Super Volcanoes: Our Biggest Threat?

There are few natural disasters that pose a severe threat to our global civilization.  Tens of thousands of years ago, when our species lived exclusively in East Africa in small bands of 250-500 individuals, an earthquake, volcano, tsunami or hurricane could have pushed us to the brink of extinction.  However, there is still one natural disaster that we should be wary of: a super volcano.  Super volcanoes are rare events; there are only 10 known eruptions in the past 25 million years.  Despite this, when they do occur, they radically alter the biosphere and destabilize global temperature and climate for decades, sometimes centuries.

What Are Super Volcanoes?

Super volcanoes were classified in the 1980s by using a Volcanic Explosivity Index (VEI)(OurAmazingPlanet, 2011).  The VEI is a scale from one to eight that quantifies volcanic power, with each succeeding VEI being 10x greater than the last.  VEI 8 volcanic eruptions are classified as super volcanoes capable of reaching an ejecta volume of greater than 1000 km3.  Super volcanoes are thousands of times larger than normal volcanic eruption events (VEI 1).  Over the last 100,000 years our planet has experienced two VEI 8 eruptions.  One occurred 26,500 years ago in New Zealand and one occurred 74,000 years ago in what is today Lake Toba in Indonesia (Ninkovich, 1978).

Considerably more is known about the Lake Toba event, and all evidence indicates that it devastated the Austronesian and South Asian region (Owen, 2012).  The eruption itself may have lasted for more than two weeks producing pyroclastic flows (superheated gas and rock) that destroyed an area of 200,000 km2 and depositing over 600m of ash surrounding the site.  The effects of the blast were global, decreasing average temperature by 3-3.5 degrees Celsius for at least a decade and covering most of South Asia in 15cm of ash.

Around this time a few bands of our species had migrated out of East Africa into the Arabian Peninsula and areas of modern day India.  Mitochondrial DNA (mtDNA) evidence suggests that the super volcanic event seriously challenged our existence, slowed our expansion across Asia and led to a genetic bottleneck (Achenbach, 2005).  In between 50,000-100,000 years ago the human population fluctuated around 10,000 individuals (Impey, 2007).  If the genetic bottleneck was as severe as the mtDNA suggests, our population could have dwindled well below this average.  Many paleoanthropologists believe that in order to survive the global catastrophe, our species needed to fundamentally change our behaviour.  There is some evidence to suggest that post-eruption humans began ranging over longer distances in order to build more complex and stable trade networks that could withstand the destabilizing effects of such an event.

Will It Happen Again?

Volcanologists admit that it is exceptionally difficult to predict when a volcano will erupt, regardless of its potential size.  However, it is known that certain areas of the planet are hot spots for super volcanic activity in the past.  For example, Lake Toba, the site of the super volcanic eruption 74,000 years ago,seems to be on a 400,000 year cycle (Achenbach, 2005).  However, the super volcano underneath Yellowstone National Park may pose the most eminent threat to our species.  Although the Yellowstone supervolcano seems to be on a much longer cycle of approximately 2.0 million years, the last eruption occurred 2.1 million years ago producing one of the largest known eruptions in natural history.  If it were to erupt on a comparable scale to the eruptions 2.1, 4.5 and 6.0 million years ago the entire United States would need to be evacuated.  Most of the North America would be covered in a minimum of 1 cm of volcanic ash, and half of the United States would be covered in over 1 m of volcanic ash (Choi, 2012).  At least 2,500 km3 would be completely destroyed.  The ensuing volcanic winter would likely last for decades on a global scale and pose a significant threat to our civilization.  Although it is unlikely that it would cause complete extinction, it would probably take centuries to recover.

Luckily, most volcanologists agree that we shouldn’t expect the Yellowstone super volcano to erupt in our lifetime.  However, it is also probable that it will erupt soon on a geologic scale.  The restless caldera of red-hot molten lava is a hidden dragon underneath one of the world’s largest natural tourist attractions.  It may be impossible to predict exactly when the magma in the mantle will rise to the crust and break through, but it’s inevitable that it will happen one day.

References:

Achenbach, J.  2005.  Big Chill: How Toba’s eruption changed life on Earth.  National Geographic.  Accessed November 18 2012. http://ngm.nationalgeographic.com/ngm/0503/resources_who.html

Choi, C.Q.  2012.  Yellowstone’s supervolcano: Where is lava likely to erupt?  MSNBC: Technology and Science.  Accessed November 18 2012. http://www.msnbc.msn.com/id/49037141/ns/technology_and_science/t/yellowstones-supervolcano-where-lava-likely-erupt/#.UKlBqJhijdk

Impey, C.  2007.  The Living Cosmos.  New York: Random House.

Ninkovich, D. et al.  1978.  The exceptional magnitude and intensity of the Toba eruption, Sumatra: An example of the use fo deep-sea tephra layers as a geological tool.  Bulletin of Volcanology, 41, 286-298.

OurAmazingPlanet Staff.  2011.  10 Biggest Volcanic Eruptions in History.  Accessed November 18 2012. http://www.ouramazingplanet.com/1436-volcanoes-biggest-history.html

Owen, J.  2012.  Supervolcano Rained Aced on Both Poles – But Wasn’t So Bad After All?  National Geographic.  Accessed November 18 2012. http://news.nationalgeographic.com/news/2012/11/121107-toba-supervolcano-antarctica-ice-eruption-science/

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About Cadell Last
I am a science educator, freelance science writer, and founder of The Advanced Apes based in Toronto, Ontario. In the past my academic research focused on the evolution, ecology, and behaviour of non-human primates (i.e., chimpanzees, gorillas, ring-tailed lemurs). Currently, my official blog, The Ratchet, can be found via The Advanced Apes and Svbtle. I enjoy exploring recent research in human evolutionary sciences, as well as biology, ecology, astronomy, physics, and computer science. My work has been featured in Scientific American, American Humanist, Richard Dawkins Foundation for Reason and Science, and Jane Goodall Institute of Canada. I am also exploring science popularization in new mediums in collaboration with PBS Digital Studios with an animated YouTube channel. You can contact me on Twitter (@cadelllast) or via email: cadell.last@gmail.com

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