Aslkahuna wrote:Actually, it's not so much the dust and ash that causes the problem but the Sulphur Dioxide a volcano blows into the atmosphere (34 million metric tons worth in the case of Pinatubo. The SO2 forms Sulfuric acid aerosols which does the dirty work in the atmosphere including doing a major number on the O3 layer. The dust falls out fairly rapidly-in fact, in October 1991 we were getting dust fallout from Pinatubo here in AZ. I was stuck by the obvious dimming of sunlight as well and had a pyranometer graph made up of an early October day pre Pinatubo and one in 1991. The early graph had the typical Bell curve while the 1991 one had a flat top during the three hour period around Local Noon and everywhere the curve was below the early curve. The Sulfuric acid haze also affected nighttime observation of the sky for a number of years afterwards.
Steve
It's really hard to say how much SO2 was released in some of these larger eruptions. Especially El Chichon's in 1982. I have read before that El Chichon released both eight million tons and twenty million tons. I also even read claims about it releasing more than Pinatubo even though the latter sent more ash etc...
The El Chichon eruption also shed light on something that we were unaware of. We did not even realize that we could observe the SO2 in the stratosphere until the TOMS satellite started measuring extreme ozone levels over Mexico right after the eruption. They soon figured out it was the SO2 absorbing the UV light and not higher ozone levels.
This goes to show how young our knowledge of the stratosphere is and there are still many other things we have yet to understand.
Jim