Around 74,000 years ago, a volcano on what is now Sumatra erupted with a force roughly 1,000 times greater than Mount Pinatubo in 1991. Mount Toba ejected thousands of cubic kilometers of magma in about two weeks, making it the largest volcanic eruption in the last 2.6 million years. For years, some scientists believed it nearly wiped out early humans. New research suggests it did not come close.
According to Ars Technica, a team of geoscientists found that the eruption caused less than half a degree of cooling and that its climate effects lasted under two years. Their evidence came from mud pulled out of a small crater lake on the Kenya-Tanzania border.
Jinheum Park, a geoscientist at Johannes Gutenberg University in Mainz, Germany, led the research. He and his colleagues were looking for signs of the volcanic catastrophe preserved in lake sediments.
"People thought it might have caused massive cooling of the planet, and hence threatened the survival of our ancestors," Park said.
What they found told a different story.
Volcanic eruptions push sulfur dioxide into the stratosphere, where it forms a haze of tiny droplets that reflect sunlight back into space. Larger eruptions generally mean more sulfur dioxide and more cooling. But that relationship breaks down beyond a certain size.
"Bigger sulfate aerosols settle quickly, because they are heavier," Park explained. When aerosols are too large, they fall out of the stratosphere faster and scatter less sunlight. That physical limit may have capped how much cooling Toba could actually produce, no matter how large the eruption was.
Earlier estimates of Toba's sulfur output varied so widely that computer models produced results ranging from near-extinction conditions to a minor inconvenience. To get a more reliable answer, scientists turned to geological records, specifically ash layers preserved in seafloor and lake cores. That approach also had problems.
Sediment cores taken from underwater environments typically blur short, violent events. When material settles to the bottom of a lake or ocean, deposits from different years mix together. Even thin slices of a mud core reflect years of mixed climate signals. A volcanic winter lasting one to three years would be difficult to detect in most such records.
The crater lake Park's team studied was different. Its sediment layers were distinct enough to capture short-term climate changes, allowing the team to isolate the Toba signal and measure its duration and intensity with more precision than previous studies had managed.
The result: an eruption that was geologically spectacular but climatically brief, one that did not produce the kind of sustained cooling that would have pushed early human populations toward extinction.
