What with all of the news about the volcano, the newspapers and TV have repeated many times the story of the British Airways jumbo jet that lost all power when it flew into an ash cloud created by the eruption of Mount Galunggung in Indonesia in 1982. You'll remember the story of the heroics of the pilots who, having lost all four engines, decided to glide the plane into the sea but (after it had fallen from 36,000 feet to 24,000 feet) managed to restart the engines and land the plane safely. The point is that you can't see volcanic dust clouds on radar and that's why they've grounded all of the flights in Europe, because if the jets flew into the clouds then their engines would clog.
The events around one British Airways flight in 1982 reveal the potential dangers of this sort of dust... The passenger jet effectively turned into a glider... When all four engines on the Boeing 747 being flown by Captain Eric Moody shut down at 37,000ft, he hadn't a clue why.[From BBC News - When volcanic ash stopped a Jumbo at 37,000ft]
This story always reminds me of my experiences on the ground. I was living in Bandung in central Java when that volcano went off. And when the ash cloud reached us, it was honestly one of the most unusual days of my entire life. We'd been told that the ash cloud might come but I don't remember that having any connotations. I don't remember thinking anything about it, other than that I'd never seen a volcanic ash cloud. When we woke up in the morning it was pitch black. I mean absolutely black, not like dark at night when there's still a little moonlight or starlight to see by. I mean it was absolutely pitch black, the ash blocked out the sun completely. Visibility out in the streets was maybe 50 feet maximum. You couldn't see the dust in the air right in front of your face but you couldn't see 50 feet. It was like being in fog where you can't see the fog right in front of your face.
Since we didn't know what else to do, we got into the car and slowly navigated our way to the office. Everyone was driving very slowly with their headlights on. I can't remember ash on the ground. It wasn't like snow where it was piling up on the side of the road, I don't remember that at all. I just remember a coating of dust on everything. When we got to the office, we were issued with face masks. They just covered your nose and mouth with a sort of cotton pad which was held in place with an aluminium frame and some elastic. I actually hadn't found it difficult to breathe but it was really shocking after you put the masks on because after no more than a few minutes you could see a red film building up on the face mask where the volcanic dust was building up on the cotton instead of, presumably, going into your lungs.
It was a really strange day to spend a day, a whole day, in the pitch dark. And I can still remember how it felt sort of other-worldly to be walking round in total darkness in the middle of the day. The volcano didn't seem to affect anything in the sense that it didn't seem to stop cars from running or computers from operating. We were running some DEC mini and some early PCs (XT?) with Microsoft's now long-forgotten version of Unix called Xenix. Perhaps equipment was just more robust in those days, jet-engines excepted.
While in a reminiscing about volcanoes mood, I've also upload three pictures of my visit to Anak Krakatoa ("child of Krakatoa") in 1983. It had erupted a couple of years earlier but was quiet when we got there so we just made our way up it! It was hot, but not intolerable, and it was quite exciting to stand on the top.