Aircraft and volcanic ash have a history - and the aircraft tend to come out on the loosing end.
Two examples:
Speedbird 9:
https://en.wikipedia.org/wiki/British_Airways_Flight_9
KLM 867:
https://en.wikipedia.org/wiki/KLM_Flight_867
While both ended happily, they were both close calls, and the aircraft damage in both cases was in the millions of dollars.