Volcanic eruptions can be bad for more than the unlucky people living in their shadows—in 1816, ash from the eruption of Mount Tambora in Indonesia blotted out the sun and led to a "year without a summer" as far away as Vermont. The massive eruption of Krakatoa, also in Indonesia, in 1883 lowered summertime temperatures across the world and disrupted weather patterns for years. But those eruptions—and pretty much any others—pale in comparison to Toba, a volcano that erupted on Sumatra in Indonesia 74,000 years ago. It was believed the disruptions caused by the super-eruption likely pruned a few branches off the early human family tree. But new studies reveal that Toba's impact might have been exagerrated. In fact, reports George Dvorsky at Gizmodo, research shows early humans did quite well during the disruptions caused by the volcano.
Toba was no ordinary eruption. It spewed thousands of tons of ash into the atmosphere, enough to create a decade-long volcanic winter, leading to massive die-offs of vegetation and the end of some species. That was followed by up to one thousand years of cooler than normal temperatures. The event was so extreme that some researchers believe that it reduced the global human population to just a few thousand survivors, a hypothesis called the “Toba catastrophe theory."
But according to a study published in the Journal of Human Evolution, none of that may be true. Researchers re-examined sediment cores drilled from Lake Malawi in East Africa. Previous studies had identified crystals and glass from the Toba eruption in those cores. Looking at microscopic bits of plant matter preserved in the cores, the researchers were able to look at vegetation levels 100 years before and 200 years after the eruption. What they found is that there was no cooling or massive die off. It seems the massive explosion did not impact east Africa at all, except for alpine areas.
“This is the first research that provides direct evidence for the effects of the Toba eruption on vegetation just before and just after the eruption,” Chad L. Yost, a doctoral candidate at the University of Arizona and lead author of the study, says in the release. “The Toba eruption had no significant negative impact on vegetation growing in East Africa.”
In other words, the cores indicate the volcanic winter never took place, or was mild enough not to show up in the sediment record. Another recent article in Nature shows that during the post-Toba time period early humans were actually thriving, reports Gretchen Vogel at Science.
Archaeologists at two sites in South Africa—a series of coastal caves inhabited by early humans called Pinnacle Point and an open-air site called Vleesbaai—sampled the sediments until they found microscopic evidence of the Toba eruption. Using a relatively new technique called optically stimulated luminescence, which indicates the last time a grain of sand was exposed to sunlight, researchers were able to show that the two sites were occupied at the time of the eruption.
What researchers found is that Toba did not interrupt the human occupation at the sites, and in fact, during the immediate aftermath of the catastrophe, human occupation intensified. “This is the first time we can say: Here is what humans were doing before and after [the eruption],”co-author Christine Lane from the University of Cambridge tells Ed Yong at The Atlantic. “And I think we were doing really well.”
Not everyone interprets the data the same way. Vogel reports that Stanley Ambrose of the University of Illinois, one of the originators of the Toba catastrophe theory, argues that layers of sand above the ash indicates climate change at the Pinnacles site and a decrease in population.
But Yost, author of the core sample study, says his work and the archaeology sites are painting a new picture of the Toba eruption. “The datasets from our research and the Nature paper complement one another and together indicate that the Toba supereruption had little effect on the climate of Africa and the humans who were living there,” he tells Dvorsky. “Where the two studies diverge has to do with interpreting the magnitude of climate change from the Toba eruption.”
While Yost and his team argues that there was no significant volcanic winter effect, according to a press release, the Nature authors argue that the eruption did lead to significant climate shifts and the sites in South Africa served as refugia for human populations, who were able to survive by exploiting the food-rich coastline. If that’s the case, the researchers hope to find other sites along the coast where the rag-tag remnants of the human race held on during the long, dark winter.
An earlier version of this article gave the wrong location for Mt. Tambora; it has since been corrected.