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

2. 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)

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

4. 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

5. 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

6. 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

7. 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

8. 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.

9. 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.

10. 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.

11. Lake Toba
60 miles long
18 miles wide

12. 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
-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.

13. (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.

14. 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.

15. 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.

16. (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.

17. 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

18. 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?