During the last couple of days there have been a few small, but still noteworthy earthquakes along the Bárdarbunga fissure swarm. I thought we should bring them to light and put them slightly into context, but first a brief background.
The Bárdarbunga fissure swarm is the longest of Iceland’s fissure swarms spanning 180 kilometers to the south from Bárdarbunga, and about the same distance to the north. It has since de-glaciation been the most prolific in having rifting fissure eruptions with at least 5 known eruptions along the southern part of the fissure swarm (Veidivötn/Vatnaöldur) and at least 3 in the northern part of the fissure swarm.
It contains at least two active central volcanoes, Bárdarbunga itself (a massive caldera volcano) and Hámarinn. To the north you will also find the seismically active Kistufell table top volcano, and Iceland’s largest shield volcano, Trölladyngja.
The fissure swarm is responsible for the largest known historical flood basalt eruption, the more than 30 cubic kilometers Thjorsáhraun. The fissure swarm stands for about half of the Icelandic lavas during post-glacial times.
During the last 10 years persistant uplift have been measured at both the Hámarinn and the Jökulsheimar SSW of Hámarinn, lately there have also been more un-localized uplift around the fissure swarm.
On Sunday two deep earthquakes took place under Trölladyngja at a depth normally associated with magmatic movement. They could be associated with either movement of magma up into a deep chamber, or production of fresh magma. One should though note that they were small in magnitude.
Sunday 16.06.2013 20:23:11 64.893 -17.188 18.5 km 0.7 99.0 2.9km E of Trölladyngja
Sunday 16.06.2013 20:22:58 64.879 -17.176 18.6 km 0.8 99.0 3.9km ESE of Trölladyngja
The likelihood of this entailing a future eruption at Trölladyngja is very small; it is more a symptom of erratic behavior along the Bárdarbunga fissure swarm as it is slowly inflating at depth.
North of Veidivötn
A series containing 4 small earthquakes took place at shallow depth at the northern end of the Vatnaöldur fissure and northwards under Vatnajökull. These earthquakes were not magmatic in any way; instead they were caused by isostatic rebound relieving pressure. It is though a sign of mounting strain in the area.
Monday 10:51:40 64.282 -17.665 5.9 km 0.4 99.0 23.3 km SW of Grimsfjall
Monday 09:32:05 64.309 -17.782 0.1 km 1.4 99.0 19.8 km S of Hamarinn
Monday 05:36:44 64.320 -17.721 0.1 km 2.1 99.0 19.1 km SSE of Hamarinn
Monday 04:36:58 64.219 -18.121 0.1 km 1.7 99.0 17.5 km NNE of Laki
As time goes by and the strain increases we will see more of these earthquakes affecting the Bárdarbunga fissure swarm. In the beginning the picture will though be confusing, but as time goes by I fully expect the picture to get clearer, but remember, we are looking at quite some time before something will happen. Perhaps it will be as short as a few months, but more likely years, or even decades, and in the end a whole lot of nothing may happen.
I seem to have grown slightly prophetic as I am nearing old age. A couple of hours after posting this a small lineament earthquake swarm took place almost due east of Bárdarbunga volcano. All of the earthquakes were small, but one of them was at a depth indicating magmatic movement, 21.1km. This is either at the extreme outer edge of the Bárdarbunga fissure swarm, or inbetween this swarm and the Grimsvötn fissure swarm. This shows how large the area affected by the magmatic pulse is. Right now we have to wait for about 3 to 5 days to see how the GPS patterns for the area will be affected.
Short update on the update. Thanks to our hardworking friends at the IMO night shift we now know that there were 3 earthquakes deeper than 20 km (21.0, 24.3 and 21.1). If you check the link the lineament of those earthquakes is looking even more interesting.