nimbev,
Mt St Helens caused some grief for the company I worked for at the time (Transamerica Airlines) although glad to say HQ dealt with that area, we at Gatwick dealt with Europe and the Middle East.
One of our L-382's took off from Mcloud AFB and within 15-20 mins had lost two engines and suffered "sand blasting" effects on the leading edges and windscreen. They landed back at Mcloud within 10 mins and of the other two engines one needed to be replaced as well.