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?
Volcanic
Winter
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.
*Mount St Helens produced a tiny 0.2 cubic kilometres.
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.
*Mount St Helens produced a tiny 0.2 cubic kilometres.
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 the eruption, 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 for 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.
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 for 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.
Source:
Professor Stanley H. Ambrose
Department of Anthropology, University Of Illinois, Urbana
Professor Stanley H. Ambrose
Department of Anthropology, University Of Illinois, Urbana