"A
supervolcano is a
volcano capable of producing a
volcanic eruption with an
ejecta mass greater than 10^15 kg (10^12 t).
Supervolcanoes occur when
magma in the
mantle rises into the
crust but is unable to break through it and pressure builds in a large and growing magma pool until the crust is unable to contain the
pressure.
This can occur at
hotspots (for example,
Yellowstone Caldera) or at
subduction zones (for example,
Toba). Another setting for the eruption of very large amounts of volcanic material is in
large igneous provinces, which can cover huge areas with
lava and
volcanic ash, causing long-lasting
climate change (such as the triggering of a small
ice age or
global warming), which can
threaten species with extinction.
The Oruanui eruption of New Zealand's Taupo Volcano, the world's most recent supereruption, had a Volcanic Explosivity Index of 8."
Consequences
- volcanic dust in stratosphere - volcanic winter (land cooling of 5 - 15 C, ocean surface cooling 2 - 6 C)
- high atmospheric opacity, reduction of light levels
- drop in photosynthesis of plants due to reduced light and temperatures
- resistance of plants varies - the most sensitive are tropical forests
- problematic also for other types of forests when there is a temperature drop during the growing season
- decreased ocean productivity
- severe challenge to modern civilization (collapse of agriculture, followed by famine, the spread of infectious diseases, breakdown of infrastructure, social and political unrest, and conflict)
- Asian rice crop could be destroyed by a single night of below-freezing temperatures during the growing season
- in Canada, a 2-3°C average local temperature drop would destroy wheat production, and 3-4°C
would halt all Canadian grain production
- crops in the American Midwest and the Ukraine could be severely injured by a 3-4°C temperature decrease
- large volcanic eruptions might lead to longer term climatic change through positive feedback effects on climate such as cooling the surface oceans, formation of sea-ice, or increased land ice
- mitigation strategy could involve the stockpiling of global food reserves
At present, a global stockpile equivalent to a two-month global supply of grain exists, which is about 1 5 % of annual consumption. For a super-volcanic catastrophe, however, several years of growing season might be curtailed, and hence a much larger stockpile of grain and other foodstuffs would have to be maintained, along with the means for rapid global distribution.
