This article is going to be updated as activity continues in Katla volcano today on 29-July-2017. If an eruption starts (big one) a new article is going to be written for that event.
Overview of the activity during the night and today
It seems that during the night a minor eruption took place (this is just my view). This based on harmonic tremor pulse that appeared in Katla volcano after midnight, the source of the activity seems to be north-west part of the caldera. Possibly where a magnitude 3,0 earthquake had taken place at 00:48 UTC. Harmonic tremor remains unstable and above background levels, at the moment however it seems that current harmonic tremor when this is written is due to glacier flood pushing it self from under the glacier. The water that is moving under the glacier is few hours away from (at best) from appearing in glacier rivers that come from Katla volcano.
Harmonic tremor in Austmannsbunga in Katla volcano at 13:04 UTC. This image shows ongoing activity in the tremor. This is mostly high frequency tremor and that is interesting. What that is not known. Copyright of this image belongs to Icelandic Met Office.
Harmonic tremor in Goðabunga at 12:09 UTC. It clearly shows the night minor eruption and ongoing harmonic tremor. The harmonic tremor is however a lot less visible now on Goðabunga. Copyright of this image belongs to Icelandic Met Office.
Harmonic tremor as it appears on Rjúpnafell (SIL station). This station is at more distance from the source of the harmonic tremor pulse and shows a weaker signal as a result. The night minor eruption is also clear on this SIL station but current harmonic tremor is less visible, it does appear but at much lower level. Copyright of this image belongs to Icelandic Met Office.
Katla volcano has been moved to yellow alert. It is now possible to watch the glacier flood live from here (Rúv.is). Currently the glacier flood is getting smaller, but that might only be a temporarily thing if more water is on its way from Mýrdalsjökull glacier. There has also been a drop in conductivity for now in Múlavísk glacier river.
Announcement in English on Rúv
This article is going to be updated as needed today.