Roughly 74,000 years ago, the Toba supervolcano erupted on the island of Sumatra in modern-day Indonesia, releasing an enormous amount of ash into the atmosphere. This ash settled in different parts of the world—including southern and eastern Africa, where communities of Homo sapiens lived. 

These humans were far enough away from the supervolcano to survive its destructive eruption, but not to escape its effects on global climate. The Toba supervolcano led to more arid weather and possibly cooler temperatures in parts of Africa. In the late 1990s, one scholar proposed that the supervolcano’s effects may have caused a “volcanic winter” that pushed humans to the brink of extinction.

More recent research suggests the climate changes caused by the supervolcano were much milder than a “volcanic winter,” and that humans adapted their behavior so successfully to these changes that they didn’t come close to extinction. They not only survived the supervolcano’s effects, but may have actually thrived during them.

A supervolcano is any volcano that has had a “supereruption” of more than 1,000 cubic kilometers of rock, ash and other debris, according to the U.S. Geological Survey. Sites of prehistoric supervolcano eruptions include Yellowstone in the United States, La Pacana in Chile and Taupō in New Zealand.

The Toba supereruption 74,000 years ago is known as the “Youngest Toba” because it is the most recent volcanic eruption at that location. Today, the site of the Youngest Toba is a body of water known as Lake Toba that formed in the volcano’s caldera.

There is currently no evidence that any humans or human ancestors had migrated as far as Sumatra in Indonesia when the Youngest Toba blew its top. (And if any had been near the eruption, they likely would’ve died.) Most of the research into how humans survived Toba has focused on Africa, where the supervolcano’s eruption caused some changes in climate.

A key discovery that has allowed archaeologists to study how humans survived the Toba supervolcano is cryptotephra—tiny pieces of glass from a volcanic eruption. The late geologist Gene Smith identified cryptotephra from Toba in sediment found at African archeological sites. These pieces are so small that you can’t see them with the naked eye.

“If you plucked a hair out of your head, that’s going to be about 100 microns in diameter or so,” says John W. Kappelman Jr., a professor of anthropology and geological sciences at the University of Texas at Austin who worked with Smith. (A micron, or micrometer, is equal to one-millionth of a meter.)

“The glass that Gene was able to recover…is on the order of 20 to 50 microns in size,” he says. “So imagine under a microscope, lining up five of these little crystal pieces of glass, and that would equal the diameter of a human hair.”

The discovery of cryptotephra at archaeological sites in southern and eastern Africa allowed researchers to date parts of those sites to before, during and after the Toba eruption. What they found was that humans in modern-day South Africa and Ethiopia successfully adapted to temporary changes caused by the Toba supervolcano.

In 2018, Smith and his colleagues published a paper in Nature arguing that humans in South Africa didn’t just survive the Toba eruption, but actually “thrived” in its aftermath. They argued that artifacts at two archaeological sites—Pinnacle Point and Vleesbaai—show humans developed technical innovations to their tools shortly after the Toba eruption. These innovations had a lasting impact, as humans at these sites continued to use them for thousands of years.

A 2024 paper in Nature by Kappelman, Smith and other researchers provided even more detail about how humans adapted to changes caused by Toba. Kappelman says the Toba eruption caused the climate to become more arid at a site in Ethiopia now known to archaeologists as Shinfa-Metema 1. This increased aridity caused rivers to dry up into smaller waterholes, trapping fish inside. Humans responded by changing their diet to mostly fish, since these temporarily became the easiest prey to hunt.

Before the Toba eruption, Kappelman says humans at the Ethiopian site ate mostly land animals like antelope, pigs and monkeys, with only a small portion of their diet coming from fish. But for a year or two after Toba, these humans switched to eating fish as a primary food source. When the climate shifted back to pre-Toba conditions, rivers returned to their normal patterns and humans went back to eating more land animals and fewer fish.

“Most hunter-gatherers are good economists,” Kappelman says of this switch to fish. Humans at Shinfa-Metema 1 probably ate whatever was easiest to catch, and during the extended dry season caused by Toba, the easiest catch became fish. “It’s literally like fish in a barrel,” he says of the region’s dry season waterholes. The fish “are stuck in the waterhole itself and the river’s not flowing.”

In 1998, anthropologist Stanley H. Ambrose published a paper in the Journal of Human Evolution arguing that Toba had caused a “volcanic winter” that could have brought humans close to extinction. Since then, more recent research has shown that, at least in Africa, Toba did not cause the kind of extreme climate changes Ambrose proposed.

Although Kappelman and his colleagues found that the climate at Shinfa-Metema 1 in Ethiopia became more arid after Toba, it is less clear whether local temperatures became cooler. And while Toba did cause some climate changes in Africa, it does not appear that humans there came close to extinction as a result.

“I think it’s a really nice example of how science works,” Kappelman says. “Theories get proposed. We go out, we collect data to test that theory. And the theory can be revised or—in some cases like this one, at least with regard to the African populations—really shown to not have very much strength to it.”