Post 354 above sums up the situation neatly (if inadvertently!).
We appear to be in a Rumsfeld 'Unknown unknowns' situation and all the box-tickers who have no technical understanding of turbine physics/chemistry and no advice to work on do their customary knee-jerk and tick the box marked 'Airspace Closed'.
BUT....
- WHO is doing the physics / chemistry on particles in turbines? Or when are they planning to start?
- WHAT is the ACTUAL range of particle sizes, density per cubic metre, descent rate to ground, ...? (there seem to be a lot of unknowns in this category!)
- IS THERE a reliable method (apparently not current airborne radar) for detecting and assessing a 'dust cloud' that you're about to fly into?
- WHY is there little or no concern about OTHER 'dust clouds' that happen all the time: desert sandstorms, obviously, but there MUST be lots of very local clouds from industry, civil engineering, ..., that SHOULD affect LOW flying aircraft, especially helicopters. Don't remember ever seeing any reports of such damage....
Being in mind the report that last time this particular volcano had a serious eruption, it lasted 3 years, some detailed answers are quite important.