I was just there a few weeks ago, and the locals were expecting an eruption in the not too distant future (months or years); they were talking about evacuation plans, gathering points and such.
The eruption is small now but that this could become serious isn't an overstatement.<p>I can't recall the details now but I've reviewed the evacuation plan (but can't find it now) used for the area.<p>Once Mýrdalsjökull starts erupting it's only a matter of hours before the meltwater starts flooding across the lowlands. It'll be a glacial mudflow many meters high initially and the water/mud should be at around 1 meter at Hvolsvöllur ~40 kilometers away.<p>Earlier Hekla eruptions have caused global cooling for a few years. Wikipedia has more information on it.