Is there anything particularly unusual with this type of behavior under Katla?
More info on Katla here.
http://www.csmonitor.com/Science/2010/0418/Iceland-s-Eyjafjallajoekull-volcano-is-nothing-to-Angry-Sister-Katla
When, not if, Katla goes off Europe is going to feel it much worse than what they received from E-15 since Katla is a much larger volcano.
Probably represents magma movement, probably some of the precursors that scientists have been monitoring