Doomsday: She's Gonna Blow

Earth is humanity’s cradle, but by no means can it completely harbour us from harm. Many risks threaten individual lives, but there are some catastrophic enough to wipe out entire species. Is it possible for the prolific human species to face extinction?

Volcanoes cause much disruption in their own right. However, much larger supervolcanoes do exist, with as many as eleven likely hotspots found around the world. Should one erupt, the surrounding area will certainly be levelled and buried, and the broader world would go through an unseasonal winter.

History
There are countless examples of volcanic eruptions throughout human history, let alone throughout the life of planet Earth. A more famous one occurred in AD 79 when Mt. Vesuvius erupted. Nearby Pompeii and Herculaneum were buried under several metres of pumice, sudden enough to preserve the inhabitants in their original positions.

A larger one occurred in 1815 when Tambora erupted. It released enough material to convert the northern summer into a winter. Famine prevailed when summer crops failed.

A supervolcano eruption occurred 640 000 years ago from the ground under Yellowstone National Park. As human society was nary advanced during that time, there was limited impact to humanity. This eruption occurs (on average) every 600 000 years, so the next one is statistically overdue. The Lake Toba super eruption as recent as 70 000 years ago was severe enough reduce the human population to a few thousand. This qualified Homo sapiens as an endangered species in the aftermath.

Radiation hazard

The Earth's core is radioactive. Despite the Earth's age, there is still radioactive material beneath the surface that needs to decay. When it does, it releases energy, of which includes heat. The amount of heat that is trapped inside the Earth is enough to turn the rock molten, giving rise to processes like plate tectonics.

Of course, once this heat is liberated from the rock, it still needs somewhere to go, and this always means out. Enough pressure builds up over time to allow the heat (along with some rock material) to burst forth through the cooler, solid crust. When this happens, a volcanic eruption occurs.

The molten magma feeding a volcano always forms a chamber where it rests until it is time. That of a supervolcano is many kilometres wider, allowing for potentially many cubic kilometres of material to be ejected.

A satellite photo of the Lake Toba caldera.

Brrrrrrrrrrrrrr
A supervolcano, just like any volcano, will release two types of material into the atmosphere in an eruption:

• Volcanic ash
• Sulphur dioxide, which will dissolve in water vapour to form sulphuric acid:

2SO₂ + 2H₂O + O₂ → 2H₂SO₄

This material will block out the Sun's radiance, preventing life below from basking in its glory. Sulphuric acid is shiny enough (hence its old name 'oil of vitriol') to reflect the light back to space. The resulting cooling will give rise to a nuclear winter. Volcanic ash is very fine while sulphuric acid is a liquid, so they will persist in the atmosphere for years.

Consequences of a super eruption

• Complete levelling of surrounding area and burial in volcanic ash
• Mass extinctions
• Crop failure
• Famines

Conclusions

• 2012-compatible? Yes
• Will the world end with a bang or whimper? Whimper (overall)
• Armageddon or Ragnarok? Armageddon in the surrounding area, Ragnarok in the rest of the world

Bibliography

• Dean, Tim (2008), 'Doomsday', Cosmos, no. 22.
• Naked Science: Big Freeze (2006), television program, National Geographic Channel.
• Naked Science: Preventing Armageddon (2010), television program, National Geographic Channel.
• Naked Science: Vesuvius Time Bomb (2009), television program, National Geographic Channel.
• Plate tectonics, wiki article, Wikipedia, viewed 29 April 2011, <http://en.wikipedia.org/wiki/Plate_tectonics>.

EDIT 20May11: Appended chemical equation for hydration/oxidation of sulphur dioxide.

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