A new paper by Martin A.J. Williams et al, on the Mount Toba eruption 73,000 years ago, proposes that the destructive aftermath of the event caused widespread de-forestation in India, some 3,000 miles distant from Sumatra, the island on which the volcano was located. Here’s the abstract of that paper which is behind a paywall, but commented upon in Science Daily, to which I’ll refer shortly:


The cooling effects of historic volcanic eruptions on world climate are well known but the impacts of even bigger prehistoric eruptions are still shrouded in mystery. The eruption of Toba volcano in northern Sumatra some 73,000 years ago was the largest explosive eruption of the past two million years, with a Volcanic Explosivity Index of magnitude 8, but its impact on climate has been controversial. In order to resolve this issue, we have analysed pollen from a marine core in the Bay of Bengal with stratified Toba ash, and the carbon isotopic composition of soil carbonates directly above and below the ash in three sites on a 400 km transect across central India.

Pollen evidence shows that the eruption was followed by initial cooling and prolonged desiccation, reflected in a decline in tree cover in India and the adjacent region. Carbon isotopes show that C3 forest was replaced by wooded to open C4 grassland in central India. Our results demonstrate that the Toba eruption caused climatic cooling and prolonged deforestation in South Asia, and challenge claims of minimal impact on tropical ecosystems and human populations.

The story is taken up by Science Daily,  in Supervolcano Eruption In Sumatra Deforested India 73,000 Years Ago, where the sheer scale of the event is reflected in this description of the eruption and the site itself:

The volcano ejected an estimated 800 cubic kilometers of ash into the atmosphere, leaving a crater (now the world’s largest volcanic lake) that is 100 kilometers long and 35 kilometers wide. Ash from the event has been found in India, the Indian Ocean, the Bay of Bengal and the South China Sea.

The bright ash reflected sunlight off the landscape, and volcanic sulfur aerosols impeded solar radiation for six years, initiating an “Instant Ice Age” that — according to evidence in ice cores taken in Greenland — lasted about 1,800 years.

During this instant ice age, temperatures dropped by as much as 16 degrees centigrade (28 degrees Fahrenheit), said University of Illinois anthropology professor Stanley Ambrose, a principal investigator on the new study with professor Martin A.J. Williams, of the University of Adelaide. Williams, who discovered a layer of Toba ash in central India in 1980, led the research.

The report then goes on to comment on the debate that has sprung up surrounding the idea that this event nearly wiped humanity off the face of the planet, causing a putative genetic ‘bottleneck’ event, whereby the diversity of the human gene pool was dramatically reduced, prompting some researchers to contend that the anatomically modern human population immediately after Mount Toba may have numbered only about 15,000 individuals. This idea has however been contested, most notably in a 2007 paper by Michael Petraglia et al, in which it is suggested that Middle Palaeolithic technology appears to have continued across the region without significant interruption, following investigations at the site of Jwalapuram.

The Science Daily report also gives details of how Williams and his team were able to deduce the climatic impact of the eruption, as we see from this:

To address the limited evidence of the terrestrial effects of Toba, Ambrose and his colleagues pursued two lines of research: They analyzed pollen from a marine core in the Bay of Bengal that included a layer of ash from the Toba eruption, and they looked at carbon isotope ratios in fossil soil carbonates taken from directly above and below the Toba ash in three locations in central India.

Carbon isotopes reflect the type of vegetation that existed at a given locale and time. Heavily forested regions leave carbon isotope fingerprints that are distinct from those of grasses or grassy woodlands.

Both lines of evidence revealed a distinct change in the type of vegetation in India immediately after the Toba eruption, the researchers report. The pollen analysis indicated a shift to a “more open vegetation cover and reduced representation of ferns, particularly in the first 5 to 7 centimeters above the Toba ash,” they wrote in the journal Palaeogeography, Palaeoclimatology, Palaeoecology. The change in vegetation and the loss of ferns, which grow best in humid conditions, they wrote, “would suggest significantly drier conditions in this region for at least one thousand years after the Toba eruption.”

The dryness probably also indicates a drop in temperature, Ambrose said, “because when you turn down the temperature you also turn down the rainfall.”

The carbon isotope analysis showed that forests covered central India when the eruption occurred, but wooded to open grassland predominated for at least 1,000 years after the eruption.

“This is unambiguous evidence that Toba caused deforestation in the tropics for a long time,” Ambrose said.

This disaster may have forced the ancestors of modern humans to adopt new cooperative strategies for survival that eventually permitted them to replace Neandertals and other archaic human species, he said.

That last sentence regarding Neanderthal extinction seems to me to be stretching a point, especially when we bear in mind that Neanderthals survived Mount Toba by around 50,000 years, and there is nothing specific in the archaeological record that points to sudden innovations by AMH at this time. Even if we take into account the findings at Blombos for example, where it was originally proposed that the first modern human attempts at creating art were made, around 77,000 years bp, and subsequently at several even earlier sites in North Africa, it is clear that the path, or at least a side-road of that path to so-called modernity had been embarked upon prior to the eruption. It is notable howeverthat this particular mode of behaviour seems to disappear until modern humans made their mark in Upper Palaeolithic Europe around 42,000 bp.

To demonstrate that AMH would have changed the way in which they made a living to the extent that it gave them some sort of killer advantage would require a more exhaustive analysis on floral and faunal populations as well – obviously prey species would have been affected by the eruption, but whether entire species were wiped out causing AMH to adopt different food hunting and gathering methods is an open question. It seems parsimonious to suggest that a reduced human population would have been able to survive on a reduced (but not extinct) prey population, meaning that supply would still have roughly matched demand, and that no large changes in material culture would have been necessary.

What we don’t know of course is the impact the Toba eruption might have had on the mindsets of both AMH and Neanderthals who may have occupied the region,  and maybe late-surviving H. erectus, all of whom would no doubt have been awed by the sheer magnitude and extent of the destruction visited upon their world; titanic explosions that rained down debris from the sky, causing rapid deterioration of climate and associated habitats could well have spawned thoughts that the world was coming to an end, though whether such disasters were routinely ascribed to the natural world or some kind of divine or hellish intervention, is again, an unknown.

However, there is one location in Africa, and dated to 70,000 bp, that might offer an intriguing hint that some kind of behaviour linked to abstract belief through use of ritualistic symbolism in the guise of destruction, was present at this early date. The 2006 report, again from Science Daily, World’s Oldest Ritual Discovered Worshipped The Python 70,000 Years Ago documents a discovery by Associate Professor Sheila Coulson, from the University of Oslo, which describes what might be the earliest known example of the ritual destruction of humanly crafted objects, in this case, red spear-points, that were fashioned from stones sourced from hundreds of kilometres away from the Tsodilo Hills, site of the cave, described in part here:

“Stone age people took these colourful spearheads, brought them to the cave, and finished carving them there. Only the red spearheads were burned. It was a ritual destruction of artifacts. There was no sign of normal habitation. No ordinary tools were found at the site. Our find means that humans were more organised and had the capacity for abstract thinking at a much earlier point in history than we have previously assumed. All of the indications suggest that Tsodilo has been known to mankind for almost 100,000 years as a very special place in the pre-historic landscape.” says Sheila Coulson.

Sheila Coulson also noticed a secret chamber behind the python stone. Some areas of the entrance to this small chamber were worn smooth, indicating that many people had passed through it over the years.

Ostensibly there’s nothing to suggest that the human activities in this cave of the python were directly or even indirectly influenced by the Mount Toba eruption thousands of miles away, and indeed the dates for both the eruption and ritual activity in the African cave aren’t exact, but assuming Toba was the preceding event, it would be interesting to know if, when and to what extent news of Toba reached ancient African ears, and exactly how the eruption and ensuing catastrophic decline in environment and climate may have been reported and interpreted.

via Gene Expression

image: Landsat satellite photo of Lake Toba, Sumatra, Indonesia. (Credit: Image courtesy of NASA / via Wikimedia Commons)


Environmental Impact of the 73 ka Toba super-eruption in South Asia, Article in Press, Corrected Proof , by Martin A.J. Williams , Stanley H. Ambrose, Sander van der Kaars, Carsten Ruehlemann, Umesh Chattopadhyaya, Jagannath Pal and Parth R. Chauhan, doi:10.1016/j.palaeo.2009.10.009

Middle Paleolithic Assemblages from the Indian Subcontinent Before and After the Toba Super-Eruption, by Michael Petraglia et al, Science 6 July 2007: Vol. 317. no. 5834, pp. 114 – 116 DOI: 10.1126/science.1141564