The Toba supervolcanic eruption about 74,000 years ago was one of the most colossal eruptions in the past 2 million years.
The massive eruption at the site of present-day Lake Toba in Sumatra, Indonesia spewed an estimated 1,000 times as much rock as the 1980 eruption of Mt St Helens and, many believe, triggered a decade-long “volcanic winter” and a millenia-long glacial period.
This so-called Toba catastrophe theory left the global human population with just a few thousand survivors.
However, an ancient stone tool industry uncovered at Dhaba in northern India suggests that humans have continuously occupied the Middle Son Valley for roughly 80,000 years, both before and after the Toba eruption.
“Populations at Dhaba were using stone tools that were similar to the toolkits being used by Homo sapiens in Africa at the same time,” explains archaeologist Chris Clarkson from the University of Queensland.
“The fact that these toolkits did not disappear at the time of the Toba super-eruption or change dramatically soon after indicates that human populations survived the so-called catastrophe.”
At about the same time as the Toba eruption, our species was also going through a genetic bottleneck, an unmistakable drop in human genetic diversity, and the eruption seemed like a plausible cause for this drop in diversity.
But the authors say the thousands of stone tools found in Dhaba suggest that humans migrated out of Africa and expanded across Eurasia much earlier than expected, and that the Toba eruption did not, I repeat, did not, lead to extreme cooling, nor trigger a glacial period.
The study by Clarkson et al. was published in 2019 in Nature Communications. ( https://www.nature.com/articles/s41467-020-14668-4 )
For the time being, I think I’ll stick with the millenia-long glacial idea. According to Wikipedia, geologist Michael R. Rampino and volcanologist Stephen Self think the eruption caused a “brief, dramatic cooling or ‘volcanic winter'”, which resulted in a drop of the global mean surface temperature by 3–5 °C. Evidence from Greenland ice cores indicates a 1,000-year period of low δ18O and increased dust deposition immediately following the eruption. The eruption may have caused this 1,000-year period of cooler temperatures (stadial), two centuries of which could be accounted for by the persistence of the Toba stratospheric loading.