The harmonic tremor that started yesterday in Katla volcano continues. It is however at less strength then yesterday. Often there are small earthquakes following it. They can be poorly observed on my Heklubyggð geophone. Few earthquakes have happened during this unrest. GPS data is unreliable, as it has not been updates since mid December 2011 (why that is I do not know). At current time it seems that this harmonic tremor is dropping down at the moment. It is impossible to know for sure if this is the end of this tremor in Katla volcano for the moment or not.
There are now two possible reasons why this is happening. This might be an increase in hydro-thermal activity in north part of Katla volcano. Second reason might be that this is magma moving around inside Katla volcano at depth, then out visible effects on the surface. That is earthquakes have not happened following this event to any extent. There have only been two registered earthquakes so far. There location is both poor and depth poorly located. It has been my experience that following smaller event of this type there is generally an earthquake swarm in Katla volcano caldera. The time is is from from this type of event to take place until the earthquake swarm takes place differs a lot.
Last minor eruption that took place in Katla volcano was on 6. September 2011. My blog posts about it can be found here. It was believed at the time this was water. But today I now think this was an small eruption rather then water flooding under Mýrdalsjökull glacier.
Both blog posts are from 6. September 2011.