Eyjafjalajökull has shifted from Plinan style eruptions (pulsating high-elevation ash plumes)to Strombolian eruptions (periodic blasts). Via Discovery News, shock waves propagate from blasts at the vent. I'm not absolutely certain what is causing this effect, but I'm guessing as the blast (very high intensity sound wave) moves outward, it pressurizes the air and increases its index of refraction. This would cause light to bend differently as it passes through the pressurized area. What I'm unclear on is whether this is decreasing the amount of light getting to and illuminating the background, a decrease in the amount of light reaching the observer after reflecting off the background, or a combination of the two. Whatever the exact cause, the rapid expansion of the ghostly shadows, followed a couple of seconds later by the plume from the blast that caused them, is quite eerie. Quite awesome, too.
Even though this looks more violent than what we've seen before, it's associated with less ash than last week's eruptions. Erik Klemetti's reporting at Eruptions confirms what I've been inferring over the last couple of days: the decreased ash and explosivity is probably due to a decreased presence of water as the ice melts back from the vent area. He also has an important venting of his own this morning, pointing out the maneuvering of corporate groups to portray the grounding of Europe's air fleet for nearly six days as an over-reaction on the part of governments and regulatory agencies.
Almost forgot... BBC also has a nice graphic workup on information on the recent eruptive sequence. Most won't be terribly new or informative if you've been following this story, but the third frame has a very interesting video clip illustrating how ash can melt onto and coat the turbine blades of a jet engine. The thing that really interested me- I already had a pretty clear idea of how that process occurred- was confirmation that as the blades cool, thermal stresses can cause quite a bit of the glassy coating to pop off. This had been my impression when I've read stories of ash-caused engine failures in the past, but I've never seen it stated bluntly and clearly. From everything I've read, no passengers have ever died as a result of engine failures in airplanes. There have been some very close calls though. To treat the very real danger to human lives, numbering in the tens of thousands, as inferior to the danger of losses of corporate profits, strikes me as exactly what I've come to expect from these companies. Repugnant, short-sighted, and seriously damaging to their long-term reputation and prospects.
A Bright Moon Impact
2 days ago