Bárðarbunga – Nature of the beast

Dyngjujökull. Photograph by Eggert Norddahl. Used by explicit permission. If you wish to use the image contact Volcanocafé via our email.

First let me write one thing, and that is that we are not in Kansas anymore. And with that I mean that we are in totally uncharted country. Icelandic Met Office has the best volcanologists on the planet, and they pretty much never make a mistake. They are quite simply the best and their reputation at this site is set in solidified lava.

So, when people like that in an hour first states that a small eruption has started and an hour later recant on the statement it does not hamper our confidence in their abilities, it is instead a sign of how “out there” what we are seeing right now really is.

What is happening now is really like if you walked down a familiar street and turn a corner and find yourself in the fabled Land of Oz

So it is time to sit down and calmly go through what is happening, and what has happened previously. Of course this will just skim the surface, but hopefully it will be enlightening.

In the beginning

Bardarbunga. Dyngjujökull. Photograph by Eggert Norddahl. Used by explicit permission. If you wish to use the image contact Volcanocafé via our email.

There is of course not any beginning to our story, instead this story has been ongoing for 14 million years, and what we are seeing now is just a single word in the entire story of Iceland’s birth and growth.

So, let us just say that Bárðarbunga is the largest volcano of its type on the planet, and that it has had the largest lava flood eruptions in the last 10 000 years, and that it is prone to have what is called rifting fissure eruptions.

A rifting fissure eruption is when a large part of the fissure swarm “rifts”. Rifting is when a large part of a fissure on Iceland opens up all the way down to the mantle and as that happens a large scale decompression melt starts in the mantle and obscene amounts of magma is formed and pushed upwards filling the void that is created as the tectonic plates move apart.

Bárðarbunga has had more than half of the Icelandic rifting fissure eruptions, and of course the largest. Last time that happened to Bárðarbunga was in 1477 when a fissure opened up at Veidðivötn that extended all the way down to Torfajökull (causing an eruption there) and it also caused a VEI-6 caldera event at Bárðarbunga central volcano. The next time it happened was at the 1783 Skaftár Fires (Lakí) that happened on the Grimsvötn fissure swarm.

Back in 2010 Icelandic Met Office issued a statement that a phase of increased volcanic unrest was to be expected. These phases are due to Icelandic volcanism being cyclical, and there are two cycles. One is the Icelandic Mantleplume activity cycle; the other is the Icelandic MAR rift cycle. This time around both cycles would coincide.

Back then I also hypothesized that the rapid melt of Vatnajökull glacier would increase it further due to isostatic rebound (land lifting due to weight on top disappearing) would cause increased decompression melt.

Bárdarbunga. Dyngjujökull. Photograph by Eggert Norddahl. Used by explicit permission. If you wish to use the image contact Volcanocafé via our email.

All of this made me start to look for signs of unrest in the southern parts of the fissure swarms, and about two years ago I saw an uptick in earthquake activity at both Skaftár fissures and at Veidðivötn fissure swarm. Problem is just that there is extremely little scientific work done about these, the largest eruptions of their type on Earth. Basically there is only one good paper out there. This led me to do my own research and write a series of articles in here about the Skaftár Fires. I seriously suggest everyone to read those to get a better picture of what is happening now. My own research gave results at odds with what was previously believed about large rifting fissure eruptions, but it was based on enough data to make me believe in the validity of the result.

Around this time I and GeoLurking started to look sternly at what was going on in Iceland, and especially to track earthquakes in odd spots related to the fissure swarms.

Slightly more than a year ago odd small swarms started to appear in the area we are now looking at, and I concentrated on those that happened on the Bárðarbunga fissure swarm. Chiefly among those I noticed small swarms of deep earthquakes (20km+) under Kistufell and Trölladyngja. At the same time I noticed two odd swarms at equal or even greater depth at two points out in nowhere land. I thought those two swarms was just some odd volcanic activity related to unknown small volcanoes. Interesting, but not what I was on the prowl for.

As the months turned into a year of constant and slowly increasing activity I felt pretty sure that something was going on, and that it was time to write about what I thought would be an upcoming eruption on the Bárðarbunga fissure swarm. I though delayed writing the article for two weeks while debating it with a couple of the editors in here. In the end I decided that it was time to write about the upcoming event.

As things go I must have looked like a blatant psychic, the swarm started just a few hours later. Obviously most tree stumps are more psychic than me; instead I used science at every corner. I am though happy to have been the first to spot what would come.

What I find interesting is that those two deep swarms out in nowhere land are exactly at the spots where the meandering intrusion changed directions. That is just a bit too much of a coincidence, so I now think that those where signals of what would be coming, just that we missed them.

Now, let us look at the present.

Seismicity

Image from Icelandic Met Office. Corrected earthquake seismicity plot from onset of the swarm showing the collapsing caldera and the propagating intrusion.

Let me first start with the seismicity, in my Skaftár Fires series I wrote that we would be seeing almost constant M4 and M5+ earthquakes in an upcoming larger event in one of the fissure swarms, right now we are seeing exactly that. I do suspect we will see more of that later on if the fissure actually starts to rift. There are no signs of the seismic activity abating now, I would expect it to continue or even increase.

What is interesting is that at the current direction and speed of propagation the swarm will reach Askja in 4 days.

GPS orbits

Image by Icelandic Met Office. Kverkfjöll GPS Genggisig (GSIG).

 

Image by Icelandic Met Office. Dyngjuháls GPS-station (DYNC).

Dyngjuháls (DYNC) has changed its orbit slightly and the rapid north motion has shifted to a slow south motion as the intrusion has passed the GPS-station. The westwards motion goes on unabated and the station has now moved 185mm in that direction.

If we look at the Kverkfjöll station named Gengissig (GSIG) we see 90mm of southwards motion combined with 180mm of eastwards motion.

If we now combine the west motion of DYNC with the east motion of GSIG we get a total rifting of 365mm in 8 days. That is an average of 45mm per day, or the equivalent motion of 14 years of normal Icelandic rifting done in only 8 days.

These two stations are though a bit distant from the rifting fissure, so the rifting is obviously larger than that. Most likely the rifting right on top of the dyke is in the order of a meter or more. This means that more than 0.8 cubic kilometers of magma has intruded.

Now, even that number is on the low side since the “lips” of the rifting fissure are still closed. As the lips open the total rifting will most likely be closer to ten or twenty meters if it occurred now. And the longer the intrusion continues before onset of eruption the larger the fissure opening will be.

Other signs

Except for this there are so far no other signs of volcanic activity. There is no gas measurements (if they are taken) indicating an eruption being close, neither are there gas or particles in the glacial run off indicating melting ice from an eruption.

Now, let us move on and talk about what type of an eruption will be most likely at this juncture in time. Remember that this might change as things evolve further.

1. The seismic activity decreases and the intrusion lose momentum and no eruption happens at this time. For every day this scenario becomes less likely. In the beginning most scientists stated that it was fifty/fifty that an eruption would happen. The chance of it not happening is now probably below ten percent chance.
2. A small sized eruption at Bárðarbunga central volcano. This is now a very unlikely scenario since the pressure is decreasing inside the caldera.
3. A large phreatic event in the caldera due to magma chamber collapse. This is an increasing risk as the roof of the magma chamber is currently lowering causing those large earthquakes noted in the caldera.
4. A small scale fissure eruption like the 1996 Gjálp. The risk for this has significantly decreased as things have moved on.
5. A medium sized prolonged rift episode like the Krafla Fires. This is currently the most likely scenario.
6. A large rifting fissure eruption. As time goes by the risk for this increases, currently I think the risk is around 10 percent. So, I guess it is time we start talking about this in the open and what it might entail. I once again recommend reading my series about the Skaftár Fires.

Rifting fissure eruption

Dyngjujökull. Photograph by Eggert Norddahl. Used by explicit permission. If you wish to use the image contact Volcanocafé via our email.

Let me be clear about what this is, it is about as large as an eruption is likely to be in this geological era. Only full scale trap formations and supereruptions are larger.

But let me start with why I think this is an option. Foremost the length of the fissure, at 40km it is definitely long enough to be able to sustain a large eruption. The fissure is also showing signs of having opened up down to the mantle at places, and that would mean that it is possible for rapid decompression melt to occur, and that is a necessity for a large rifting fissure eruption to access large enough quantities of magma.

The most surprising sign though is that this rifting fissure is not following a single fissure swarm. This is totally unsuspected behavior that nobody has even guessed at in their most feverish fantasies. The initial intrusion charged straight out of the Bárðarbunga fissure swam, passed barren land in between fissure swarms and connected with the Grimsvötn northern fissure swarm, followed that downstream and then once again changed trajectory and entered the fissure swarm of Askja.

This means that potentially the intrusion might be feeding on the 3 largest Icelandic volcanoes if the fissure evolves a bit more. If this actually happens all bets are off and we would be most likely talking about a rifting fissure eruption with explosive components.

If the intrusion continues to move forward in this direction it will enter the caldera of Askja in 4 days. Problem here is that Askja is known to have pockets of rhyolitic explosive magma, and if those pockets suddenly reheat from the new hot magma things could get interesting fast.

Commenter Irpsit has pointed out that the area seems to be more prone to form single stage eruption volcanic shields instead of rifting fissure eruptions. I think this has great merit on what we are seeing, and that it is the single most likely thing. It is though not necessarily a better option since it would entail years and many cubic kilometers of highly gas rich magma coming forth at rapid pace.

Above I have touched on the worst case scenario. If that happens we will face temperature changes, ash and voluminous gas clouds. But one thing is certain, it would not in any way threaten life on earth, it would not even put a big hindrance on your daily life. Get real, the world will not end like this. But, expect a bit of nuisance.

CARL

Prequel to the Skaftár Fires series – https://volcanocafe.wordpress.com/2013/05/29/central-volcanoes-of-vatnajokull/

Part one of the Skaftár Fires series – https://volcanocafe.wordpress.com/2013/06/05/laki-deconstructed-anatomy-of-an-eruption/

Part two of the Skaftár Fires series – https://volcanocafe.wordpress.com/2013/06/10/laki-deconstructed-grimsvotn-and-beyond/

Part three of the Skaftár Fires series – https://volcanocafe.wordpress.com/2013/07/31/laki-deconstructed-a-timeline-for-destruction/

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