Transcript The Long Winter

2006 A.D.
Chris Rollins
Lake Toba (Danau Toba),
Sumatra, Indonesia
A minor tourist destination today,
the lake seems peaceful enough.
Little would seem to suggest that its origins are
different from those of any other lake..
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)
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
Discovery of Volcano
1929: Ignimbrite (rock deposited by pyroclastic flows) discovered
around sides of lake by Dutch geologist Rein van Bemmelen.
 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
Closeup of Young Toba Tuff
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
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
Volcanic Explosivity Index
St. Helens
Toba
This doesn’t 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.
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.
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
(Danau Toba)
60 miles long
18 miles wide
Holy silly?
Here’s an attempt at a rendering
of a supervolcano eruption
by the Discovery Channel.
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.
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.
(Arctic supervolcano would probably
have little effect on S. hemisphere)
Here is Toba,
at 2 degrees north
of the equator.
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.
Effect on Humankind
(controversial theory)
-Homo sapiens is remarkable for
lack of genetic diversity in
comparison to other primates.
-Two possible explanations:
1) 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.
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?
Sources
Ambrose, Stanley H. “Volcanic Winter, and Differentiation of Modern Humans.”
<http://www.bradshawfoundation.com/evolution/> (16 Nov 2006).
Bindeman, Ilya N. “The Secrets of Supervolcanoes.” Scientific American June 2006
<http://www.sciam.com/article.cfm?chanID=sa006&colID=1&articleID=0006E0BF-BB43-146CBB4383414B7F0000> (16 Nov 2006).
"Lake Toba." Wikipedia, The Free Encyclopedia. 14 Nov 2006, 08:00 UTC. Wikimedia Foundation, Inc.
<http://en.wikipedia.org/w/index.php?title=Lake_Toba&oldid=87720193> (16 Nov 2006).
"Mount Tambora." Wikipedia, The Free Encyclopedia. 17 Nov 2006, 19:09 UTC. Wikimedia Foundation, Inc.
<http://en.wikipedia.org/w/index.php?title=Mount_Tambora&oldid=88472009> (16 Nov 2006).
“Mystery of the Megavolcano.” PBS, 2006 <http://www.pbs.org/wgbh/nova/megavolcano/> (16 Nov 2006).
“Supervolcanoes.” (Transcript of BBC TV program aired February 3, 2000)
<http://www.bbc.co.uk/science/horizon/1999/supervolcanoes_script.shtml> (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
<http://vulcan.wr.usgs.gov/Volcanoes/MSH/Publications/MSHPPF/MSH_past_present_future.html>
(16 Nov 2006).
Topinka, Lyn. “Mount St. Helens, Washington: May 18, 1980 Eruption Summary.” U.S. Geological Survey,
1997 <http://vulcan.wr.usgs.gov/Volcanoes/MSH/May18/summary_may18_eruption.html>
(16 Nov 2006).
Weber, George. “Toba Volcano.” <http://www.andaman.org/BOOK/originals/Weber-Toba/textr.htm>
(16 Nov 2006).
Other Images (not from those sources)
http://www2.ac-lyon.fr/enseigne/biologie/photossql/images/danau_toba.jpg
http://en.wikipedia.org/wiki/Image:Lake-toba.jpg
http://www.nd.edu/~mdemenez/World/Indonesia/Indonesia-Images/20.jpg
http://www.rebas.demon.nl/weblog/uploaded_images/Sunset_Liberta_cur-3728-751029.jpg
http://www.nationalgeographic.com/forcesofnature/img/gallery/18_b.jpg
http://www.dustydavis.com/blogimages/crater_lake_large.jpg
http://www.geology.sdsu.edu/how_volcanoes_work/Images/Rock%20Textures/ashflow_26s.jpg
http://www.rap.ucar.edu/general/asap-2005/Thur-AM2/Williams_DoD_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.exitmundi.nl/supervolcano.gif
http://www.pbs.org/wgbh/nova/volcanocity/images/dead-indonesia-l.jpg
http://www.geo.arizona.edu/palynology/geos462/dustvolc.gif
http://earthquake.usgs.gov/eqcenter/recenteqsww/Maps/10/100_0.gif
http://www.zfl.uni-bonn.de/images/small_kgi/IceCap_01.jpg