Humans Spared Worst of Volcanic Supereruption 74,000 Years Ago

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The largest volcanic eruption of the past 2 million years occurred roughly 74,000 years ago in what is now Indonesia. Called the Toba supereruption, its effects on the world -- and specifically, on human evolution -- have been hotly debated. Now scientists find that although the event likely caused severe global climate disruptions, humans were apparently sheltered from the worst effects.

The eruption of the Toba supervolcano on the island of Sumatra expelled roughly 5,300 cubic kilometers (1,300 cubic miles) of magma, a greater volume than Lake Michigan. Ash from the explosion reached an altitude of up to 40 kilometers (25 miles), where it could have blotted out the sun and drastically cooled the Earth for years -- a "volcanic winter."

The eruption took place at a critical point in history, when modern humans were poised to expand more broadly out of Africa. Some researchers have suggested the catastrophe might have influenced the course of human evolution, with people today evolving from the few thousand survivors of that disaster, while others have found no signs that it endangered our species.

In the new study, researchers developed 42 global climate model simulations of the supereruption's potential effects over the course of a decade. These included a variety of background climate conditions, levels of volcanic emission, and altitudes the discharge reached. They also considered different possible times of year for the eruption, to account for seasonal changes in atmospheric circulation.

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