An international team of researchers has reconstructed an ancient super eruption in southern Italy that 39,000 years ago spewed a volume of ash and debris equivalent to eight Mt Everest’s into the air near Naples.

Over 1.1 million square miles, from the eastern Mediterranean Sea to what is now Siberia, were blanketed.

Blowing up from the Campi Flegrei, or Phlegrean Fields, on the Bay of Naples, the eruption created a four-mile-wide caldera and produced the cliffs on which the Camaldoli monastery now stands.

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The long-term global impacts were so intense that they slowed the westward migration of modern hominid groups in Europe.

“It was the largest volcanic eruption of the past 200,00 years in Europe,” Antonio Costa, a researcher of geophysics at the National Institute of Geophysics and Volcanology (INGV) said.

Costa and colleagues detailed their findings in the journal Scientific Reports. They analyzed more than 100 geological deposits from the dispersal area up to Russia, and found the samples featured two different grain size, one coarser and the other finer.

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“Such bimodal grain size distributions indicate two distinct phases of the eruption,” Costa told Discovery News.

He noted that previous computational studies wrongly characterized the eruption as a single-phase event.

Computer models created in collaboration with Barcelona Supercomputing Center (BSC) reconstructed the terrifying scenario in detail.

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Just like the eruption of nearby Mount Vesuvius that in 79 A.D. obliterated the city of Pompeii, the eruption of the “hidden” and still active supervolcano of the Phlegrean Fields began with a Plinian explosive phase.

In this phase, a mushroom cloud of fragmented rocks and gas raised up to 27 miles into the sky, injecting volcanic gas and ash into the stratosphere, which is the layer of the atmosphere above the one we live.

The fallout consisted of nearly 13 cubic miles of fallen deposits across over 500 thousand square miles, with lapilli and coarse ash covering what is now southern Italy.

Right after, a column made of fine ash particles separated from the devastating pyroclastic flows (fast-moving currents of hot gas and rock) raced up 23 miles high.

Rivers of superheated rock fragments, ash and gas spread up to 43 miles from the eruption site. About 37 cubic miles of finer particles were dispersed in this second phase.

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Overall, the super‐eruption covered an area of over 1.1 million square miles. The largest and thickest build‐ups of ash were in modern Macedonia, Bulgaria and Romania; in areas of the eastern Mediterranean layers up to 4 inches accumulated.

The huge eruption also injected large quantities of aerosols into the stratosphere, inducing a “volcanic winter” — with a cooling effect of up to 16.2 degrees Fahrenheit (9 degrees Celsius) in Eastern Europe and northern Asia.

Temperatures fell by about 7.2 degrees Fahrenheit (4 degrees Celsius) in Western Europe, and 1.8- 3.6 degrees Fahrenheit (1–2 degrees Celsius) globally.

“The effects were even more intense as the volcanic winter occurred during a glacial period, the Heinrich Event 4, which was already characterized by extreme condition and climate,” Costa said.

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The catastrophic event, however, was not responsible for the Neanderthals’ demise.

“The volcanic winter would not have been sufficient to trigger dramatic changes in Upper Palaeolithic European populations on a larger scale,” the researchers wrote.

However, ash and lapilli from the eruption reduced the area available for human settlement in Europe by up to 30 percent. The researchers calculated that about 10 years were necessary for an ecosystem recovery in most areas away from the source.

“It is possible that modern humans would have gravitated towards repopulating these recovered areas rather than resuming their westward dispersal, permitting prolonged Neanderthal survival in south-western Europe,” they wrote.

Neanderthal populations persisted in southern Europe well after the devastating eruption of the Phlegraean Fields.