In response to a comment on the previous entry, about flight cancellations in Argentine Patagonia, I wrote to Patrick Smith, a commercial airline pilot and author of Ask the Pilot, about the effect of volcanic ash on airplanes. Patrick is also the air travel columnist for Salon.com.
His reply to my question was the following:
"Volcanic ash can be very troublesome and occasionally dangerous to commercial airliners. It can scour up a plane's exterior, turn windshields opaque, and cause serious engine damage. A British Airways 747 once lost all four of its engines after an ash encounter over Indonesia. (Three of the engines were eventually re-started and the plane diverted safely to Jakarta.) A KLM 747 suffered a similar incident flying over Alaska. Ash is invisible to a plane's radar, making it hard to detect and avoid, particularly at night."
"Nine volcanic ash advisory centers (VAAC), positioned around the world, issue regular updates on ash plumes (position, severity, etc.) for commercial flights. The VAAC for South America is headquartered in Buenos Aires."
Presumably the Buenos Aires VAAC is well situated to make the call on flights into Patagonia, but there are no active warnings posted on its website.