Hi all,
What an interesting discussion you've started here. It's very unexpected as plume dynamics (or just plain appreciation) tends to be overlooked by many meteorologists, yet can have such tremendous local and global climatic repercussions. The majesty of large explosive eruptions can be extremely hard to resist and you'd certainly find volcanologists a similar breed to many storm-chasers. You're doing a great job of displaying some of the classic eruption photos here and I've noticed a few queries appear that I'd be keen to discuss.
I saw Jimmy mention the conical formation in the Reventador photo. To me, this looks like ash falling from the upper plume, in front of the main eruption column and fining out during descent (note the diffuse lower edge). Reventador looks to have experienced a minor eruption in 2007, although the last official period of activity spans 2004/05. The photo shows Strombolian-style activity, as opposed to the extremely vigorous Plinian activity illustrated in many of the other photos. Strombolian eruptions are pulse-like in character as volatile gases build under a cool, hardened 'slug' of material in the volcanic edifice, with the eruption occurring once the gas pressure exceeds the deformation threshold of the magma. This kind of behaviour certainly could create a situation where you'd witness a small plume with lofted materials sinking in close proximity to the main updraft. With your experienced eye, would you consider this feasible?
Harley, aside from recounting enough classic eruptions to make a hazard scientist gush, was curious about the effects of the 2006 Tungurahua eruption upon the Australian climate. I think you may be scratching on this correlation Harley, since the eruption was not strong enough to produce stratospheric injection of aerosols. Without that, highly-soluble sulphur dioxide would rapidly be washed out of the local atmosphere as acid rain and the climatic effects would only be local. You mentioned several significant climate-influencing events; Laki, Tambora, El Chichon, Pinatubo, all of which had colossal eruption rates, towering Plinian eruption columns (some in excess of 40km, which is pretty staggering for those convection experts here) and high aerosol content. All are considered to have significantly altered global climate and stratospheric injection of material of high aerosol content is the common factor.
Something I find fascinating are the reports of incredible lightning emanating from eruption columns and pyroclastic flows. Volcanic lightning is seldom researched or even mentioned in the academic literature and is a topic befitting of discussion here. I've always wondered whether the intensity of the strokes would differ from those formed in thunderstorms, given that volcanic lightning arises from collisions of fine ash. I'd imagine that there would be little difference because the path would remain the same i.e. the resistance of the air would be the factor to overcome and a flash would occur once this was breached. Any ideas?
Cheers,
Olly
