Just as a point of order.
The material being ejected from this volcano is not in someway completely different to other volcanoes as some have said. Most rhyolitic rock is about 70% silica - and that is believed to damage aircraft engines. The rest is commonly mixtures of quartz, feldspar, biotite and hornblende along with some other minerals I have clearly forgotten. But the crux is the the SiO2.
If you read the contributions from volcanologists on this thread or indeed if you do some research yourself, or have a basic understanding of eruptions, what they are saying is that this is a specific type of eruption. One which involves water/steam (phreatic eruptions/phreatomagmatic eruptions respectively). This is because the Volcano sits beneath a large Glacier.
The rapid thermal contraction which occurs in these instances produces an explosive eruption, which in turn produces particles of ash in sizes from clay to sand which can be thrown high into the atmosphere and in this case inconveniently into a jet stream bound for Northern Europe.
Please desist with the "but this is magical ash" comments. It is not accurate.
Moreover this is not the first explosive eruption to have occurred.