The Toba supereruption (Youngest Toba Tuff or simply YTT[1]) was a supervolcanic eruption that occurred sometime between 69,000 and 77,000 years ago at Lake Toba (Sumatra, Indonesia). It is recognized as one of the Earth's largest known eruptions. The related catastrophe hypothesis holds that this event caused a global volcanic winter of 6–10 years and possibly a 1,000-year-long cooling episode.

The Toba event is the most closely studied supereruption. In 1993, science journalist Ann Gibbons suggested a link between the eruption and a bottleneck in human evolution, and Michael R. Rampino of New York University and Stephen Self of the University of Hawaii at Manoa gave support to the idea. In 1998, the bottleneck theory was further developed by Stanley H. Ambrose of the University of Illinois at Urbana-Champaign. Other researchers have questioned or found no evidence for a link between the Toba eruption and such bottleneck.

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