, ash clouds and pyroclastic currents can be deadly.

BBC iWonder: What are the four ways a volcano can kill?

His interest is trying to model the climate disruption that stems from volcano blasts.

When he does this for the "double event" of AD 536 and 540, his simulations come out in good agreement with historical archives.

Tree ring data in northern Europe from this time indicates there was very strong cooling - something you might expect if large volumes of sulphate aerosols were dispersed across the globe.

Archaeological evidence and other information also speak to societal disruption, such as a run of poor harvests and outbreaks of plague.

Dr Toohey said his simulations suggested there was a reduction in average summer temperatures across Northern Europe of two degrees.

"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."

Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos

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