The Eruption of the Toba Supervolcano ca. 72,000 B.C. and Its Effects on the Early Human Population

72,000 B.C. Humankind may have been nearly wiped out forever by the volcano under what would become Lake Toba; a massive flooded volcanic crater (caldera) today. It was by far the largest volcanic eruption ever witnessed in the history of man. (woman man)

Discovery of Volcano 1929: Ignimbrite (rock deposited by pyroclastic flows) discovered around sides of lake by Dutch geologist Rein van Bemmelen.

van Bemmelen reasoned that Lake Toba was a gigantic Evidence for massive Plinian, rhyolitic (explosive) volcanic activity around/involving Lake Toba sometime in the distant past. van Bemmelen reasoned that Lake Toba was a gigantic caldera (mountaintop collapsed by volcanism). A more familiar example of a volcanic caldera: Crater Lake, Oregon

Evidence Elsewhere -Layer of ash identified with Toba eruption found all over Asia and worldwide -Called “Young Toba Tuff” -Up to 20 feet deep in certain locations on Indian subcontinent

How big was it? A modern comparison Mt. St. Helens (WA), 1980: most well-known example of Plinian-style eruption. -Highly explosive -Large ash cloud -Pyroclastic flows

A fairly substantial eruption. Mount St. Helens: A fairly substantial eruption. Eruption deposits/ pyroclastic flows devastated 230 square miles of forest Ash fell over 12 U.S. states; carried halfway across the continent

The Toba eruption was thus And that’s basically what happened. Mount St. Helens: 0.26 cubic miles ejected. Toba Supervolcano: 670 cubic miles ejected (estimate). The Toba eruption was thus (670)/(0.26) = 2,577 times as big as Mount St. Helens.

So basically, picture this going on for nine hours, which was the Mount St. Helens eruption… and then picture 2,576 other volcanoes just like it erupting alongside for that duration. That’s how much ash Mount Toba produced.

We’ve seen what kind of eruption could produce a crater like this. Crater of Mount St. Helens 1.2 miles wide 1.8 miles long We’ve seen what kind of eruption could produce a crater like this.

Lake Toba 60 miles long 18 miles wide

So, huge eruption. So what? -Keep in mind: Eruption of Mount Tambora in 1815 blocked out enough sunlight for a year to cause worldwide “Year Without a Summer.” -70-90,000 perished from starvation in 1815-16 -Crops failed worldwide Yet Tambora was only a VEI 7 and only erupted ~38.6 cubic miles of tephra. Toba is estimated to have erupted 670 cubic miles.

(Probable) Climatic Effects of Toba Ice core samples from Antarctica and Greenland: 6-year period of sulphur deposition far above normal levels – sulphur and volcanic ash remained in atmosphere, blocking out substantial amounts of sunlight. – Nuclear Winter for 6—10 years. Global circulation of ash from Mount Pinatubo, 1991 – atmospheric presence of Toba Tuff was undoubtedly far more extensive.

Toba was also situated at the worst location possible for a supervolcano. Proximity to equator ~ ability to affect all latitudes of globe, and for tephra circulation to be affected by trade winds. Here is Toba, at 2 degrees north of the equator.

Greenland: Temperature dropped Resulting Scenario -Past temperatures on Earth can be determined by measuring the ratio of Oxygen-16 atoms to Oxygen-18 within ice cores. -Conducting this process with ice cores taken from Greenland and Antarctica: Toba event  coldest 1,000 years in last glacial period (last ~110,000 years), possibly with exception of last ice age. Greenland: Temperature dropped 16* C in 160 years.

(controversial theory) Effect on Humankind (controversial theory) -Homo sapiens is remarkable for lack of genetic diversity in comparison to other primates. -Two possible explanations: Evolution slowed by ability to artificially protect oneself – but too recent? 2) Normal evolution; resulting diversity cut off by recent genetic “bottleneck.” “Bottleneck” scenario: Colossal near-species-extinction level event leaves small # of individuals remaining, who become the genetic root of the species.

How it might have happened Mount Toba eruption: -Recent (only 74,000 years) -Global temperature drop of 5-15* C -Up to 20 feet of ash deposited in places No more convincing suspect for “bottleneck” scenario. Most well-known proponent of this theory: Stanley H. Ambrose, University of Illinois at Urbana. How it might have happened

If this theory is correct: -Eruption of Mount Toba 74,000 years ago may have nearly killed off humankind. -Volcanic winter lasted six years, according to sulfur deposits; at the end of those six years only a few thousand or ten thousand humans might have remained. -Will a geological catastrophe ever push humankind to the brink again? Stone found in Blombos Cave, South Africa, dating from 77,000 years ago (3,000 years before Toba). Did any of the carver’s descendants survive?