Earthquake swarm in Iceland raises threat level on Bárðarbunga volcano

http://all-geo.org/volcan01010/2014/02/a-history-of-ash-clouds-and-aviation/
The orange areas in the barcode-like diagram below show all the periods in which volcanoes in Iceland were erupting.  The data came from the Global Volcanism Program.  It’s a fairly regular occurrence, as you can see.  On average, as I explained in my first ever volcan01010 blog post, there is an eruption in Iceland about every 5 years, with 3/4 of them being explosive.  The wind blows towards the UK about 1/3 of the time, so you could expect a direct hit from an ash cloud about once every 20 years.
The Surtsey and Krafla Fires eruptions stand out for their long duration.  Surtsey, in particular, is interesting because the eruption produced a new island in the north Atlantic, with ash-rich explosions driven by hot magma boiling the water of the ocean.  It lasted three and a half years.  What would happen if a similar eruption began now?
I’ve marked the three most powerful explosive eruptions, Hekla 1947, Eyjafjallajökull 2010 and Grímsvötn 2011, with bold lines.  These produced much more ash than the others.  It is pure luck that there was such a long gap between them.
http://all-geo.org/volcan01010/wp-content/uploads/2014/02/Air_traffic_vs_eruptions_01-1024×677.png
Check out the article for more…

They are evacuating now, seems a 4.5 quake happened. They are afraid of a pyroclastic flow with all the ice at the top causing mud flows. There have been thousands of quakes in the last four days. But it is an isolated region, but might blow and effect air traffic in the region.

I’ve been pondering why these large numbers of small to moderate magmatic quakes (now past 4,000) is not leading to vertical rise in close by GPS geodetic measuring sensors but rather only a horizontal dilation across the associated fissure complexes in a NE and SE direction of extension.
The dilation is easily explained by intrusion and combined magmatic and effectively tectonic opening of the tectonic rift the fissures represent, with full through crustal dyke-swarm emplacements, which always occur at such rift surfaces when they begin to open.
But there is a very puzzling lack of vertical motion here and there is no clear explanation of its failure to be expressed in a proportional surface rise.
This is a serious complication in interpreting what this system is doing, as ground displacements upward are typical of a magma body that’s infiltrating and rising while pressurising its confinement via decompression as it exsolves its entrained molecular gas components, which exponentially increase the confinement pressure, even as the static and overburden containing pressure is also decreasing.
So ordinarily this situation will be resolved by inducing moderately large magmatic quakes.
Which is what occurred in 1996 in this same system, except the quakes did not lead to vertical movements indicating pressure displacements prior to the eruption that occurred hours later. This 1996 behaviour at Bardarbunga was very peculiar, for how can there be no ground displacement from very strong shallow shocks and a remarkably strong series of shocks in the swarm that followed?
It made no sense, in much the same way the present measured situation makes little sense. Why this lack of ground rise? The problem becomes clearer with reference to this:
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Magma surge towards the surface would be very powerful – 20th August 2014
Kristín Vogfjörð, research director at the Icelandic Meteorological Office, says that the current seismic activity at Bárðarbunga is many times more powerful than any on record for the site. “It’s very powerful,” she says. For comparison she notes that thousands of quakes have been measured at Bárðarbunga in the past week, but in the Gjálpar [Gjlap] eruption in 1996 they were only a few hundred. … “While this is going on, it may never reach the surface. But we still need to keep an eye on it because the volume of magma is incredible,” she adds. …”There is no indication that it’s moving further up than that. But if it were to happen, it would happen very quickly,” Kristín states.​
http://www.visir.is/magma-surge-towards-the-surface-would-be-very-powerful/article/2014140829927
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So an “incredible” volume of magma has been literally rushing through the Bardarbungar conduit into the fissure-swarm complexes around it (and past where Gjlap occurred), and there is again no rise in ground level. Well, except at Grímsvötn 30 km away, where the protruding outcrop is being pushed upward most! Wot?!
The geometry of that is so odd. It would be easy to ignore that and just move on, but it’s telling us something vital about this system, especially with reference to what occurred previously. The instrumentation is working and it is telling us something.
To set the scene of the previous occurrence:
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On September 29th, 1996 at 10:48 an earthquake of magnitude 5 on the Richter scale was detected within the Vatnajökull icecap in SE Iceland. This event was followed by an intense earthquake swarm with a large number of small events with intermittent larger quakes of magnitude 3-4 on the Richter scale.
http://earthice.hi.is/gjalp_eruption_vatnajokull_309_1310_1996
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It erupted hours after this without further seismic warning. And curiously, Grímsvötn, close by, erupted through the icesheet on its SW flank only years later. Was there a magmatic connection here? Some authors have argued there isn’t a direct connection between the two volcanos
But yesterday it was demonstrated for the first time, seismicly and magmaticly that there is a connection between Bardarbunga and Grímsvötn calderas. From Volcano Cafe yesterday:
Bárðarbunga loves Grimsvötn = True
http://volcanocafe.wordpress.com/2014/08/20/bardarbunga-loves-grimsvotn-true/
So magma sharing and mixing is possible, as are sympathetic eruptive sequences due to fissure flows. Pressure is apparently not a problem, the system appears to not highly pressurise before eruptions. It apparently has ‘give’, for as extension from intrusion in one part of is taking place, it can be can be accommodated via the less filled chambers and fissures flexing and changing volumes to allow the new local inflows, without over pressurising the vast network, nor the point of inflow either! The result is the ground does not rise prior to the eruption at and near Bardarbunga.
This is a real problem for authorities as almost all other volcanos would exhibit accelerating vertical movement prior to eruption, but at Bardarbunga you only get the quake swarm and tremor and no ground rise indication of magma rising to erupt – in 1996 it just happened. Yes, they had the quakes and an eruption was considered immanent, but the lack of ground distortion and lack of implied magma rise and lack of implied pressurisation took them by surprise. So much so that at least one paper examining this was written about how to explain it.
Below is the partial abstract text from the paper and webpage created to draw attention to how peculiar this is at Bardarbunga, namely, how can so much energy release, materials injection result in so little effective signs of displacement before the eruption occurred?
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“Abstract A volcanic earthquake with Mw 5.6 occurred beneath the Bárdarbunga caldera in Iceland on 29 September 1996. This earthquake is one of a decade-long sequence of M5 events at Bárdarbunga … This indicates the absence of a net volumetric component, which is puzzling in the case of a large volcanic earthquake that apparently is not explained by shear slip on a planar fault. A possible volcanic mechanism that can produce an earthquake without a volumetric component involves two offset sources with similar but opposite volume changes. We show that although such a model cannot be ruled out, the circumstances under which it could happen are rare. …”
http://rses.anu.edu.au/~hrvoje/Bardarbunga.html
http://rses.anu.edu.au/~hrvoje/Tkalcic_etal_BSSA2009.pdf
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So, some unusual connective geometry and cavity arrangements and horizontal flexibility exists within this network which does not result in uplift before eruption – it is an extensional tectonic triple junction so of course the stress/tension vector is always to extend and expand the crust and accommodate new magma under a shallow caldera crustal roof. So no matter how much magma flows in, it will not pressurise, it will just extend.
An eruption will thus occur when the inflow rate is so high that the extension response is lagged and can not accommodate it quickly enough, and pressurisation and eruption occur anyway. In which case the eruption will be very sudden and degassing magma vector becomes directed upwards at that point, for it’s then much easier to go upward, than recompress gas to move sideways. The same can occur if the magma suffers a sudden gas decompression, it will immediately go where the shock confining pressure is least – upwards if the magma is already shallow enough.
So, the rushing magma influx implied by intense swarm and tremor is all the warning you get, the magma may shows no obvious pressurisation indications, no sign of a rise and no ground uplift before it erupts. So where Kristín Vogfjörð, research director at the Icelandic Meteorological Office says above that there is no sign at all of magma rise to the surface, the signal looking for that would typically indicate those processes, do not seem to be present at Bardarbunga.
So this system can decork without any signs that that magma is about to blast skyward. But Kristin does go on to say, “… But if it were to happen, it would happen very quickly,” Kristín states.”​
She is well aware of the peculiarity of Bardarbunga to pre-pressurising (implied from ground movement) in 1996 given she specifically referred to the circumstances of that eruption. She also said, “… For comparison she notes that thousands of quakes have been measured at Bárðarbunga in the past week, but in the Gjálpar [Gjlap] eruption in 1996 they were only a few hundred. …”
Hopefully they expressly see that the two situations are both showing no prior sign of net vertical displacement and implied pressurisation despite numerous powerful quake swarms indicating substantial magma influx.
But where is that magma currently going? Firstly into Bardarbunga itself then re-charging the fissure swarm feeder chambers, and the quakes in Kverkfjöll, including the mag 4.5 at 6 km depth under it two days ago indicates excess magma is going into it. It is also flowing into the fissure-swarm feeder cavity south west of Bardarbunga as well. It is also feeding the area north and NNW of Bardarbunga as well.
And at Grimsvötn its main magma chamber is already partially full of magma so the extra pressure coming in from Bardarbunga’s influx is causing the magma level in Grimsvötn to back up and rise again after its 2011 eruption.
Hence Grimsvötn is the only GPS station that is actually rising, as all the others as simply horizontally extending.
As a result, any eruption as this enormous system continues to fill can become especially large and episodic, as well as stir sympathetic eruptions at several volcanic centers incoming years.
Alternatively the magma influx slows and stops and it settles down and just plops off eruptions progressively over the next century or so.
But the potential now exists for something very nasty to take place with no further notice, as extensional collapse and opening of chamber structure is entirely possible as the crust continues to dilate.
It all comes down to how much longer this goes on, ~130 hrs so far, and is actually visibly intensifying:
http://volcanodiscovery.com/bardabunga-earthquakes.html

Warning! It is believed that a small subglacial lava-eruption has begun under the Dyngjujökull glacier. The aviation color code for the Bárðarbunga volcano has been changed from orange to red.
http://en.vedur.is/earthquakes-and-volcanism/earthquakes/vatnajokull/
There have been 14 Mag. 3+ quakes in the past 72 hrs. (4 in the past 6 hrs.) About 10:00 Saturday, there was an abrupt rise in the Magnitude of the quakes from the high 1s to the high 2s.
About 48 hrs ago, a second area, WSW of the first, at about long 17.4 W. The largest quakes are happening here.
http://baering.github.io/
A small eruption has started near Bardarbunga. Source
http://www.ruv.is/frett/small-eruption-near-bardarbunga
A small sub-glacial volcanic eruption has started near Bardarbunga volcano, under the icecap of Dyngjujökull glacier in the northern part of Vatnajökull glacier, according to the Icelandic Met Office. All air traffic is now prohibited in a large radius around the volcano.
updated on 23 August 2014, at 15.13 GMT.