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The Youngest Toba eruption was a
supervolcano A supervolcano is a volcano that has had an eruption with a Volcanic Explosivity Index (VEI) of 8, the largest recorded value on the index. This means the volume of deposits for such an eruption is greater than 1,000 cubic kilometers (240 cubi ...
eruption Several types of volcanic eruptions—during which lava, tephra (Volcanic ash, ash, lapilli, volcanic bombs and volcanic blocks), and Volcanic gas, assorted gases are expelled from a Volcano, volcanic vent or fissure vent, fissure—have been ...
that occurred around 74,000 years ago at the site of present-day
Lake Toba Lake Toba ( id, Danau Toba) ( Toba Batak: ᯖᯀᯬ ᯖᯬᯅ; romanized: ''Tao Toba'') is a large natural lake in North Sumatra, Indonesia, occupying the caldera of a supervolcano. The lake is located in the middle of the northern part of the i ...
in
Sumatra Sumatra is one of the Sunda Islands of western Indonesia. It is the largest island that is fully within Indonesian territory, as well as the sixth-largest island in the world at 473,481 km2 (182,812 mi.2), not including adjacent is ...
,
Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guine ...
. It is one of the
Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
's largest known explosive eruptions. The Toba catastrophe theory holds that this event caused a global
volcanic winter A volcanic winter is a reduction in global temperatures caused by volcanic ash and droplets of sulfuric acid and water obscuring the Sun and raising Earth's albedo (increasing the reflection of solar radiation) after a large, particularly explosiv ...
of six to ten years and possibly a 1,000-year-long cooling episode. In 1993, science journalist Ann Gibbons posited that a
population bottleneck A population bottleneck or genetic bottleneck is a sharp reduction in the size of a population due to environmental events such as famines, earthquakes, floods, fires, disease, and droughts; or human activities such as specicide, widespread violen ...
occurred in human
evolution Evolution is change in the heredity, heritable Phenotypic trait, characteristics of biological populations over successive generations. These characteristics are the Gene expression, expressions of genes, which are passed on from parent to ...
about 70,000 years ago, and she suggested that this was caused by the eruption. Geologist Michael R. Rampino of
New York University New York University (NYU) is a private research university in New York City. Chartered in 1831 by the New York State Legislature, NYU was founded by a group of New Yorkers led by then-Secretary of the Treasury Albert Gallatin. In 1832, t ...
and volcanologist Stephen Self of the
University of Hawaiʻi at Mānoa The University of Hawaii at Mānoa (University of Hawaii—Mānoa, UH Mānoa, Hawai'i, or simply UH) is a public land-grant research university in Mānoa, a neighborhood in Honolulu, Hawaii. It is the flagship campus of the University of Haw ...
support her suggestion. In 1998, the bottleneck theory was further developed by anthropologist Stanley H. Ambrose of the
University of Illinois Urbana-Champaign The University of Illinois Urbana-Champaign (U of I, Illinois, University of Illinois, or UIUC) is a public land-grant research university in Illinois in the twin cities of Champaign and Urbana. It is the flagship institution of the Universi ...
. Both the link and global winter theories are controversial. The Youngest Toba eruption is the most closely studied supervolcanic eruption.


Supervolcanic eruption

The Youngest Toba eruption occurred at the present location of
Lake Toba Lake Toba ( id, Danau Toba) ( Toba Batak: ᯖᯀᯬ ᯖᯬᯅ; romanized: ''Tao Toba'') is a large natural lake in North Sumatra, Indonesia, occupying the caldera of a supervolcano. The lake is located in the middle of the northern part of the i ...
in
Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guine ...
, about 74,000 years BP according to potassium argon dating. This eruption was the last and largest of four eruptions of the Toba Caldera Complex during the
Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million yea ...
period, and is also recognized from its diagnostic horizon of ashfall, the Youngest Toba
tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock ...
. It had an estimated Volcanic Explosivity Index (VEI) of 8 (the highest rating on the scale); it made a sizable contribution to the
caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcano eruption. When large volumes of magma are erupted over a short time, structural support for the rock above the magma chamber is ...
complex. Dense-rock equivalent (DRE) estimates of eruptive volume for the eruption vary between and ; the most common DRE estimate is of about of erupted magma, of which was deposited as ash fall. The erupted mass was, at the very least, 12 times greater than that of the largest volcanic eruption in recent history, the 1815 eruption of
Mount Tambora Mount Tambora, or Tomboro, is an active stratovolcano in West Nusa Tenggara, Indonesia. Located on Sumbawa in the Lesser Sunda Islands, it was formed by the active subduction zones beneath it. Before 1815, its elevation reached more than high ...
in Indonesia, which caused the 1816 "
Year Without a Summer The year 1816 is known as the Year Without a Summer because of severe climate abnormalities that caused average global temperatures to decrease by . Summer temperatures in Europe were the coldest on record between the years of 1766–2000. Thi ...
" in the Northern Hemisphere. Toba's erupted mass deposited an ash layer of about thick over the whole of
South Asia South Asia is the southern subregion of Asia, which is defined in both geographical and ethno-cultural terms. The region consists of the countries of Afghanistan, Bangladesh, Bhutan, India, Maldives, Nepal, Pakistan, and Sri Lanka. ...
. A blanket of volcanic ash was also deposited over the
Indian Ocean The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or ~19.8% of the water on Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia to the east. To the south it is bounded by ...
, the
Arabian Sea The Arabian Sea ( ar, اَلْبَحرْ ٱلْعَرَبِيُّ, Al-Bahr al-ˁArabī) is a region of the northern Indian Ocean bounded on the north by Pakistan, Iran and the Gulf of Oman, on the west by the Gulf of Aden, Guardafui Channel ...
, and the
South China Sea The South China Sea is a marginal sea of the Western Pacific Ocean. It is bounded in the north by the shores of South China (hence the name), in the west by the Indochinese Peninsula, in the east by the islands of Taiwan and northwestern P ...
. Deep-sea cores retrieved from the South China Sea have extended the known reach of the eruption, suggesting that the calculation of the erupted mass is a minimum value or even an underestimate. Based on new methods (computational ash dispersal model using a 3D time-dependent tephra dispersion model, a set of wind fields, and several tens of thickness measurements of the YTT tephra deposit), the Toba Caldera Complex possibly erupted as much as in total bulk volume. This has led to some sources labelling the Youngest Toba eruption as a "VEI-9" event.


Volcanic winter and global cooling computer models

Geologist Michael R. Rampino and volcanologist Stephen Self argue that the eruption caused a "brief, dramatic cooling or '
volcanic winter A volcanic winter is a reduction in global temperatures caused by volcanic ash and droplets of sulfuric acid and water obscuring the Sun and raising Earth's albedo (increasing the reflection of solar radiation) after a large, particularly explosiv ...
, which resulted in a drop of the global mean surface temperature by . Evidence from
Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland is ...
ice core An ice core is a core sample that is typically removed from an ice sheet or a high mountain glacier. Since the ice forms from the incremental buildup of annual layers of snow, lower layers are older than upper ones, and an ice core contains ...
s indicates a 1,000-year period of low ''δ''18O and increased dust deposition immediately following the eruption. The eruption may have caused this 1,000-year period of cooler temperatures (stadial), two centuries of which could be accounted for by the persistence of the Toba stratospheric loading. Rampino and Self believe that
global cooling Global cooling was a conjecture, especially during the 1970s, of imminent cooling of the Earth culminating in a period of extensive glaciation, due to the cooling effects of aerosols or orbital forcing. Some press reports in the 1970s specul ...
was already underway at the time of the eruption, but that the process was slow; the Youngest Toba
tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock ...
"may have provided the extra 'kick' that caused the climate system to switch from warm to cold states". Although Clive Oppenheimer rejects the hypothesis that the eruption triggered the last glaciation, he agrees that it may have been responsible for a millennium of cool climate prior to the 19th
Dansgaard–Oeschger event Dansgaard–Oeschger events (often abbreviated D–O events), named after palaeoclimatologists Willi Dansgaard and Hans Oeschger, are rapid climate fluctuations that occurred 25 times during the last glacial period. Some scientists say that th ...
. According to
Alan Robock Alan may refer to: People *Alan (surname), an English and Turkish surname *Alan (given name), an English given name ** List of people with given name Alan ''Following are people commonly referred to solely by "Alan" or by a homonymous name.'' * ...
, who has also published
nuclear winter Nuclear winter is a severe and prolonged global climatic cooling effect that is hypothesized to occur after widespread firestorms following a large-scale nuclear war. The hypothesis is based on the fact that such fires can inject soot into th ...
papers, the Toba eruption did not precipitate the last glacial period. However, assuming an emission of of
sulphur dioxide Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a toxic gas responsible for the odor of burnt matches. It is released naturally by volcanic ac ...
, his computer simulations concluded that a maximum global cooling of approximately occurred for three years after the eruption, and that this cooling would last for decades, devastating life.. Because the saturated
adiabatic lapse rate The lapse rate is the rate at which an atmospheric variable, normally temperature in Earth's atmosphere, falls with altitude. ''Lapse rate'' arises from the word ''lapse'', in the sense of a gradual fall. In dry air, the adiabatic lapse rate is ...
is 4.9 °C/1,000 m (1.5 °C/1,000 ft; 2.7 °F/1,000 ft) for temperatures above freezing, the
tree line The tree line is the edge of the habitat at which trees are capable of growing. It is found at high elevations and high latitudes. Beyond the tree line, trees cannot tolerate the environmental conditions (usually cold temperatures, extreme snowp ...
and the
snow line The climatic snow line is the boundary between a snow-covered and snow-free surface. The actual snow line may adjust seasonally, and be either significantly higher in elevation, or lower. The permanent snow line is the level above which snow wi ...
were around lower at this time. The climate recovered over a few decades, and Robock found no evidence that the 1,000-year cold period seen in Greenland ice core records had resulted from the Toba eruption. In contrast, Oppenheimer believes that estimates of a drop in surface temperature by are probably too high, and he suggests that temperatures dropped only by . Robock has criticized Oppenheimer's analysis, arguing that it is based on simplistic T-forcing relationships. Despite these different estimates, scientists agree that a supervolcanic eruption of the scale at the Toba Caldera Complex must have led to very extensive ash-fall layers and injection of noxious gases into the atmosphere, with worldwide effects on weather and climate. In addition, the Greenland ice core data display an abrupt climate change around this time, but there is no consensus that the eruption directly generated the 1,000-year cold period seen in Greenland or triggered the last glaciation.


Physical data against the winter hypothesis

In 2013 archaeologists led by Christine Lane reported finding a microscopic layer of glassy volcanic ash in sediments of
Lake Malawi Lake Malawi, also known as Lake Nyasa in Tanzania and Lago Niassa in Mozambique, is an African Great Lake and the southernmost lake in the East African Rift system, located between Malawi, Mozambique and Tanzania. It is the fifth largest fre ...
, and definitively linked the ash to the 75,000-year-old eruption at the Toba Caldera Complex, but found no change in fossil type close to the ash layer, something that would be expected following a severe
volcanic winter A volcanic winter is a reduction in global temperatures caused by volcanic ash and droplets of sulfuric acid and water obscuring the Sun and raising Earth's albedo (increasing the reflection of solar radiation) after a large, particularly explosiv ...
. They concluded that the eruption did not significantly alter the climate of East Africa, attracting criticism from Richard Roberts. Lane explained, "We examined smear slides at a interval, corresponding to subdecadal resolution, and X-ray fluorescence scans run at intervals correspond to subannual resolution. We observed no obvious change in sediment composition or Fe/Ti ratio, suggesting that no thermally driven overturn of the water column occurred following the Toba supereruption." In 2015, a new study on the climate of East Africa supported Lane's conclusion that there was "no significant cooling associated with Mount Toba". A 2018 study by Chad Yost and colleagues of cores from Lake Malawi dating to the period of the Youngest Toba eruption showed no evidence of a volcanic winter, and they argue that there was no effect on African humans. In the view of John Hawks, the study confirms evidence from a variety of studies that the eruption did not have a major climatic effect or any effect on human numbers.


Genetic bottleneck hypothesis


Genetic bottleneck in humans

The Youngest Toba eruption has been linked to a genetic bottleneck in human evolution about 70,000 years ago; it is hypothesized that the eruption resulted in a severe reduction in the size of the total human population due to the effects of the eruption on the global climate. According to the genetic bottleneck theory, between 50,000 and 100,000 years ago, human populations sharply decreased to 3,000–10,000 surviving individuals. It is supported by some genetic evidence suggesting that today's humans are descended from a very small population of between 1,000 and 10,000 breeding pairs that existed about 70,000 years ago. Proponents of the genetic bottleneck theory (including Robock) suggest that the Youngest Toba eruption resulted in a global ecological disaster, including destruction of vegetation along with severe drought in the
tropical rainforest Tropical rainforests are rainforests that occur in areas of tropical rainforest climate in which there is no dry season – all months have an average precipitation of at least 60 mm – and may also be referred to as ''lowland equat ...
belt and in monsoonal regions. A 10-year volcanic winter triggered by the eruption could have largely destroyed the food sources of humans and caused a severe reduction in population sizes. These environmental changes may have generated population bottlenecks in many species, including
hominid The Hominidae (), whose members are known as the great apes or hominids (), are a taxonomic family of primates that includes eight extant species in four genera: '' Pongo'' (the Bornean, Sumatran and Tapanuli orangutan); '' Gorilla'' (th ...
s; this in turn may have accelerated differentiation from within the smaller human population. Therefore, the genetic differences among modern humans may reflect changes within the last 70,000 years, rather than gradual differentiation over hundreds of thousands of years. Other research has cast doubt on a link between the Toba Caldera Complex and a genetic bottleneck. For example, ancient
stone tool A stone tool is, in the most general sense, any tool made either partially or entirely out of stone. Although stone tool-dependent societies and cultures still exist today, most stone tools are associated with prehistoric (particularly Stone Ag ...
s in southern India were found above and below a thick layer of ash from the Youngest Toba eruption and were very similar across these layers, suggesting that the dust clouds from the eruption did not wipe out this local population. Additional archaeological evidence from southern and northern India also suggests a lack of evidence for effects of the eruption on local populations, leading the authors of the study to conclude, "many forms of life survived the supereruption, contrary to other research which has suggested significant animal extinctions and genetic bottlenecks". However, evidence from pollen analysis has suggested prolonged deforestation in South Asia, and some researchers have suggested that the Toba eruption may have forced humans to adopt new adaptive strategies, which may have permitted them to replace
Neanderthal Neanderthals (, also ''Homo neanderthalensis'' and erroneously ''Homo sapiens neanderthalensis''), also written as Neandertals, are an extinct species or subspecies of archaic humans who lived in Eurasia until about 40,000 years ago. While the ...
s and "other archaic human species". Additional caveats include difficulties in estimating the global and regional climatic impacts of the eruption and lack of conclusive evidence for the eruption preceding the bottleneck. Furthermore, genetic analysis of
Alu sequence An Alu element is a short stretch of DNA originally characterized by the action of the ''Arthrobacter luteus (Alu)'' restriction endonuclease. ''Alu'' elements are the most abundant transposable elements, containing over one million copies di ...
s across the entire
human genome The human genome is a complete set of nucleic acid sequences for humans, encoded as DNA within the 23 chromosome pairs in cell nuclei and in a small DNA molecule found within individual mitochondria. These are usually treated separately as the ...
has shown that the effective human population size was less than 26,000 at 1.2 million years ago; possible explanations for the low population size of human ancestors may include repeated population bottlenecks or periodic replacement events from competing ''
Homo ''Homo'' () is the genus that emerged in the (otherwise extinct) genus ''Australopithecus'' that encompasses the extant species ''Homo sapiens'' (modern humans), plus several extinct species classified as either ancestral to or closely related ...
'' subspecies.


Genetic bottlenecks in other mammals

Some evidence points to genetic bottlenecks in other animals in the wake of the Youngest Toba eruption. The populations of the Eastern African
chimpanzee The chimpanzee (''Pan troglodytes''), also known as simply the chimp, is a species of great ape native to the forest and savannah of tropical Africa. It has four confirmed subspecies and a fifth proposed subspecies. When its close relative th ...
,
Bornean orangutan The Bornean orangutan (''Pongo pygmaeus'') is a species of orangutan endemic to the island of Borneo. Together with the Sumatran orangutan (''Pongo abelii'') and Tapanuli orangutan (''Pongo tapanuliensis''), it belongs to the only genus of grea ...
, central Indian
macaque The macaques () constitute a genus (''Macaca'') of gregarious Old World monkeys of the subfamily Cercopithecinae. The 23 species of macaques inhabit ranges throughout Asia, North Africa, and (in one instance) Gibraltar. Macaques are principal ...
,
cheetah The cheetah (''Acinonyx jubatus'') is a large cat native to Africa and central Iran. It is the fastest land animal, estimated to be capable of running at with the fastest reliably recorded speeds being , and as such has evolved specialize ...
and
tiger The tiger (''Panthera tigris'') is the largest living Felidae, cat species and a member of the genus ''Panthera''. It is most recognisable for its dark vertical stripes on orange fur with a white underside. An apex predator, it primarily pr ...
, all recovered from very small populations around 70,000–55,000 years ago.


Migration after Toba

The exact geographic distribution of anatomically modern human populations at the time of the eruption is not known, and surviving populations may have lived in
Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
and subsequently migrated to other parts of the world. Analyses of
mitochondrial DNA Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). Mitochondrial DN ...
have estimated that the major migration from Africa occurred 60,000–70,000 years ago, consistent with dating of the Youngest Toba eruption to around 75,000 years ago.


See also

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Citations and notes


References

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Further reading

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External links


Population Bottlenecks and Volcanic Winter
*
"The proper study of mankind"
– Article in ''
The Economist ''The Economist'' is a British weekly newspaper printed in demitab format and published digitally. It focuses on current affairs, international business, politics, technology, and culture. Based in London, the newspaper is owned by The Econ ...
''
Homepage of Professor Stanley H. Ambrose
including bibliographic informatio on the two papers he has published on the Toba catastrophe theory

ScienceDaily (Sep. 8, 1998) – Article based on news release regarding Ambrose's paper
Mount Toba: Late Pleistocene human population bottlenecks, volcanic winter, and differentiation of modern humans
by Professor Stanley H. Ambrose, Department of Anthropology, University Of Illinois, Urbana, USA; Extract from "Journal of Human Evolution" 99834, 623–651
Journey of Mankind
by The Bradshaw Foundation – includes discussion on Toba eruption, DNA and human migrations

ScienceDaily (Mar. 17, 2005) – By analyzing the relationship between the geographic location of current human populations in relation to East Africa and the genetic variability within these populations, researchers have found new evidence for an African origin of modern humans.

ScienceDaily (Feb. 16, 2007) – When man made his way out of Africa some 60,000 years ago to populate the world, he was not alone: He was accompanied by the bacterium
Helicobacter pylori ''Helicobacter pylori'', previously known as ''Campylobacter pylori'', is a gram-negative, microaerophilic, spiral (helical) bacterium usually found in the stomach. Its helical shape (from which the genus name, helicobacter, derives) is thoug ...
...; illus. migration map.
Magma 'Pancakes' May Have Fueled Toba Supervolcano

Youtube video "Stone Age Apocalypse"
{{DEFAULTSORT:Toba Catastrophe Theory Scientific theories Extinction events Geology theories Human evolution Lake Toba Prehistoric Indonesia Pre-Holocene volcanism Supervolcanoes Ancient natural disasters Pleistocene volcanism Events that forced the climate VEI-8 eruptions Volcanic eruptions in Indonesia Volcanic winters