The Long Winter

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2006 A.D.
Chris Rollins
Lake Toba (Danau Toba), Sumatra, Indonesia
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A minor tourist destination today, the lake seems
peaceful enough.
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Little would seem to suggest that its origins are
different from those of any other lake..
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72,000 B.C.
Humankind may have been nearly wiped out forever
by the volcano under what would become Lake
Toba, actually a massive flooded volcanic crater
(caldera) today. It was by far the largest
volcanic eruption ever witnessed in the history
of man. (woman man)
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The Eruption of the Toba Supervolcano ca. 72,000
B.C. and Its Effects on Population
Chris Rollins GEOL 108 Dr. A Fall 2006 Powerpoint
Presentation
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Discovery of Volcano
1929 Ignimbrite (rock deposited by pyroclastic
flows) discovered around sides of lake by Dutch
geologist Rein van Bemmelen.
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• 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
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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
Closeup of Young Toba Tuff
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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
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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
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Volcanic Explosivity Index
Toba
St. Helens
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This doesnt mean that Toba was 8/5 (1.6) times
as big as St. Helens.
Like the Richter scale, each degree of VEI scale
10x bigger eruption, with regards to ejected
ash.
VEI Rating
Tephra (ash) ejected (cubic meters)
VEI 8 on the order of 1000x larger eruption
than VEI 5, in theory.
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And thats 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.
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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. Thats
how much ash Mount Toba produced.
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Crater of Mount St. Helens
1.2 miles wide 1.8 miles long
Weve seen what kind of eruption could produce a
crater like this.
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Lake Toba (Danau Toba)
60 miles long 18 miles wide
Holy silly?
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Heres an attempt at a rendering of a
supervolcano eruption by the Discovery Channel.
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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.
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(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.

Global circulation of ash from Mount Pinatubo,
1991 atmospheric presence of Toba Tuff was
undoubtedly far more extensive.
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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.
(Arctic supervolcano would probably have little
effect on S. hemisphere)
Here is Toba, at 2 degrees north of the equator.
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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.
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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.
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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
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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 carvers descendants
survive?
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Sources
Ambrose, Stanley H. Volcanic Winter, and
Differentiation of Modern Humans.
lthttp//www.bradshawfoundation.com/evolution/gt
(16 Nov 2006). Bindeman, Ilya N. The Secrets of
Supervolcanoes. Scientific American June 2006
lthttp//www.sciam.com/article.cfm?chanIDsa006c
olID1articleID0006E0BF-BB43-146C-
BB4383414B7F0000gt (16 Nov 2006). "Lake Toba."
Wikipedia, The Free Encyclopedia. 14 Nov 2006,
0800 UTC. Wikimedia Foundation, Inc.
lthttp//en.wikipedia.org/w/index.php?titleLake_To
baoldid87720193gt (16 Nov 2006). "Mount
Tambora." Wikipedia, The Free Encyclopedia. 17
Nov 2006, 1909 UTC. Wikimedia Foundation, Inc.
lthttp//en.wikipedia.org/w/index.php?titleMou
nt_Tamboraoldid88472009gt (16 Nov 2006).
Mystery of the Megavolcano. PBS, 2006
lthttp//www.pbs.org/wgbh/nova/megavolcano/gt (16
Nov 2006). Supervolcanoes. (Transcript of BBC
TV program aired February 3, 2000)
lthttp//www.bbc.co.uk/science/horizon/1999/supervo
lcanoes_script.shtmlgt (16 Nov 2006). Tilling,
Robert I, Lyn Topinka, and Donald A.
Swanson.Eruptions of Mount St. Helens Past,
Present and Future. U.S. Geological
Survey, 1990 lthttp//vulcan.wr.usgs.gov/Volca
noes/MSH/Publications/MSHPPF/MSH_past_present_futu
re.htmlgt (16 Nov 2006). Topinka, Lyn. Mount
St. Helens, Washington May 18, 1980 Eruption
Summary. U.S. Geological Survey, 1997
lthttp//vulcan.wr.usgs.gov/Volcanoes/MSH/May18/sum
mary_may18_eruption.htmlgt (16 Nov
2006). Weber, George. Toba Volcano.
lthttp//www.andaman.org/BOOK/originals/Weber-Toba/
textr.htmgt (16 Nov 2006).
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Other Images (not from those sources)
http//www2.ac-lyon.fr/enseigne/biologie/photossql
/images/danau_toba.jpg http//en.wikipedia.org/wik
i/ImageLake-toba.jpg http//www.nd.edu/mdemenez/
World/Indonesia/Indonesia-Images/20.jpg http//www
.rebas.demon.nl/weblog/uploaded_images/Sunset_Libe
rta_cur-3728-751029.jpg http//www.nationalgeograp
hic.com/forcesofnature/img/gallery/18_b.jpg http/
/www.dustydavis.com/blogimages/crater_lake_large.j
pg http//www.geology.sdsu.edu/how_volcanoes_work/
Images/Rock20Textures/ashflow_26s.jpg http//www.
rap.ucar.edu/general/asap-2005/Thur-AM2/Williams_D
oD_Satellites_files/slide0072_image034.jpg http//
zyx.org/Fig641.gif http//content.answers.com/main
/content/wp/en/b/b1/Toba_zoom.jpg http//www.exitm
undi.nl/supervolcano.gif http//www.pbs.org/wgbh/n
ova/volcanocity/images/dead-indonesia-l.jpg http/
/www.geo.arizona.edu/palynology/geos462/dustvolc.g
if http//earthquake.usgs.gov/eqcenter/recenteqsww
/Maps/10/100_0.gif http//www.zfl.uni-bonn.de/imag
es/small_kgi/IceCap_01.jpg