The Icelandic problem- part of the Atlantic ridge at the conjoin of the N American and Euro plates seems to have a 140 year cycle and it looks as if it is stirring up once more - looks like more 'Staycations' and cruises then.
this volcano has a twin sister not very far away and the last three times this one has erupted, the other, bigger one has erupted too. It's not so much the holidays that would be the problem, we get a lot of goods imported by air, particularly foodstuffs. I can envisage a price rise or the disappearance of lots of items, particularly fruit, should flights be significantly hampered.
20 years? That is but a blink of an eye in terms of the earth's history, it is possible you could easily put another nought on the end of that 20 years, I sincerely hope not, but how long is a piece of string?
A lot of manufacturers/suppliers seem to jumping on the volcano bandwagon. I've been waiting for delivery of a digital camera for the last six weeks and, on phoning the company last Saturday, was told, "It's all due to the volcanic ash, sir"