Did the Mount Toba Eruption Almost Wipe Out Humans?
According to BBC News, “The ‘super-eruption’ of Mount Toba on the Indonesian island of Sumatra is thought by some to have caused a six-year long volcanic winter followed by a 1,000-year-long freeze.”
The World’s Biggest Volcanic Eruption
Everything about the eruption of Mount Toba challenges the human mind. It is given an eight on the Volcanic Explosivity Index; that’s the highest rating possible. For comparison, when Mount St. Helens blew its top in May 1980, it was given a rating of five.
However, the Index is logarithmic, meaning that Toba’s eruption was several thousand times bigger than that of Mount St. Helens.
Volcanologists describe the Mount Toba event as “mega-colossal,” chucking out somewhere around 2,800 cubic kilometres of debris. When it settled back down it covered the ground in a layer of ash over South Asia, the Indian Ocean, and the Arabian and South China Seas. This layer can still be seen.
Another measure of the scale of this eruption is that Mount Toba is now Lake Toba, a body of water 100 km long, 30 km wide, and more than 500 metres at its deepest.
India Takes a Direct Hit
At the Bradshaw Foundation, Stephen Oppenheimer provides an account of the aftermath of Mount Toba’s huge rumble: “This mega-bang caused a prolonged world-wide nuclear winter and released ash in a huge plume that spread to the north-west and covered India, Pakistan, and the Gulf region in a blanket 1–5 metres (3–15 feet) deep.”
India was in the direct line of fire and may have suffered a mass extinction of human and other life. Oppenheimer suggests nobody on the Indian subcontinent would have survived the cataclysm.
Mount Toba’s Ash Went Global
In a program aired on the Australian Broadcasting Corporation Science Show, Martin Williams, an emeritus professor at the University of Adelaide, spoke about the worldwide impact of the explosion.
The ash and sulphur suspended in the atmosphere filtered out sunlight and caused a dramatic and catastrophic change in climate: “… in Greenland associated with it you have a 16-degree drop in temperature, which is quite dramatic ...”
It’s been estimated that this plunge in temperatures killed off three quarters of the plant life in the Northern Hemisphere with equally catastrophic impacts in the southern half of the planet. It didn’t help that the Earth was going through one of its periodic ice ages.
It was at least six years before the Sun’s life-giving heat and light reached their normal intensity. This disrupted weather patterns such as seasonal rains causing plants bearing berries and nuts to die and game animal populations to plunge. Humans starved.
Human Population Bottleneck
The loss of vegetation meant a shortage of food for all animals, including humans, and a resulting famine. This prompted anthropologist Stanley Ambrose of the University of Illinois to advance the notion that the human population came close to extinction in the aftermath of the Mount Toba eruption.
Geneticists have known for some time there was a population “bottleneck” during which the number of humans declined rapidly. According to Dr. David Whitehouse, BBC News science editor “Some scientists estimate that there may have been as few as 15,000 humans alive at one time … The rapid decrease, in our ancestors’ populations, in turn, brought about the rapid differentiation - or genetic divergence - of the surviving populations.”
Robert Krulwich of National Public Radio reviewed the literature and wrote “the world-wide population of human beings skidded so sharply we were down to roughly a thousand reproductive adults. One study says we hit as low as 40.”
He concludes the number 40 is a bit far-fetched and suggests the total world population settled to between 5,000 and 10,000. He quotes science writer Sam Kean as saying “We damn near went extinct.”
Mount St. Helens Was Puny Compared to Mount Toba
Challenge to Near-Extinction Theory
But, other scientists challenge the notion that humans nearly vanished. Back at the ABC Science Show, Dr. Martin Williams says “One school says there was no impact whatsoever because when you look at the artifacts in southern India above and beneath the ash they’re the same, they’re … middle stone age, therefore no impact.”
This is confirmed by a report in the Sydney Morning Herald written by Science Editor Deborah Smith: “Hundreds of sophisticated stone tools have been found in Jwalapuram in southern India by an international team including two Australian researchers, Chris Clarkson and Bert Roberts.”
This is taken as tentative proof that at least some people in India survived the after effects of Mount Toba’s bout of seismic indigestion, although Clarkson and Roberts are quick to point out more research is needed.
When Mount Tambora exploded in Indonesia in 1816 it caused a “Year Without a Summer” in the Northern Hemisphere. Mount Toba’s eruption was 100 times greater than this.
Here’s a cheery thought: Mount Toba may erupt again. Indonesia Geological Experts Association president Rovicky Dwi Putrohari says although the mountain disappeared 74,000 years its magma chamber remains intact. Researchers have located this large pool of pressurized liquid rock at between 20 and 100 kilometres below the surface.
According to The National Geographic, Mount Toba’s big bang created enough lava to build two Mount Everests.
Some animals, dogs in particular, are thought to be able to detect infrasounds that give warning of an impending natural disaster such as a volcanic eruption, earthquake, or tsunami. These are noises that are inaudible to humans. Another theory is that some animals are sensitive to changes in electromagnetic fields that may presage a disaster.
About 80 percent of the world’s land surface was created by volcanic action and today more than 500 volcanoes remain active.
Mount Toba is Missing from This List
- “How Volcanoes Have Shaped History.” BBC News April 15, 2010 Bernard Gagnon
- “Ancient ‘Volcanic Winter’ Tied to Rapid Genetic Divergence in Humans.” ScienceDaily, September 8, 1998.
- “Humans Came ‘Close to Extinction.’ ” Dr. David Whitehouse, BBC News, September 8, 1998.
- “Volcano May not Have Blown it.” Deborah Smith, Sydney Morning Herald, July 23, 2007.
- “How Human Beings Almost Vanished From Earth In 70,000 B.C.” Robert Krulwich, National Public Radio, October 22, 2012.
- “North Sumatra’s Mount Toba May Erupt Again, at any Time.” Apriadi Gunawan, The Jakarta Post, November 4, 2013.