I just heard a news update on the radio. The main concern right now isn't this eruption - they don't think it will cause any further problems. But eruption at this site usually triggers a bigger eruption of the neighbor volcano - and THAT volcano is covered by several hundred meters of ice. Somewhat extreme version of "flash flood".
Trouble is - they expect this eruption, but don't know when. Could be days, could be months. And flood water could rush through populated as well as totally unpopulated areas.
Iceland is well organized and they are very though - and there aren't too many of them. Fewer people means less people in the way and less organization whenever something happens. As they just demonstrated, they've got their system up and running. Iceland is probably one of the best communities in the worlds to deal with catastrophes.