Ash Thursday

It's not a new Catholic holiday, but a reality in the British Isles:

Ash clouds from Iceland's spewing volcano disrupted air traffic across Europe on Thursday as authorities closed air space over Britain, Ireland and the Nordic countries. Tens of thousands of passengers were stranded as flights were canceled and it was not clear when it would be safe enough to fly again.

Britain's Civil Aviation Authority said non-emergency flights would be banned in all airports until at least 6 p.m. (1700 GMT, 1 p.m. EDT). Irish authorities also closed their air space for at least eight hours, along with closures by aviation authorities in Denmark, Norway, Sweden and Finland.

The move shut down London's Heathrow airport, a major trans-Atlantic hub which handles upwards of 1,200 flights and 180,000 passengers per day. The closure also affected London's second- and third-largest airports, Gatwick and Stansted. Shutdowns and cancellations spread to France, Belgium, the Netherlands, Denmark, Ireland, Sweden, Finland and Switzerland.

You might think the problem is a visibility issue with all the ash in the air, but that's not it.  Ash is basically pulverized rock and glass and you can't run that stuff through jet engines without doing real damage.  There have been cases where aircraft engines were destroyed by ash clouds, and in two instances 747s suffered flame-outs on all four engines after encountering an ash clouds, one over Indonesia and another over Alaska.  You want to stay out of that stuff.