It's not a matter of if, but when!

http://en.wikipedia.org/wiki/Katla

In the past 1,000 years, all three known eruptions of Eyjafjallajökull
have triggered subsequent Katla eruptions.[14] Following the 2010
eruptions, on 20 April 2010 Icelandic President Ólafur Grímsson said
"the time for Katla to erupt is coming close ... we [Iceland] have
prepared ... it is high time for European governments and airline
authorities all over the world to start planning for the eventual
Katla eruption"[15].