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Why do volcanic clouds of ash cause lightening (like on Mt Pinatubo)?
Answer 1:

lightning is dependent on the existence of ways to produce a separation of charges on a large scale...lightning is the coming together of regions of positive and negative charge... this develops when you take a piece of rubber and rub wool against it...or take a glass rod and rub a silk cloth on it...this develops negative or positive charge...

same thing happens in a volcanic cloud....the tiny particles become charged and the turbulent winds bring a cloud of positive charges against a cloud of negative charges and ...WHAM, lightning !!!

you can read more about this in some books on volcanos...look up volcanic lightning.

Answer 2:

When a volcano erupts it discharges billions and billions of tiny particulates into the atmosphere about it.Some of those particulates can interact with the already existing atmosphere above the volcano and produce massive thunderstorms in a very short period of time. Lightening is sometimes so severe above a volcano eruption because a combination of the intense heat plus billions of particulates can result in a very dry, static atmosphere above the eruption, which sometimes produces severe lightening.



Answer 3:

Because volcanic clouds are tiny bits of dust, they can rub together as they blow by each other in the cloud. This acts just like rubbing your feet on the carpet and touching the doorknob on the other side of the room. You build up static electricity. The same thing happens inside of the cloud but on a much larger scale so instead of a tiny spark, you get giant sparks--lightning.



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