Volcanoes have been erupting for billions of years, but humans have been around to record them with varying degrees of accuracy for only tens of thousands of years, and with precise, scientific rigor only since the early 20th century. Still, even though many of the planet’s most catastrophic eruptions occurred long ago, modern-day scientists have developed means for rating them.
Scientists with the U.S. Geological Survey use the Volcano Explosivity Index (VEI) to measure the magnitude of volcanic blasts. It’s a logarithmic scale that runs from 1 to 8. A magnitude 1 eruption spews less than 350,000 cubic feet (10,000 cubic meters) of volcanic tephra, which consists of ash and rocks; a magnitude 8 eruption puts out more than 240 cubic miles (1,000 cubic kilometers) of the stuff.
In recent history, the 1815 eruption of Mount Tambora Indonesie has been the most violent volcanic eruption and also the most deadly, killing 92,000 people. Video Tambora
The biggest one we have direct written records of would be Santorini, about 200 km (120 mi) southeast from Greece’s mainland,around 1630 BCE. However, the Taupo eruption of New Zealand in the year 186 was larger—only no one lived there at the time.
But the really huge ones were long before those. The largest since the rise of modern humans, Homo sapiens, is the great eruption of Toba, in Sumatra, Indonesie about 71,000 years ago. It produced some 2800 cubic kilometers of ash and may have reduced the world’s human population to only 10,000 people (Read below: Extract from “Journal of Human Evolution”) and the Huckleberry Ridge Tuff Eruption of Yellowstone Caldera, USA, which occurred approximately 2.1 million years ago.
The largest eruption we have firm evidence for in geologic history is the La Garita Caldera eruption in Colorado about 28 million years ago, in the Oligocene Epoch. That put 5000 cubic kilometers of lava into play. There might be larger ones, but the farther back in time we go, the more geologic evidence is destroyed by tectonic activity. list of the largest calderas on Earth
Finally, it is likely that the most powerful eruptions ever were the Siberian Traps in the Russian region of Siberia, about 250 million years ago. The highest ranking on the volcanic scale is VEI 8; These are super eruptions. Yellow Stone and Lake Toba caldera were both VEI8′s and Tambora was a VEI 7. But the Siberian traps would have been far off the scale. The Siberian traps were likely responsible for a mass extinction: the death of 95% of all life on Earth.
The world around 260 million years ago, not long before the eruptions forming the Siberian Traps occurred on the eastern shore of the shallow sea (paler blue) at the north of the map.
Extract from “Journal of Human Evolution”
by Professor Stanley H. Ambrose,
Department of Anthropology, University Of Illinois, Urbana, USA
Extract from “Journal of Human Evolution”  34, 623-651
The last glacial period was preceded by 1000 years of the coldest temperatures of the Late Pleistocene, apparently caused by the eruption of the Mount Toba volcano. The six year long volcanic winter and 1000-year-long instant Ice Age that followed Mount Toba’s eruption may have decimated Modern Man’s entire population. Genetic evidence suggests that Human population size fell to about 10,000 adults between 50 and 100 thousand years ago. The survivors from this global catastrophy would have found refuge in isolated tropical pockets, mainly in Equatorial Africa. Populations living in Europe and northern China would have been completely eliminated by the reduction of the summer temperatures by as much as 12 degrees centigrade.
Volcanic winter and instant Ice Age may help resolve the central but unstated paradox of the recent African origin of Humankind: if we are all so recently “Out of Africa”, why do we not all look more African?
Because the volcanic winter and instant Ice Age would have reduced populations levels low enough for founder effects, genetic drift and local adaptations to produce rapid changes in the surviving populations, causing the peoples of the world to look so different today. In other words, Toba may have caused Modern Races to differentiate abruptly only 70,000 years ago, rather than gradually over one million years.
The Mount Toba eruption is dated to approximately 71,000 years ago. Volcanic ash from Mount Toba can be traced north-west across India, where a widespread terrestrial marker bed exists of primary and reworked airfall ash, in beds that are commonly 1 to 3, and occasionally 6 meters [18 feet] thick.
Tambora, the largest known historic eruption, displaced 20 cubic kilometres of ash. Mount Toba produced 800 cubic kilometres.* It was therefore forty times larger than the largest eruption of the last two centuries and apparently the second largest known explosive eruption over the last 450 million years.
VOLCANIC WINTER AND DIFFERENTIATION OF MODERN HUMANS
Mount Toba’s eruption is marked by a 6 year period during which the largest amount of volcanic sulphur was deposited in the past 110,000 years. This dramatic event was followed by 1000 years of the lowest ice core oxygen isotope ratios of the last glacial period. In other words, for 1000 years immediately following theeruption, the earth witnessed temperatures colder than during the Last Glacial Maximum at 18-21,000 years ago.
For the volcanic aerosols to be effectively distributed around the earth, the plume from the volcanic eruptions must reach the stratosphere, a height greater than 17 kilometres. Mount Toba’s plume probably reached twice this height. Most solar energy falls at low latitudes between the Tropics of Cancer and Capricorn, so eruptions that happen near the Equator cause much more substantial cooling due to the reflection of solar energy. Toba lies 2 degrees north of the Equator, on the Island Sumatra.
The reduction in atmospheric visibility due to volcanic ash and dust particles is relatively short-lived, about three to six months. Longer-term global climatic cooling is caused by the highly reflective sulphuric acid haze, which stays suspended in the upper atmosphere for several years.
Ice core evidence implicates Mount Toba as the cause of coldest millennium of the late Pleistocene. It shows that this eruption injected more sulphur that remained in the atmosphere fo a longer time [six years] than any other volcanic eruption in the last 110,000 years. This may have caused nearly complete deforestation of southeast Asia, and at the same time to have lowered sea surface temperatures by 3 to 3.5 degrees centigrade for several years.
If Tambora caused the ” The year without a summer” in 1816, Mount Toba could have been responsible for six years of relentless volcanic winter, thus causing a massive deforestation, a disastrous famine for all living creatures, and a near extinction of Humankind.
The Volcanic Winter/Weak Garden of Eden model proposed in this paper. Population subdivision due to dispersal within African and other continents during the early Late Pleistocene is followed by bottlenecks caused by volcanic winter, resulting from the eruption of Toba, 71 ka. The bottleneck may have lasted either 1000 years, during the hyper-cold stadial period between Dansgaard-Oeschlger events 19 and 20, or 10ka, during oxygen isotope stage 4. Population bottlenecks and releases are both sychronous. More individuals survived in Africa because tropical refugia were largest there, resulting in greater genetic diversity in Africa.
BLOMBOS CAVE: 77,000 YEARS OLD
Small and portable, this red ochre stone is engraved with what must be “tally” marks. It is one of two such stones recently found in the Blombos Cave in South Africa and have been dated as being 77,000 years old, making them the oldest form of recorded counting ever found.
The stone is worn which probably indicated that it was constantly handled over a period of time, how long is impossible to tell. It looks as though the stone has been reused at least once before as the lighter marks appear to have been erased rather than worn away naturally.
If the dating is accurate this stone was used 5000 years before the Mount Toba eruption of 71,000 years ago. The evidence from the Toba eruption indicates that the world’s population of Modern Manwas reduced to a total of around 10,000 adults.