Ashes, Ashes

And the planes don't fly.

Air travel chaos across the globe deepened on Friday as a vast, high-altitude plume of volcanic ash from Iceland spread further across northern and central Europe, forcing authorities to close airspace and ground airplanes to forestall potentially catastrophic damage to jet engines.

Or to the entire airplane, as volcanic ash will clog jet engines and the old rule of "engines turn or passengers swim" still applies. Two 747s in the 1980s had all four of their engines quit when the aircraft flew into a volcanic ash cloud, though both crews were able to restart them upon exiting the cloud. It's also not terribly good for the windows on the airplane to be blasted by volcanic ash.