Not exactly volcanic, but...

Not many details yet, but the USGS Earthquake list shows a M7.2 earthquake ~25-30 km from Christchurch, New Zealand. I'll post more details as I find them, but here is a Google Map of the epicenter - UPDATE: the refined location puts it further from Christchurch, to the northwest. The earthquake appears to be relatively shallow - 16-30 km deep, but that is a preliminary estimate. I don't know much about the tectonics/structure around Christchurch, but you can see that Christchurch is to the south of the termination of the subduction zone between the Australian and Pacific plates. The historic seismicity for the area implies this isn't a likely location for a big earthquake. There is no active volcanism on the South Island of New Zealand (that I know of ... anybody know better?)

UPDATE 9/4: If you are looking for the best and most indepth coverage for the science aspects of the earthquake, head over the Highly Allochthonous. It is remarkable that no one died in this earthquake considering its magnitude and location. You can see the video of the damage on the NZ Herald site - lots of examples of surface displacement - and other updates as well.