When the Eyjarfjallajokull volcano let go in April 2010 I was the last flight out of Frankfurt before they closed the airspace due to the threat of volcanic ash. On April the 16th in SQ 747-4 (9V-SPE Flight SQ26 FRA to JFK) we were airborne with only 20 minutes to spare with the Germans closing the airspace behind us. The French denied us entry through their airspace so we had to track via Spain and cross the Atlantic just North of the Azores. On arriving in New York we were subsequently stuck there for a week. From memory, they closed the Atlantic airspace on all tracks North of N48 degrees.
I understand the Geologist's call it a 'Super Volcano.' The eruption was not the main bit apparently, and if 'Mummy' goes bang it will be a very big one. I still can't pronounce it and my spell-checker is not happy either.