The study led by Professor Martin Williams of the University of Adelaide shows the eruption of the volcano Toba, located on the island of Sumatra, ejected about 192 cubic miles of ash into the atmosphere, leaving a crater -- now the world's largest volcanic lake -- that's 62 miles long and 21 miles wide. Ash from the event has been found in India, the Indian Ocean, the Bay of Bengal and the South China Sea.
The researchers said the bright ash ejected from Toba reflected sunlight off the landscape and volcanic sulfur aerosols impeded solar radiation, initiating an "instant ice age" that lasted about 1,800 years.
University of Illinois anthropology Professor Stanley Ambrose, a principal investigator of the study, said a carbon isotope analysis showed forests that covered central India when the eruption occurred disappeared for at least 1,000 years afterward.
"This is unambiguous evidence that Toba caused deforestation in the tropics for a long time," Ambrose said, noting humans were close to extinction following the disaster, which might have forced the ancestors of modern humans to adopt new cooperative strategies for survival that eventually permitted them to replace Neanderthals and other archaic human species.
The research is reported in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.