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 Toba St. Helens
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: • 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-BB43-146C- BB4383414B7F0000> (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