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Toba supereruption
c. 74,000 years ago; effects debated· Event· Earth, climate & extinctions
DebatedScientists disagree about when, how or why.
A colossal volcanic eruption in Sumatra about 74,000 years ago, the largest known in the last two million years.
See it on the Life map →What happened
Toba ejected roughly 2,800 cubic kilometers of rock and ash, thousands of times more than Mount St. Helens in 1980, and left a caldera now filled by Lake Toba, about 100 km long. Ash blanketed South Asia, and microscopic glass shards reached Africa. In 1998, the 'Toba catastrophe' hypothesis proposed that it caused a volcanic winter that nearly wiped out humanity. Most evidence gathered since then argues against such a severe effect.
Why it matters
It is a natural test of how a supereruption affects climate and people, and the evidence so far suggests early humans proved resilient.
The evidence (fossils, genes, rocks)
Argon–argon dating of the ash; ash layers in ocean and lake cores; and archaeological sites in India, South Africa and Ethiopia with tools both below and above the ash.
Still debated
How much and for how long global temperatures dropped, and whether the eruption affected human populations or migrations at all.
Connections (2)
▸Toba supereruption may have affected Out of Africa: Homo sapiens spreads worldwideDebated
The connection
In 1998, anthropologist Stanley Ambrose proposed that Toba's 'volcanic winter' cut human numbers to a few thousand, explaining our low genetic diversity and setting up the later dispersal. Newer evidence shows people in Africa and India came through the eruption, and may even have spread out afterward along seasonal rivers.
When and how
Sumatra, Indonesia, about 74,000 years ago; ash studied at Jwalapuram (India), Pinnacle Point (South Africa) and Shinfa-Metema 1 (Ethiopia).
How sure are we?
Tiny Toba glass shards at African and Indian sites show people living through the eruption; Lake Malawi cores show no severe cooling there.
Debates and open questions
Whether Toba affected the timing of dispersals at all is unclear. Genetic bottlenecks are now usually explained by the founder effect of small migrating groups.
▸Toba supereruption may have deepened the cold of Pleistocene ice agesDebated
The connection
Toba blasted sulfur gases into the stratosphere, forming a haze that reflects sunlight. Climate models suggest a few years of sharp global cooling. It erupted as the last ice age was turning colder, and some researchers proposed it helped tip climate into a colder phase.
When and how
About 74,000 years ago, near the shift into a cold glacial stage (Marine Isotope Stage 4); ash fell from the South China Sea to southern Africa.
How sure are we?
Greenland and Antarctic ice cores record large sulfate spikes near that date, but pinning a particular spike on Toba is difficult.
Debates and open questions
Model estimates of the cooling range from mild to severe. Most researchers doubt it changed the long-term ice-age trend, which orbital cycles drove.