About flying through a volcano plume — it really is dangerous. Much of what a volcano spews is silica. It doesn’t show up on radar and you can’t see it. Fly through at 500 mph and it’s like getting sandblasted. It has been known to remove the paint from airliners...
Sand is also silica and sandstorms over North Africa dump many tons of the stuff into the atmosphere between Africa and the Caribbean. Aircraft fly through it all the time although the density is low. I don't think it is the presence of silica in the atmosphere but the density of silica that creates the problem.
Let alone what it does to turbine blades. You might as well throw a couple of buckets of bolts in.