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>> A really huge volcanic eruption could change atmospheric chemisty and
>> therefore climate in a big way, but to be honest this seems to me
>> like a much less efficient way to cause massive extinctions in the
>> oceans than slamming a gigantic asteroid into a carbonate shelf.
>Not one huge volcanic eruption - nearly continuous, massive lava
>flows and lesser eruptions for several hundred thousand to a few
>This is *continuous* disruption of the atmosphere for many, many
>The sort of volcanism seen in the deposition of flood basalts
>is not found anywhere on Earth today, so we have no intuitive
>model of what it would have been like.
>The closest thing I know of is the Iceland Hot Spot, but that
>is not really the same at all.
There are two basic types of volcanism. One type is explosive that puts out
massive amounts of dust into the stratosphere, and little or no lava. Krakatoa
and St.Helens are examples of this type. They are rare as it takes millenia of
pressure buildup to produce the explosive events. The second type is a
continuous venting, often accompanied by lava flows. The Deccan Traps is an
example of this type. This kind of event releases gas into the lower atmosphere
but no dust into the stratosphere, and thus I doubt that it could produce the
kind of "nuclear winter" and extinction that an impact could. It could, however,
contribute to greenhouse warming.