Magmatic intrusion at Greip

Vatnajokull: what lies beneath. (Radar image taken by the Sentinel-1, 4 Nov 2019)

As some has noted there has been quite a bit of activity in the last week at a volcanic feature that we have chosen to call Greip located north of Grimsvötn. We have previously written quite a bit about this feature and even gone so far as to state that it might be in a pre-volcanic state.

To recapitulate briefly what we know so far about Greip we first have to look at if there is something looking like a volcano on top of the point of interest, and we know that there is no edifice at the location. So, it has not erupted yet.

That being said, it was associated with the Holuhraun event in as much that the propagating dyke turned sharply to the north as it approached the northwest quadrant of Greip. At the least this means that the systematic pressure was to great for the dyke to proceed in that direction, some do though believe that Greip might have aided in the magma supply chain for the eruption.

Why do we think it is a proto volcano? This might be the simplest question to answer. Greip has since 2012 suffered from deep earthquakes indicating magmatic ascent into the system from depth. This activity has been incredibly persistent and narrowly defined into a clear deep feeder tube.

From 2012 onwards these earthquakes have slowly increased in numbers, and also moved on upwards from depths of around 35 kilometres to the current earthquakes between 20 and 12 kilometres. At the same time the general size of the earthquakes has increased about 20 percent, this might though be due to the magma pushing apart less hot and more brittle material causing more defined earthquakes.

In my last article I wrote that the magma slowly intruding under Greip had started to manifest itself as minor trackable movements in the GPS-trajectories, something that continued ever so slowly and minutely until last week.

 

A brief Bárðarbunga digression

During Holuhraun II eruption in 2014 we found that Bárðarbunga was not a triple-junction volcano as previously believed, instead it turned out that it is what might be the only meta-stable quad-junction volcano in existence.

From Langjökull running towards east via Hofsjökull and Vonarskarð you have the Mid Icelandic Belt, a volcanic rift zone that enters into Bárðarbunga from the west, Bárðarbunga itself is located on the western side of the East Volcanic Zone that is running in an SSW to NNE angle through Vatnajökull. This made Bárðarbunga into a triple-junction volcano.

But, as the Holuhraun II event started in 2014 we saw a clear path going towards east deeper into the East Volcanic Zone. We also know that this feature has been active at least once before, during Holuhraun I eruption in 1797 (this eruption was previously attributed to Askja).

Quad-junctions are inherently unstable and normally collapse into 2 different triple-junctions, this has not yet happened, so for the time being Bárðarbunga is a meta-stable quad-junction. The collapse will probably be caused by the Mid Icelandic Belt becoming defunct in the next 100 000 years or so.

What on earth did this now have to do with poor young orphaned Greip? Well, it makes it a triple-junction on the wrong end of Bárðarbunga since it is also sitting on what probably is the northern tip of the Grimsvötn Fissure Swarm. In other words, Greip has some violent parents.


 

The Week of the Living Greip

So, what then is the reason that we once more venture out into yet another article about a volcanic feature in Iceland that is not erupting when there are so many interesting volcanoes around the planet?

Well, as it turns out I have spent a few weeks reading up on and writing on an article about Monty Pythons favourite volcano, Kilimanjaro. In other words, not even I found Greip that interesting at the moment.

And like for all neglected puppies and babies throughout history there are two golden rules. One, if they are quiet you should assume that they are up to something bad. And, when you least expect it, they will manifest something really bad if you neglect them.

Puppies will chew up your handmade Italian shoes, and babies will inevitably find a crayon and redo your living-room walls into the Sistine Chapel. Volcanoes on the other hand will intrude glorious amounts of magma if you do not give them enough attention.

All alone under the ice Greip has suffered from six separate intrusive events in the last week. One can see them as smatterings of deep earthquakes ranging between 22- and 12-kilometres depth, but what is not seen is the extended periods of tremor that is accompanying those earthquakes.

The longest of those tremor periods lasted for slightly less than 4 hours, indicating that during the time frame there was freely flowing volcanic fluids. And at that depth it is not geothermal waters.

All of the earthquakes have been clearly defined inside the area that we have named Greip, so we know that it is not caused by any outside influence.

The Bardarbunga-Grimsvotn area in radar. Close-in of the image at the top

 

Greip and the GPS

Last time I wrote about Greip I explained how hard it was to separate Greip related signals from the other volcanoes in the area, but that it was possible and that there indeed had been inflation at depth.

This time around there is no need for careful data-analysis to see how Greip is affecting the general area, not when it is kicking stations about like it was playing football (not the American soft-rugby version).

GFUM (Grimsvötn) has been kicked 20mm south and 35mm up during the week. KISA (Bárðarbunga) moved slightly to the North-East and Up. The other nearby stations have also been moved around a bit while going up.

The sharp up-component will probably be temporary as the fissure swarm that Greip is situated on adjusts, so the trend should go down a bit, or at least slow down.

Kisa

 

Greip and the future

Seeing a young volcano prior to its first eruption is in many ways a dream to research, because we have never seen how a volcano works as it is born. All we have are theories, and now finally we get to match them against real world instrumental data.

There is obviously quite a large risk that in the end Greip will fizzle out and never erupt, but it is allowed to hope for good things to come.

Currently there are four possible futures as I see it, five if you count the fizzle out possibility (but let us stay positive).

The first possibility is that as magma intrude, we will start to see more intense swarms as it gradually moves upwards due to heat-buoyancy, and that in a few years or decades our new little baby volcano will be born, wrinkled face and all.

If since it has done 23 kilometres in 7 years, I would say that it could erupt in about 5 years’ time at the going rate.

The second possibility is that Greip was helping out feeding the Holuhraun eruption. That means that it is quite possible that it might push magma northwards through the dyke towards Holuhraun, and that it will erupt there.

In my opinion this is not that likely since there is no remaining strain to rip apart a dyke in that direction.

The third option is that the magma will enter into the part of the dyke that is going between Greip and Bárðarbunga. This is not entirely impossible since Bárðarbunga is still under fairly low-pressure after the eruption in 2014.

Having hot deep gas-rich magma pushed backwards up through the wazoo of Bárðarbunga would probably become interesting. It would likely cause a fairly substantial caldera-eruption.

So far nothing seems to indicate that this is happening. There are no earthquakes in that part of the dyke, and Bárðarbunga is about as demure as it can be with its occasional Mw3s.

The fourth option is that the magma starts to move at depth along the Grimsvötn Fissure Swarm towards south feeding into the northern magma chamber of Grimsvötn. As of now we have not seen any substantial number of earthquakes indicating a rapid increase in magma influx into this volcano, so for now we can count this one out.

That being said, if magma started to move towards Grimsvötn we would rapidly see an eruption.

Whichever of the options that will manifest itself I am certain that we will start to see more vigorous and shallow earthquake swarms in anything from hours to a few months.

CARL REHNBERG

48 thoughts on “Magmatic intrusion at Greip

  1. Interesting. The very last bit caught my attention: “Whichever of the options that will manifest itself I am certain that we will start to see more vigorous and shallow earthquake swarms in anything from hours to a few months.” That’s quite a bold statement and if it’s correct we are heading towards very interesting times.

  2. Little question on the Sentinel picture: is that heat I’m looking at? White being the hottest? Or is this something else entirely?

    • The radar shows the brightness of the backscatter. It is essentially the texture of the surface. Smooth surfaces are less bright in radar. The Bardarbunga crater shows up well but I am not sure why! Grimsvotn gives the impression of a 10-km wide crater, not much smaller than Bardarbunga. Note in the top image that Holuhraun shows up very well, and not the dark-blue crater lake of Askja. At sea, wave height can show up.

  3. Fascinating. Thank you for the news about Greip! I was a little sad my suggested name for this oncoming edifice (Olnbogimótumeldfjall) never became popular. Greip is too easy for journalists!

  4. This would be the first icelandic eruption I would have monitored from beginning to end, (This is actually Tallis now) I do wonder if it would explosive or effusive

    • Explosive first when it goes through the Glacier
      Pheratomagmatic surtseyan subglacial.

      If it lasts long enough it may become effusive.

      Maybe Greip will become the next Gjalp eruption again?
      Greips first eruption become like Gjalp?

  5. If Grims goes off in the next year or so (as has been predicted) how will that affect baby Greip?

      • At this depth, magma still can fin a way around. Bardarbunga and Grimsvotn should be within reach. However, it would not directly feed eruptions at that location. It would inject new magma into a local magma chamber.

        • Greips magma is probaly the same very hot basalt magma that lurks inside Bardarbunga and Grimsvötn.
          Infact Greip maybe situated closer to the Iceland Hotspot centre than either Grimsvötn or Bardarbunga

      • @GeoLurking – this is something I wonder for I while now. What speaks for Greip being a volcano in its own sense and what against it being a chamber of Grims? In the end it is the continuation of the Grimsvotn fissure swarm. (Does the Grims fissure swarm continue north of Vatnajokull?)

        • The greatest evidence is the apparent chamber shape to it. I can’t really conclude that it isn’t part of Grimsvotn. Chambers in this area seem to be a series of stacked sills.

  6. Interesting times ahead.. If Greip decide send some hot magma down the line to Grims. What scenario are most likely.? Central volcano eruption or can it wake up old fissure.. Probleby i am “out bicycle” as we say in sweden when we totaly wrong.. But thinking about Laki event and how much it produce. Maybe a extra sourse are what’s needed.. What ever happends its can soon be time for a “Greip Tonic” and follow the show.

  7. My good friend Carl Rehnberg, you forgot about option 5 and option 6:

    Option 5: Magma follows the dike between Greip and Bardarbunga and then follows southwards towards the Veidivotn fissure swarm. There is enough strain for this to happen.

    In my opinion, the magma will most likely flow into Bardarbunga caldera and from there, no one knows what is more likely. Why do I say this? Because prior to Holuhraun, magma first flowed from Kistufell into Bardarbunga and from there into Greip and Holuhraun. So, the dike into Bardarbunga is probably still hot and the pressure at Bardarbunga even lowered than back then.

    It might actually be doing that since a long time, and we cannot see it because the region is still very hot, so any earthquakes will only be visible at the Bardarbunga caldera.

    Option 6: Magma does the same thing but flows from Greip into Bardarbunga and then into Hamarinn and erupts there. This is assuming such a connection.

    In my opinion, the three most likely scenarios are:
    1) Magma simply flows into Bardarbunga caldera, and triggers a strong eruption there.
    2) Magma flows further, towards the Veidivotn region, and triggers a flood basalt event
    3) Magma flows into Grimsvotn and triggers an eruption there.
    4) Magma flows into Hamarinn and triggers an eruption there.

    With the option 5, we might be for a patient wait, as probably the level of pressure required to erupt at Veidivotn is pretty big…

    Because magma has been flowing so much between and into these different volcanic systems, I think its mostly fresh basalt, so I do not foresee any violent eruption (no mixing of evolved magma with fresh basalt), but instead more eruptions of a large volume of basalt. Like the ones in 2011 and 2014.

  8. Most of the action still takes place around 17 to 20 km depth.
    Could the ‘boat hull’s keel’ be the cause of it?

    The rifting pulls and possibly is unzipping new path, extending the hull’s body very slow to NNE.
    Last months it seems to me that in the swarms taking place, a ssw nne pattern is present.

    Btw Kista gps has a strange behaviour, quite different than other stations at or near Vatnajökull, it went up a lot and the rapid movement over the years, the longterm graph version, hasn’t been explained properly as far as I know. Wouldn’t be surprised if other geological processes than inflation and rifting are involved here aswell.

        • It seems dirty on the lens. The thing does not change its position at all. If it would be emission it would swing to the right and left side, with the change of wind…

        • It depends on how bright the sky is behind it. You see it when it is brighter, and not when it is darker. Obviously you won’t see it when the sky behind is the same tint as the dirt.

  9. In order to understand what might happen at Greip, can someone freshen my memory and remind me the mechanism of the Holuhraun eruption?

    1) First thing: was the Holuhraun eruption caused by one large magmatic intrusion that triggered the rifting, or was it caused first by the cumulative tectonic rifting tension which eventually gave away into a large section of Iceland ripping apart and this allowed the result of successive intruded magma to finally erupt? Which one was it?
    2) The magma erupted at Holuhraun followed and correlated closely with the collapse of the magma chamber at Bardarbunga. Why this connection and what stopped it? Was it simply when an equilibrium in magma pressure was reached within the entire chamber and dike?
    3) Did further rifting (plate movement) happened after the eruption stopped and magma plugged the dike? If that continued to happen, then magma has continued to intrude and fill the dike space…

    • 1. Bardarbunga is not on the rift. It may have been when it formed but over time it drifted away, together with the plate it is on. Over half a million years it would have drifted by 10 km. So no, it wasn’t caused by rifting. However, when the dike that it created hit the rift, it turned 90 degrees and started following that, making use of the low stress.

      2. It was the same magma. It is not just the volume that shows that, and the good correlation between the subsidence of one and eruption of the other, but also the fact that the pressure in Bardarbunga (declining as an exponential) determined the eruption rate. As the pressure got less, the eruption declined. The eruption ended when the pressure become so low that the magma took longer to travel through the dike than it took to solidify on route. That is why it stopped rather suddenly.

      3 I think not. The subsidence ended the moment the eruption did.

  10. Again several deep earthquakes unter Vatnajökull… this time located more in the western part. Another indication that magma is on the move. Option 3 or 4 of Carl or 1 and 4 of Irpsit can not be ruled out at this time.

    The reactivation of the Veidivötn fissure on the long run is also a possibility, especially when we take the recent earthquake activity In the Torfajökull area into account.

    • Still ongoing…Askja isn’t a happy lady it would seem!

      (First comment on this site from a long-time lurker – love the work everyone puts in here to help me spend many evenings nerding out over Iceland!)

      You are welcome! First comments are held for approval and can take a few hours to appear. Future comments should appear immediately. – admin

        • My impression too. If related to pressure from Askja, it could induce movement on a fault. Or it could be movement on the rift. The stretch between Holuhraun and Krafla has escaped attention: few earthquakes and no easy access to magma.

        • And the swarm is away from the caldera ring faults where an intrusion would be expected to first rise through. It could be tectonic or as you say a nearby fault activated due to increased pressure of the magma chamber.

  11. An ongoing long sqarm at Askja. if the swarm gets suddently large, I wouldn’t be surprised by seeing a fissural eruption in the east of Askja.

    Magma could have reached there after Hoiluhraun ans Askja was expericing intrusions since several years.
    Its the easiest exit for magma in the region, other than Holuhraun, with an eruption there last in the 1960s.

    • It is on schedule – volcanoes always are. Just not our schedule. It actually follows the predicted curve very closely.

      • The increase in Geothermal heat and melting of the glacier in Grimsvötn
        Coud be signs that the conduits are more open now?
        Grimsvötns ice shelf on its lake is melting now.

        • Increased heat flow can mean that magma is closer to the surface, or it can mean that water circulates more easily between the hot deep layers and the surface. I don’t know, though, whether it is unusual for the lake to have open water.

    • Yes, we likely have to wait some time more …. 🙂
      Looking at the graph we haven’t entered the up running phase where thing speed up, which I marked with dotted lines. We haven’t got thet steep yet.

      Maybe we should start counting from the day that Bardarbunga’s chamber stopped emtying via the Holuhraun eruption (marked with H’s end).

      Some cut and paste action from my computer..
      When we take that day as day 1, the schedule is about right indeed. The two larger quakes in the cumulation takes us a bit advantage.
      One to two years ahead?

      • The emptying of B’s chamber could have frustrated the pressure building in Grims.

        that in reply of Jespers … and sorry for the typo’s.

  12. In the last 18 hrs or so, Mauna Loa’s experiencing a swarm of very shallow/surface shocks inside the caldera, with another shallow cluster in the SW rift zone. So far, drumplots are not showing any magmatic signatures but rather what looks like rock-fracturing events. This sequence appears to be quite a bit more robust than recent flurries. Deformation data at the summit is also showing a minor but noticeable increase in the last 24hrs., both vertically and horizontally at MOK.
    Not sure if an eruption is imminent……most likely not, given the absence of tremor….but given the rather sudden spurt of shallow hypocenters (most shocks in last few weeks were around 3km deep), at the least there does appear to be a sudden pressure increase going on directly under the caldera. Staying tuned.

Leave a Reply