TOBA SUPERVOLCANO ERUPTION
The single worst explosion in our geological history occurred at Lake Toba, about 160 kilometers from the epicenter of the 2004 tsunami-producing earthquake. It occurred 71,000 year ago and produced a caldera 100 kilometers long. The Toba super-eruption was the biggest volcanic blast on Earth in the past 2.5 million years, and probably further back than that as well. There were also massive eruptions at Yellowstone 640,000, 1.3 million and 2.1 million years ago. Some theorize that the Toba eruption came close to wiping homo sapiens. They argue the human population shrunk to a few thousand after the event (See Below).
Researchers estimate some 2,000-3,000 cubic environmental of rock and ash were ejected from the volcano when it exploded. It was only in 1929 that a Dutch geologist recognized the lake as a caldera. A caldera is essentially a great hole that occurs in the Earth’s surface after a great amount of material has been removed by a massive volcanic eruption. The central part of Yellowstone National Park is caldera—measuring 35-by-45-mile (60-by-70-kilometer)—about the same size as Lake Toba. Eruptions that leave calderas are rare. The one at Toba seems occur every a 400,000 years or so. [Source: Joel Achenbach, National Geographic, March 2005]
Today, Lake Toba is about 80 kilometers (50 miles) long, 25 kilometers (16 miles) across and has a depth of 450 meters (1,400 feet) and covers 1,145 square kilometers (685 square miles). Fringed in most places by steep cliffs, the lake is a caldera left over from the blast that occurred 71,000 year ago, which deposited a layer of ash and pumice 2000 feet to the north of the lake. Lake Toba (Danai Toba) is the largest lake in Southeast Asia and, according to the Guinness Book of Records, the world's largest and deepest volcanic crater. The lake is so big an island almost the size of Singapore could fit inside it.
According to volcano.oregonstate.edu: “The caldera is 18 x 60 miles (30 by 100 kilometers) and has a total relief of 5,100 feet (1700 m). The caldera probably formed in stages. Large eruptions occurred 840,000, about 700,000, and 75,000 years ago. The eruption 75,000 years ago produced the Young Toba Tuff. The Young Toba Tuff was erupted from ring fractures that surround most or all of the present-day lake. Samosir Island and the Uluan Peninsula are parts of one or two resurgent domes. Lake sediments on Samosir indicate at least 1,350 feet (450 meters) of uplift. Pusukbukit, a small stratovolcano along the west margin of the caldera, formed after the eruption 75,000 years ago. There are active solfataras on the north side of the volcano. [Source: volcano.oregonstate.edu /^\]
“Comparison of volumes produced by some of the greatest volcanic eruptions. The Young Toba Tuff has an estimated volume of 2,800 cubic kilometers (km) and was erupted about 74,000 years ago. The Huckleberry Ridge Tuff, erupted at Yellowstone 2.2 million years ago, has a volume of 2,500 cubic kilometers. The Lava Creek Tuff, erupted at Yellowstone 600,000 years ago, has a volume of 1,000 cubic kilometers. The May 1980 eruption of Mount St. Helens produced 1 cubic kilometers of ash. Not shown is the Fish Canyon Tuff of the San Juan Mountains of Colorado. The Fish Canyon Tuff was erupted 27.8 million years ago and has an estimated volume of 3,000 cubic kilometers. /^\
“The volume of the youngest eruption is estimated at 2,800 cubic kilometers, making the eruption the largest in the Quaternary. Pyroclastic flows covered an area of at least 20,000 square kilometers. Up to 1200 feet (400 meters) of Young Toba Tuff is exposed in the walls of the caldera. On Samosir Island the tuff is more than 1800 feet (600 meters) thick. Ash fall from the eruption covers an area of at least 4 million square kilometers (about half the size on the continental United States). Ash from the eruption has been recovered from deep-sea cores taken in the Bay of Bengal and in India, roughly 300 miles (500 kilometers) inland (1,900 miles, 3100 kilometers from Toba). Rose and Chesner suggested the ash may have reached central Asia and the Middle East. Ninkovich and others (1978) estimated of the height of the eruption column to be 30 to 50 miles (50 to 80 kilometers) for the Young Toba Tuff. Rose and Chesner, after a study of the shapes of the ash shards, concluded this estimate was too high by a factor of 5 or more. The pumice erupted 75,000 years ago is calc-alkalic quartz-latite to rhyolite in composition (68 percent-76 percent silica). /^\
“There have been no eruptions at Toba in historical time. The area is seismically active with major earthquakes in 1892, 1916, 1920-1922, and 1987. Toba is located near the Sumatra Fracture Zone (SFZ). Stratovolcanoes in Sumatra are part of the Sunda arc. Volcanism is the result of the subduction of the Indian Ocean plate under the Eurasian plate. The subduction zone is marked by the Java Trench. The geologic symbol for a subduction zone is a line with "teeth" (black triangles). The teeth are on the over-riding plate (the Eurasian plate in this case). The rate of subduction is 6.7 cm per year. From Knight and others (1986).” /^\
Toba's Eruption Changed Life on Earth?
Joel Achenbach wrote in National Geographic, “Once upon a time a volcano killed almost everybody. It's a radical and scary thought, but there's reason to think it may be true. Toba appears to have ejected some 670 cubic miles (2,790 cubic kilometers) of material, as much as 560 times the amount produced by Mount Pinatubo in 1991. The ash and gas from Toba reached 30 miles (50 kilometers) into the stratosphere and shrouded the entire planet. A super-eruption has multiple effects on the biosphere. Sulfur dioxide combines with water vapor to form sulfuric acid particles that scatter, reflect, and absorb sunlight. The planet's surface cools, the stratosphere heats, photosynthesis is reduced. [Source: Joel Achenbach, National Geographic, March 2005 >>>]
“The more immediate effects are equally devastating. Bill Rose, a volcanologist at Michigan Tech University, is particularly interested in the fine ash produced by volcanoes. The ash rains from the sky in particles so small that they can penetrate an animal's lungs. "It's like smoking," he says. "The birds die first," says Rose. "They get the ash in their feathers and they're immobilized. Then the larger animals start to die." A lot of the humans died too, says Stanley H. Ambrose of the University of Illinois at Urbana-Champaign. Indeed, studies of mitochondrial DNA in humans point to a possible bottleneck of genetic diversity at roughly the same time as Toba's eruption, although it's impossible to prove a link. >>>
“Ambrose does believe, however, that human behavior shows signs of change after Toba. Prior to the eruption, there's little evidence that humans engaged in long-distance networking. Afterward, humans in Kenya, some 4,000 miles (6,400 kilometers) from Toba, appear to have traveled up to 200 miles (300 kilometers) carrying obsidian objects. Ambrose's theory is that humans who learned to cooperate and give gifts would survive another crisis better than those who lived in isolated groups and did not practice altruism or reciprocity.” >>>
Toba Catastrophe Theory
According to the Toba catastrophe theory, modern human evolution was affected by a recent, large volcanic event. According to the Toba catastrophe theory, a massive volcanic eruption changed the course of human history by severely reducing the human population. This may have occurred when around 70–75,000 years ago the Toba caldera in Indonesia underwent a category 8 or "mega-colossal" eruption on the Volcanic Explosivity Index. This may have reduced the average global temperature by 3 to 3.5 degrees Celsius for several years and may possibly have triggered an ice age. This massive environmental change is believed to have created population bottlenecks in the various species that existed at the time; this in turn accelerated differentiation of the isolated human populations, eventually leading to the extinction of all the other human species except for the branch that became modern humans. [Source: Wikipedia]
On a variation of the Toba catastrophe theory, Stephen Oppenheimer of the Bradshaw Foundation wrote: The mega-bang from Toba super-eruption “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. Toba ash is also found in the Greenland ice-record and submarine cores in the Indian Ocean, allowing a precise date marker. India bore the brunt of the massive ash fall, and may have suffered mass extinction, since the Toba plume spread north-west across the Indian Ocean from Sumatra. This event may explain why most Indian maternal genetic sub-groups of the two founder lines M & N are not shared elsewhere in Asia and the dates of their re-expansions are paradoxically younger in India than elsewhere in East Asia and Australasia. [Source: Stephen Oppenheimer, Bradshaw Foundation *^*]
“If our ancestors left Africa 85,000 years ago, their descendants would have lived in Asia over 10,000 years before the Toba explosion, and beachcombers around the Indian Ocean would have been in direct line for the greatest volcanic ash fall in the whole of human existence. The Toba eruption is thus a valuable date mark, since the ash covered such a wide area, is accurately dated, and can be identified wherever an undisturbed layer of it is found. The early archaeological dates for human presence in Australia have been reinforced by an extraordinary reappraisal of the Kota Tampan Palaeolithic culture found in Lenggong Valley, in Perak on the Malay Peninsula. Malaysian archaeologist Zuraina Majid has explored the remains of this human culture in a wooded valley in Perak State, near Penang. A continuous Palaeolithic tradition known as the Kota Tampan culture goes back tens of thousands of years there. At one site, tools from this tradition lie embedded in volcanic ash from Toba. If the association of the tools with modern humans is confirmed, this means that modern humans got to Southeast Asia before the Toba eruption – more than 74,000 years ago. This, in turn, makes the 85,000-year-old exodus more likely. Genetic and other evidence for a human occupation of Australia by 65,000 years ago fits this scenario. *^*
“How does such an early date for the exodus fit with the genetic data? This is perhaps the most controversial and exciting part of the story. The short answer is that the genetic dates and tree fit the early exodus well. This also resolves the question about the origins of the Europeans: why it was that Europe was colonized only after 50,000 years ago, yet arose from the same maternal ancestor as the Australians and Asians. The South Asian region, the first homeland of that single, successful southern exodus, shows the presence of the genetic roots of that expansion not only in the so-called aboriginal peoples around the Indian Ocean, but among the bulk of the modern populations. Among these roots we can detect genetic base camps for the most westerly of the subsequent pioneer treks inland to the vast Eurasian continent. These treks set off, after a pause, for Europe, the Caucasus, and Central Asia. It seems that the vanguard of the beachcombing trail retained a surprising proportion of the original genetic diversity left in the out-of-Africa group and moved rather faster round the shores of the Indian Ocean. So fast, in fact, that they travelled right round to Indonesia and on into Near Oceania, arriving in Australia long before their first cousins made it to Europe.” *^*
Toba Catastrophe Theory Dismissed
In April 2013, Jonathan Amos of BBC News wrote: “The idea that humans nearly became extinct 75,000 ago because of a super-volcano eruption is not supported by new data from Africa, scientists say. In the past, it has been proposed that the so-called Toba event plunged the world into a volcanic winter, killing animal and plant life and squeezing our species to a few thousand individuals. An Oxford University-led team examined ancient sediments in Lake Malawi for traces of this climate catastrophe. It could find none. "The eruption would certainly have triggered some short-term effects over perhaps a few seasons but it does not appear to have switched the climate into a new mode," said Dr Christine Lane from Oxford's School of Archaeology. "This puts a nail in the coffin of the disaster-catastrophe theory in my view; it's just too simplistic," she told BBC News. The results of her team's investigation are published in the Proceedings of the National Academy of Sciences (PNAS). [Source: Jonathan Amos, BBC News, April 30, 2013 |=|]
“Researchers estimate some 2,000-3,000 cubic kilometres of rock and ash were thrown from the volcano when it blew its top on what is now Sumatra. Much of that debris landed close by, piling hundreds of metres deep in places. But a lot of it would also have gone into the high atmosphere, blocking out sunlight and cooling the planet. Sulphurous gases emitted in the eruption would have compounded this effect. Some scientists have argued that the winter conditions this would have induced could have posed an immense challenge to early humans and have pointed to some genetic studies that indicated our ancestors likely experienced a dramatic drop in numbers - a population "bottleneck" - around the time of the eruption. |=|
“The Oxford team reasoned that if this perturbation was so great, it ought to be evident in the sediments of Lake Malawi. This body of water is some 7,000 kilometers west of Toba in the East African Rift Valley, from where our Homo sapiens species emerged in the past 100,000 years or so. The lake is said to retain an excellent record of past climate change which can be inferred from the types and abundance of algae and other organic matter found in its bed muds. Tens of metres of sediments have been drilled to retrieve cores, and it these recordings of past times that Dr Lane and colleagues examined. They identified tiny glass shards mixed in with the muds almost 30m below the lake bed. The shards represent small fragments of magma ejected from a volcano that have "frozen" in flight. "They're smaller than the diameter of a human hair, less than 100 microns in size," explains Dr Lane. "We find them by sieving the sediments in a very long process that goes through every centimetre of core." Chemical analysis ties the fragments to the Toba eruption. |=|
“The shards are present only in traces, but indicate the eruption spewed ash much further than previously thought - about twice the distance recorded in other studies. But the investigation finds no changes in the composition of the sediments that would indicate a significant dip in temperatures in East Africa concurrent with the Toba eruption. What is more, the presence of the shards has allowed researchers to more accurately time other climate events that are seen in the cores. This includes a group of huge droughts previously dated to occur some 75,000 years ago. These have now been pushed back at least 10,000 before the eruption. "All long records like the Malawi cores are very difficult to date, particularly when you get beyond the limits of radiocarbon dating which is 50,000 years. So having a time marker like Toba in the cores is really exciting."
Major reductions in population size leave their mark on genetic diversity of modern individuals. For Homo sapiens, such bottlenecks are evident some 100,000 years ago and 50,000-60,000 years ago - both probably related to migrations out of Africa. Dr Chris Tyler Smith studies genetics and human evolution at the Wellcome Trust Sanger Institute in Cambridge, UK. He said the Toba theory was a popular one a few years ago, but more recent study had led most researchers to move on from the subject. "It was an exciting idea when it was first suggested but it just hasn't really been borne out by subsequent advances," he told BBC News. Dr Lane's team included Ben Chorn and Thomas Johnson from the University of Minnesota, Duluth, US.
Text Sources: New York Times, Washington Post, Los Angeles Times, Times of London, Lonely Planet Guides, Library of Congress, Compton’s Encyclopedia, The Guardian, National Geographic, Smithsonian magazine, The New Yorker, Time, Newsweek, Reuters, AP, AFP, Wall Street Journal, The Atlantic Monthly, The Economist, Global Viewpoint (Christian Science Monitor), Foreign Policy, Wikipedia, BBC, CNN, and various books, websites and other publications.
© 2008 Jeffrey Hays
Last updated June 2015