Vesuvius (Italy, NOT Iceland)
Well, today and tonight all across Europe: no planes! The airports are quiet, since all airspace of the UK, Ireland, Belgium, the Netherlands, Germany and Scandinavia is closed. And the one airport still in use is almost next to the cause of the closure of all the others: Reykjavik!
Now, if you don't have a clue of what I'm talking about and haven't watched the news today at all: Iceland is a volcanic island and about a month ago, there was a small eruption. Mostly lava, a few people got evacuated, it looked quite nice and that was the end. Until last night. When it erupted again. And there was no lava to be seen. The gletscher on the top melted (causing floods) and the top started exploding. That in turn caused a lot of rubble to be blown to pieces, shooting into the air and causing a massive ash-cloud. Which was blown by a northwestern wind towards Norway and Scotland. Where the wind was more northeastern, pushing it towards the south of the UK and the rest of Europe.
The volcano might erupt for a day, but it might be weeks or even months before it goes quiet again. And of course, there is the matter of the volcano's sister (or brother). A big sister (or brother) at that. Which is quite close and could cause even more trouble if that starts to go as well.