Monaco Bank: An Unstudied European Volcano

Monaco Bank is a submarine volcano located in the Azores Island Arc. The volcano was constructed on regional tectonic trend connecting the active volcanic island of Sao Miguel (5 volcanoes) to the now extinct Santa Maria Island. Like many Azores volcanoes, the volcano is rift-dominated, built on a NW-SE-trending fissure 20 km south of the western tip of Sao Miguel Island. The volcano therefore has an elongated profile (much like San Jorge Island, Azores) rising to within 197 metres of the sea surface.

Photo showing the sea floor around the Eastern Azores. Monaco Bank is the ridge extending south from Sao Miguel in the bottom centre of the image. Don Joao de Castro Bank rises from the sea floor between Sao Miguel and Terceira. Photo from Santos and Tempera et.al, 2010.

Two eruptions have been documented from Monaco Bank. The first, in 1907 was only discovered because it broke an underwater telegraph cable. In 1911, a second eruption occurred when underwater phreatic explosions created water jets the broke through the sea surface.

The volcano is unusual for a European volcano as it has never been studied. Unlike nearby Don Joao de Castro Bank seamount volcano, whose morphology and hydrothermal vent communities have been studied well.

Lucas Wilson

REFERENCES:
R.S. Santos, F. Tempera, A. Colaço, F. Cardigos, and T. Morato. 2010. Mountains in the Sea, Spotlight 11. Dom João de Castro Seamount. Oceanography, 23:200–201, ( http://dx.doi.org/10.5670/oceanog.2010.83)

NOAA. 1986. Catalog of Submarine Volcanoes and Hydrological Phenomena Associated With Volcanic Events, January 1, 1900 to December 31, 1959. 45 p

Siebert L, Simkin, T. 2002-. Volcanoes of the world: an illustrated catalog of Holocene volcanoes and their eruptions: Smithsonian Institution, Global Volcanism Program. Digital Information Series GVP-3, (http://www.volcano.si.edu/world)

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From Global Tectonic 3rd Ed.

“The stability of the boundaries between plates is dependent upon their relative velocity vectors. If a boundary is unstable it will exist only instantaneously and will immediately devolve into a stable configuration… A more complex and potentially unstable situation arises when three plates come into contact at a triple junction. Quadruple junctions are always unstable, and immediately devolve into a pair of stable triple junctions.”

There are three essential types of junctions that make up plate boundaries at triple junctions. Trenches, Ridges, and Transform faults. (convergent, spreading, transform). Whether a junction is stable or not, depends on the movement rates of the various plates that make up the junction. Some orientations are completely stable (Ridge, Ridge, Ridge) others are completely unstable (Transform, Transform, Transform). Others have special conditions in which they are stable, or else the junction will migrate down one of the interfaces until it meets a stable condition.

A good example of that is the San Andreas. When the Farallon plate made its final plunge under the North American plate, two types of triple junction formed. (“A quadruple junction existed momentarily at about 28 Ma, but this devolved immediately into two triple junctions “) A ridge-transform-trench, and a transform-transform-ridge. Each one propagated North or South until it met up with the Mendocino Fracture zone (a transform) or the Murray Fracture zone (another transform). Once two of the three legs of the junction formed a strait line, the junction became stable. (Over time, the Murray FZ has effectively become “locked” and other dynamics further south in the Gulf of California have taken over) Another example of the dynamics of these forces is the Alpine Fault of New Zealand. Though not a full on triple junction system, two separate plates are colliding head on. North of the Alpine fault the Pacific plate is being sliced and part of it drops under the Australian Plate (Zealandia) and south of the Alpine Fault, the Australian plate (Zealandia) is being sliced in two. In each case, the Alpine fault is the intermediary and has become the transform fault between the two opposing trenches. Flower Structures dominate the Alpine fault as portions of it lock and fail over time.

The Azores Triple junction is the intersection of the MAR, and the Terceira Rift. As a transform-transform-transform system, it is one of the most stable configurations that you can get. The problem is that as the dynamics of the three major plates come into play, they can easily upset the balance and turn any part of that junction into an unstable configuration. Once that happens, the junction will migrate around trying to find equilibrium. Toss in a hotspot, it turns into a mess. On geologic timescales, it is quite easy for one massive plate to suddenly change direction. This is evidenced by the Emperor Seamount chain and the Hawaiian island chain. About 45 to 48 million years ago the Pacific Plate changed motion by about 70°. Any plate margin or junction that it was part of would have felt this sudden shift in the prevailing forces.

Now when you take a look at the dynamics at the Azores, it’s pretty easy to see the lasting effects of changes in plate movement.

Take note of where the Monaco Bank is at on this plot. At one time, the East Azores Fracture Zone was likely the dominant transform fault all the way over to the MAR as part if the Pico Fracture Zone.

When you take a look at the dynamics at the Azores, it’s pretty easy to see the lasting effects of changes in these dynamics. From Global Tectonics about Ridge, Ridge, Transform: “Unstable, evolves to FFR” (Transform, Transform, Ridge) Or, as seems to be the case for the Azores, snap off a piece of crust and make it a Ridge, Ridge Ridge junction.

Supporting Material by GEOLURKING.

“Global Tectonic 3rd ed” Keary (deceased), Klepis, and Vine. John Wiley & Sons Ltd. ISBN 978-1-4051-0777-8

Upper mantle structure beneath the Azores hotspot from finite-frequency seismic tomography Yang (2006)

Dynamics of Mantle Flow Around The Azores Triple Junction: Constraints from bathymetry and gravity data Sankar Thesis Paper (2009)

UPDATE:

Name that volcano riddle by Suzie!

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Out of chaos came darkness. Out of order comes enlightenment.

The Icelandic Hotspot Hypervolcano™ – Why old traps won’t erupt again

Photograph by Jeff Shea. A range of north Greenland shield volcanoes eroded by glacier ice so that they more remind of a range of strato-volcanoes.

Earlier today commenter Lucas Wilson asked me about volcanism in Greenland. So, I thought I should write a short piece on what once used to drive the volcanism there.

But let us start with what we today call the Icelandic hotspot. In here we have a tendency to talk about large volcanoes now and then, and sometimes about what is called “super volcanoes” in the media. But, the fact is that Iceland is both the largest volcanic structure on the planet, and also by far the oldest active one.

Let us start with largest. Iceland stands for between one third and half of all the magma on the planet during the last 250 million years. The rate of lava produced is fairly prodigious. Also, few know how long this has been going on. The answer is that it all started far before Iceland was born. Time for a history lesson.

Iceland was born as the Icelandic Hotspot moved close to the Mid Atlantic Rift; Iceland was born from the mid parts to the west and the east. This is as a function of the hotspot giving extra magma to the normal volcanism of the MAR, and thusly building the volcanic edifice known as Iceland as the MAR rifts apart.

Photograph by Ansgar Walk. Trap formation eroded by Glaciers, Ice age glaciation, and coastal erotion. Baffin Island.

Okay, now to the age thing. The Icelandic Hotspot is one of the really few surface expressions on the planet that is stationary. I know, the hotspot per see is not visible, but its effects are. So, as the continents and plates have fun surfing around bumping in to each other they slide over the poor hotspot.

A few tens of millions of years ago it was a part of the North American plate that slid over the Hotspot, and as that broke apart magma pushed through and created Greenland. As the now archipelago of Greenland slid away it lost its capacity to have eruptions pretty permanently.

Before that it was Newfoundland that popped up as it slid over the hotspot. And before that we had the same hotspot creating the largest Large Igneous Province on the planet, the North Arctic Igneous Province (NAIP). Before that Labrador and Baffin Island slid over the NAIP, and that put us at about 95 million years ago. And 130 million years ago it created the Alpha Ridge. Any  super volcano will have an inferiority complex to that eruption.

Before that and even further down in time it was known as the Siberian Traps, the largest on land eruption. And now we are back 250 million years in time. Before that things get a bit harder to track.

Photograph by Jxandreani, wikimedia commons. This is a part of the Putorana-Norilsk Deposit.

Here comes an interesting thing. What is today known as the Icelandic Hotspot has been conveying about the same amount of magma since the Siberian Traps. Give or take the eruptive rate has constantly been around 0,5 to 1,5 cubic kilometer per year since day one. And as we all know the average erupted material is only 1 in 20 of the magma that comes up. The rest stays as intrusions or inside magma chambers. So, on an average year the Icelandic Hotspot will loft up 20 cubic kilometers of material.

Now some of you will say something like “Hey dude, it never erupted continuously, so it can not be the same. And dude, the Siberian Traps erupted more material than Iceland”.

The reason for it not having erupted constantly is that it need either pressure enough to crack a continental plate, or the magma had to wait for a spot that was weakened that it could crack. The Siberian Trap was a momentous episode, but the largest separate eruption was “only” 3000 cubic kilometers of lava erupted (Norilsk Deposit). In the end the Siberian Traps is only standing for a slight elevation in erupted material even though a lot of magma had accumulated under the Eurasian plate before onset of eruption. Average erupted material during the Siberian Traps was only twice what Iceland is popping out on average.

The Siberian traps carved by a river into a kilometer high cliff.

We should also remember that eruptions happen in cycles. The Norilsk Deposit is probably a hundred million year event, or in other word, it would take on average 100 000 000 years in between every eruption of that size. It is estimated that it took about a hundred years to erupt that amount. So, on average 30 cubic kilometers per eruption year and that is not a nice thing to be around, but far from what it takes to produce a mass extinction.

We know that there are about 2 to 4 eruptions on the scale of above 10 cubic kilometers in Iceland today per every thousand years. They tend to happen on a 270 year cycle. We also know that every few thousand years we get them in the 30 to 50 cubic kilometers. Most likely those come in about 1000 year cycles, but in various places over Iceland, and on average over time.

About once every 10 000 years we get one upwards to a 100 cubic kilometers. I do not know of any eruption in Iceland significantly larger than that, and would be surprised if anyone finding one. The reason of course is that the MAR creates a fairly open passageway for the magma. Norilsk was happening due to the dense rock of the Eurasian plate storing up magma under it until it cracked, so the necessary magmatic pressure can most likely not build like that in Iceland.

So, now we know that old huge volcanoes cannot erupt again due to the magma-hose being disconnected as the plates slide away from the “gas-station”, and we also know how persistant the hotspot is.

Super volcanoes, well all is relative…

Bonus Riddle from Alan

Many of you might have missed that we tend to have volcanic and geologic riddles every friday in here. Lately we did not have that due to El Hierro taking center stage. But we do know that there are many that love them, so here is bonus riddle. Remember, it should end up in something rocky.

Huh! Last week, I went into a nice bakers – they only had this rock-cake!

CARL

What’s going on at Katla? Part III

Image from Wikimedia. Aerial picture of Katla.

Trying to make sense of complex phenomenae

In the first two instalments, we had a look at Katla as she appears through media and what she has done historically. It is now time to have a look at what’s going on and try to paint a coherent picture of what she actually is, is up to and able to do, but first let us recapitulate what we found previously:

• There is a general interest in Katla because she is and has been regarded as a very dangerous volcano by generations of Icelanders.
• The presentation of Katla in media is skewered by vested interests ranging from scientists who hope to increase their professional and/or public standing, people trying to cash in on the interest generated such as journalists and bloggers, and finally, there are people trying to increase their standing within the subculture of doomsaying and alarmism.
• Katla is a massive but relatively young volcano, located on the MAR, and formed when Iceland was covered by glaciers.
• The records include two large fissure eruptions on the NE flank of Katla; the prehistoric 5 km3 Hólmsá Fires of 5550 BC and ~22 km3 Eldgjá eruption in 934 AD. In historic times, the 1100 years or so that Iceland has been settled, there have been 27 listed eruptions (28 if the inferred minor subglacial 2011 eruption is included), 23 of which have been explosive.
• Of the 23 explosive eruptions, three have been assigned VEI 3, thirteen VEI 4 and four VEI 5.
• The four VEI 5 eruptions are remarkably alike in size at 1.2 – 1.5 km3, which is at the upper end of what Katla probably is able to do but at the very lower end of VEI 5 eruptions.
• Tephrochronology (in some cases complemented by radiocarbon dating) has identified a further 103 eruptions going back ~8,500 years, and in the few cases where a VEI has been assigned, none have been greater than a VEI 4.
• Katla does not possess a caldera-sized magma chamber.
• In order to account for the great number of explosive eruptions which involve more evolved magmas, Katla could have more than a single magma chamber.
• The available evidence suggests that in order to break through the up to 700 meters thick Mýrdalsjökull glacier, an eruption must be at least a substantial VEI 3.
• Direct and (primarily) indirect evidence suggests that smaller eruptions, mainly basaltic VEI 0 – 2 eruptions are severely underrepresented in her eruptive record and ought to exceed the number of observed eruptions.

Fig 1. Mýrdalsjökull showing the main glacier outlets, directions of jökulhlaups and areas affected. E –
Entajökull, S – Sólheimajökull, K – Kötlujökull, M – Markarfljot, Ss – Sólheimasandur, MS – Mýrdalssandur.
Eyjafjallajökull is to the left and the smaller glacier above is Tindfjallajökull (adapted from Google Maps).

The greatest danger from Katla comes from the very quick and extensive melting of the glacier caused by large eruptions which results in destructive jökulhlaups. There are three major outlets from the glacier: Entujökull to the NW that empties into the Markarfljot river and valley north of Eyjafjallajökull, Sólheimajökull to the SSW that empties onto the Sólheimasandur and finally, Kötlujökull to the SE that empties in a great arc east through south onto the Mýrdalssandur. What ought to be prime farmland and in fact once was settled, is nowadays an unsettled wasteland because of the devastating jökulhlaups unleashed by Katla. This is the true reason why Katla is considered to be such a dangerous volcano.

The fact that one often comes across the reference that in the days before the Hringvegur (ring road), “people were afraid to traverse the Sólheima- and Mýrdalssandur because of the frequent jökulhlaups” is another indication that smaller and unrecorded eruptions that cause only minor hlaups are far more frequent than the 40 – 80 years often given as the interval between main, and thus visible, eruptions.

Fig. 2. The foundations of the old bridge across the Múlakvísl river destroyed by the July 9th 2011 jökulhlaup
are visible to the left. The new bridge was laid down a week later. (photo John A Stevenson, GVP website)

Apart from the postulated connection between the Eyjafjallajökull and Katla volcanoes, one question that always crops up is the Goðabunga cryptodome. Many volcanologists maintain that it is a part of the volcanic system of the Katla central volcano. Others, notably Sturkell and his co-workers, claim it is part of the Eyjafjallajökull volcanic system. In order to shed some light on this issue, I asked our own GeoLurking if he could make a plot of all the earthquakes from 1994 up to and including the 2010 Eyjafjallajökull eruption. The results are quite clear and do throw up a surprise:

Fig 3. E-W cross section, view from south, through Eyjafjallajökull, Goðabunga and Katla. Plot by and
courtesy of GeoLurking. The “lines” formed at approximately 5, 3 and 1.1 km at Goðabunga and Katla are most
likely artefacts caused by quakes being assigned a poorly defined depth. The latter, 1.1 km, is the default depth
assigned by the automatic system in case it cannot compute a depth within the predetermined level of certainty and unless they are manually checked, which is not the case of every quake, automatic depth remains uncorrected, hence these artefacts.

From this cross section, it is quite clear that there is no connection between the Eyjafjallajökull volcanic system and Katla. Eyjafjallajökull has its own, well-defined feeder system from the Moho (first molten layer beneath the Earth’s solid crust) as does Katla, thus they are wholly independent of one another. As can also be seen, albeit not as clearly, Goðabunga too seems to be independent of either Eyjafjallajökull and Katla, the ramifications of which will be the subject of a later post by Carl. Sufficient to say that when we contemplate what Katla herself may be up to, we must differentiate between activity at Goðabunga and activity at Katla. Once we do, we see that while Goðabunga is more or less continuously active, Katla operates in bursts and seems to be most active during summer and autumn when the ice cap is at its, relatively speaking of an up to 700 m thick glacier, thinnest.

Fig 4. Activity post-Eyjafjallajökull. Activity at Eyjafjallajökull is minor and has to do with the system settling down after the end of the eruptive phase. Note that at a depth of 0 to 5 km or so, there seem to be three separate areas of activity at Katla. (Plot by and courtesy of GeoLurking.)

After the Eyjafjallajökull eruption, Katla seems to have entered an active phase with a suspected subglacial eruption on July 9th 2011 and several pits or craters forming on top of the glacier. This activity seems to be localised to three main areas within the caldera:

Fig. 5. Earthquake activity at Katla July 9th 2011, the day of the jökulhlaup and suspected subglacial eruption. Both the 1823 and 1918 eruptions occurred close to but just east of this area. The 1823 eruption occurred close to the easternmost red spot while the 1918 eruption was roughly at the rightmost dark blue spot below it. (IMO)

Fig 6. Earthquake activity at Katla July 17th 2011. (IMO)

Fig. 7. Earthquake activity at Katla July 21st 2011. The 1755 eruption was situated in the same area as the three overlapping orange spots. (IMO)

As can be seen, there are at least three distinct areas of activity inside the caldera with the one associated with the inferred July 9th eruption well to the south. The pits formed in the glacier also align with these three areas, albeit the pits to the northeast seem more drawn out along the caldera wall and not over the center of activity. These three areas seem to tie in with the three areas of activity noted in fig 4 as do the locations of three of Katla’s major eruptions. Thus there is not a single vent, but at least three at surface distances of approximately 5 to 8 km from each other. It is equally likely to judge from Fig 3. and Fig 4. in conjunction, that at great depth, they do have a common source.

I will now present you with my personal view of Katla, but do not be afraid to disagree or draw your own conclusions (within reason please, no Katlatubos here):

Katla is a young volcano and far more active than has previously been thought. Unlike the similarly aged but much less active Eyjafjallajökull, Katla has had more time to develop her system of sills to the point where they are fewer in number than they originally were but have a substantially larger magma-carrying capacity and approach or may have reached the point where they can be considered magma chambers proper. Since cooking evolved magmas takes a long time, usually millennia in the case of cubic kilometre-sized silica-rich magmas and at the very least many centuries for intermediate magmas, it is highly likely that Katla possesses several pockets of magma capable of eruptions ranging from high VEI 3s to small VEI 5s. Not only do the times between such eruptions argue this, their wide spread of location within the caldera does so too.

The most common type of eruption at Katla is the small, subglacial eruption of a few tens of millions of cubic meters of basaltic magmas. These eruptions are not energetic enough to break through the very thick Mýrdalsjökull glacier and the only proofs of their existence are intense earthquake swarms followed by minor jökulhlaups and later observations of deep pits or craters, sometimes water-filled, in the glacier ice. My guesstimate is that there may be many such small eruptions over any given ten-year period, and possibly in the case of a period of high activity, there may even be more than one in a single year. By back-tracking and investigating old accounts over the past few centuries of jökulhlaups in the area not associated with visible eruptions, it ought to be possible to identify many of these minor eruptions.

While a larger “proper” eruption of Katla in the VEI 3 – 5 range cannot be ruled out, I find one unlikely at present as the current activity mostly is in areas already depleted of evolved magmas by geologically speaking very recent major eruptions. Also there is little sign of the uplift required on GPS. If one were to occur, the odds for one towards the upper end of what Katla is able of ought to be better in the Eastern to Northern parts of the caldera.

Finally, what we do see when we look at SIL-stations such as Austmannsbunga, located on the NE caldera rim (not a coincidence, see above), is hydrothermal activity following a period of possibly still ongoing magmatic intrusion and not signs of an imminent, large eruption.

Fig 8. Hydrothermal activity at Katla as shown on the Austmannsbunga SIL (IMO)

I’m sorry to be such a boring old fart, but if this is unsatisfactory, start looking for intense earthquake activity at some 25 – 10 km depth, showing on the IMO map for Mýrdalsjökull as being in the Eastern to Northern part of the caldera, activity that shows a clear upwards trend and spreads when it reaches depths approaching 5 km!

HENRIK

Herðubreið – Renewed activity at Askja

Photograph by Zanthia. On the picture one can see Mount Herðubreið. Herðubreið (Broad Sholder) is a tabletop mountain, or in another word, a Thuya.

Yesterday an earthquake swarm started with a 3.4M earthquake at Herðubreið. So far the swarm has had 15 earthquakes above 2M, among those 3 where at Askja proper. This swarm as well as the previous ones at Herðubreið have been to the west of the volcano. And those earthquake swarms have been deemed to be lateral intrusions from Askja.

Image by Icelandic Met Office (IMO). Askja to the left of the green star, the black “circle” above is Frémrinamúr. Kverkfjöll is due south and not showing here.

Image by Icelandic Met Office (IMO).

Only problem here is the 3 earthquakes that happened within Dyngjufjöll (Askja). Having 3 earthquakes above 2M at the same time as a medium sized earthquake swarm takes place rather beggers coincidence. I think when the hubbub of this is over the area will be removed from Kverkfjölls fissure swarm. One should also remember that Kverkfjöll is the smallest volcano on the riftline.

Image by Icelandic Met Office (IMO). There seems to be magmatic components to the earthquake swarm when looking at a higher resolution.

On the other hand, this is as far as known not anywhere near any part of Askjas fissure system. We should remember that. Personally I thought up untill now that Herðubreið itself belonged to the Frémrinamúr volcanic fissure swarm. Apparantly I was as wrong about that as the ones who thought it belonged to Kverkfjöll.

Image by Icelandic Met Office (IMO). The earthquake swarm shows well also at the Dyngjufjöll SIL-station.

So, now we are back to a long dormant volcano that had it’s last eruption before deglaciation. And that put it as having erupted at 6000BC latest (time when the glacier withdrew). How do we know that? Thuyas only form under glaciers that are big enough to contain the erupted lava thusly forming the tell-tale tabletop look of a thuya. So, we are talking about a long dormant volcano here.

Image by University of Iceland and Professor Sigrún Hréinsdottir. Inflation showing at Askja. The inflation at Herðubreið started 2 years before.

If we look at the 12 +2M earthquakes we find that 9 of those are between 2.2 and 7.9 kilometres deep. 2 of them are 1.1km deep, and that is a dummy value when an actuall depth has not been set, then we have the original 3.4M quake that has a suspiciously undeep figure. The current given depth is almost certainly around 5 to 7km and will be revised sooner or later. What does this then tell us? That the figures point towards a magmatic intrusion into an old chamber. Remember, this is my interpretation.

So, back to Herðubreið. What is Herðubreið? In my eyes Herðubreið is starting to look like a volcano on it’s own. One of the reasons is that it started to inflate just to the east before Askja started to inflate. It in fact started inflating and having earthquake swarms to the east before Askja stoped deflating. So, I am actually contemplating that Herðubreið and Askja had a common origin and has been rifted apart by the EISZ part of the MAR over the course of millenia. What I am trying to say is that they might actually share a deep root found in the current EISZ. We could think of them as two non-twins sharing the same womb and umbilical cord.

Untill we have new data from the area this is a bit speculative, but I do not think it is that much way off.

CARL

Tungnafellsjökull – Tectonic Earthquakes

Photograph by our own Jamie. Tungnafellsjökull seen from Sprengisandur area. Notice that the Jökull is almost gone from Tungnafellsjökull, soon to become known as Tungnafjöll only.

There has been an earthquake swarm at the northern end of the Tungnafellsjökull during the evening and throughout the night. The swarm is still ongoing. There has been a lot of speculation out there in the blogosphere about it being volcanic in nature. It is not, it is purely tectonic.

As some of you know Iceland is divided by the Mid Atlantic Rift (MAR). The MAR in turn is divided in Iceland into two separate active seismic zones, the Eastern and the Western Icelandic Seismic Zone. Lately it has been the EISZ that has been most active of the two. But the WISZ is not in any way dead or dormant. Both of them are driven by the spreading of the MAR. From the WISZ the North American Plate is spread, and from the EISZ the Eurasian Plate is spread. In between them are two micro-plates that have formed by volcanism caused by the rifting.

The map is showing the Icelandic Volcanic Zones, where the MAR runs up into Iceland, where the MAR leaves Iceland and the more important volcanic features. The Icelandic Seismic Zones are corresponding to the volcanic zone.

Along both the WISZ and EISZ are lines of volcanoes spread, it is where the spreading causes magma to pour up and fill the spaces created by the spreading.

If you look at the map you see that WISZ runs from Hengill, up to Langjökull (2 known volcanoes), via Hofsjökull (at least one volcano), onwards through Tungnafellsjökull, and then ending up at the triple-junction at Bárdarbunga.

During the last few years the area of Tungnafellsjökull has been inactive, but there is ample evidence of it having been tectonically active, something that can be found in the Sprungur (tectonic faults) found in the area. The dormancy is likely due to the area having been locked at depth, probably by old magma that has solidified the area.

Various versions of tectonic faulting. Tungnafellsjökull is suffering from strike-slip faulting.

Lately the area has been subject to an uplift not seen in Iceland since de-glaciation after the last Ice age. This is due to the melting and diminishing of the glaciers of Tungnafellsjökull (almost gone) and Vatnajökull. This uplift process has accelerated during the last decade. It is now up to 3 cm year in the area according to Sigrún Hreinsdottir (source, private email). Yes, the famed inflation of Hamarinn is not happening, it is a combination of Grimsvötn motion and isostatic rebound.

This motion might have started to release the seismic lock at Tungnafellsjökull. If that is so, there is a risk that the swarm of earthquakes is just precursor quakes for a large earthquake.

This map shows the features discussed in this text in relation to the Bárdarbunga triple-junction and the hotspots location.

What makes this interpretation the more likely one is that there is no discernible evidence of any harmonic tremoring during the earthquakes. This makes it into tectonic seismicity, not magmatic seismicity.

If there would be a large earthquake that tears the rift-lock, then magmatic movements could start in the area, but not before that. Worst case scenario here is not a volcanic eruption; it is a 6M earthquake as the slip-lock disintegrates over a large area.

Another thing that I want to point out, the earthquakes are all of low probability and some of them are as I write this due to change after revision, and some of them will be removed due to being false representations of earthquakes, so called Ghosts. And as I wrote this IMO has started to revision the earthquakes, right now there is at least one at 3M.

CARL