I saw this this morning.
http://www.timesonline.co.uk/tol/new...cle7101084.ece
The fear is that the previous 3 recorded eruptions at Eyjafjallajökull has set off the much-bigger Katla volcano. The last Eyjafjallajökull eruption was estimated to be just 0.1 cubic Km in volume. The 1980 Mt. St Helen's was 1 cubic Km. The 1781-83 eruption at Laki was 14 cubic Km. There's no reference to how potentially big Katla could be but it's bigger than Eyjafjallajökull.