The only major effect volcanoes have on the ozone layer is because of the generation of sulfate aerosols. These are relatively short-lived, so the effect is not as permanent as with carbon-halogen covalently bonded compounds. The eruption of Mt Pinatubo (sp?) caused a decrease of ozone layer thickness of about 2-4%, depending on location, but this was resorbed at ~70%/year. I have no figures for the Mt St Helens 1980 eruption, would it was less important (geologically speaking). The physical effect of the emissions will be largely stopped at the tropopause, in the same manner as cumulonimbus thunder clouds forming their famous anvil-shaped head, but it is probable that the level of the tropopause would be pushed upwards 1,000 m or so, forming a "bubble". Transtropopausal transport mechanisms are very slow, so relatively little of the emissions gases or particles will reach the stratosphere before thet are rained out or destroyed by photolysis or hydrolysis (fortunately, otherwise there could be no ozone layer!). OTOH, there are transient increases of various greenhouse gases but their short-term effect is largely compensated by the transient increase of dust particles, causing cooling. In addition, the earth's albedo is locally increased during the time of the eruption by reflection of radiation from the clouds. All these points average out, over a few years, to an almost non-measurable effect on climate change, although there may be short-term peaks in one sense or the other, possibly causing some weather change (cf. the effects of the eruption of Krakatoa in the late 19th c.). We cannot predict the effects of a major caldera eruption, such as happened at Yellowstone ~600,000 years ago and which could happen again (at any time) within the next 50,000 years, but this could have a profound effect on global weather for a few years. Hope this helps. Brian Gary Bremer wrote: > What effect does volcanoes such as Mt. St. Helen�s have on the atmosphere > and environment? Dose not most of the plumes of ash, steam, and toxic gases > go up into the stratosphere where it effect the ozone layer? > > > Gary Bremer > > _________________________________________________________________ > Check out Election 2004 for up-to-date election news, plus voter tools and > more! http://special.msn.com/msn/election2004.armx > >