@ Penko
Marconiphone, so just what do you call those KLM, Lufthansa and Condor pilots who are flying right now in search of a solution? It's nice to say that the ice may even make this ash even more dangerous (please give a link to this, not heard it before), but that does not answer the question: is there enough of the stuff up here to do any damage?
There was a post much earlier in this thread where one of the experts described that what happens is that when the lava hits the ice of the covering glacier: It freezes into glass; then the pressure builds up and it explodes - which shatters the previously frozen glass into sharp-edged shards of glass.
This makes it different from sand because (a) sand has rounded edges, and (b) the melting point of sand is way above the temperatures encountered in a jet engine, whereas the glass (more accurately, silicate) has a melting point considerably lower than the temperatures in a jet engine.
OK?