Posted on by Jón Frímann

Grímsfjall continues to inflate

I see that many people think that Grímsfjall has started to deflate due to a drop in GPS measurements. But the “Up” part of the GPS measurements have been dropping over the past few days from about 85mm and down to about 65mm today.

As that may be true that the mountain has started to deflate from the top. It is not to say that deflation process has started at Grímsfjall. As the GPS data clearly shows that a inflation process has just moved from the top and to the south. But current GPS measurement clearly show that Grímsfjall is now inflating to the south (15mm today) with minor inflation to the east (about 15mm today). So it is clear that the magma is moving inside the volcano from one location to a other over the past few days. What that means is unclear at the moment. But it appears that the inflation to the south is speeding up at current time. This might get interesting soon in my opinion. Regardless if there is a eruption or not.

Data: ISGPS GFUM
Vatnajökull continued GPS data project from 2004.

25 Replies to “Grímsfjall continues to inflate”

  1. Jón: As I said before, I see it in a very layman way: it is a mass of semi-fluid material, unable to push upwards against gravity, which happened to find an easier way (some fissure or crack) to flow away from its underneath source of pressure. Whether it will have enough strength to come airborne, it is another question. Maybe it will just “fill in the blanks” and stop. Or maybe it happens to get in contact with some water and blow through the surface. Thanks for the update.

    1. My question is: since we are not seeing many earthquakes or tremors at the spot could this all be happening at a much deeper, less brittle, layer of the crust and the shallow quakes we’ve had only reflect some icecap adjustments?

      1. Grímsfjall is rather smooth volcano, as it erupt frequently. That means that the rock is less brittle and a lot softer. So we get fewer or no earthquakes before a eruption.

        But when the eruption starts, there is going to be a swarm of earthquakes happening just before the eruption.

      3. Is that why the slope of the seismic energy is lower this time around?…

        Is the lower slope indicative of an earlier precursor to a larger event? …

        Should we expect a drastic change in the cumulative seismic energy before an eruption is indicated?

        For a “history repeats itself” scenario, it isn’t satisfying.

        Vatnajökuls Cumulative seismic moment (frame grab)

  2. I have 3 volcano sites bookmarked now, yours Eruptions and The volcanism blog.

    Grimsfall makes Katla seem like a baby and EJ a mouse, lol.
    I feel that the Iceland “hotspot” is one large volcano too and what happens at Grimsfall, Katla and EJ is just part of an eruption so large, that if from satalite, video was recorded over 1 million years and played back fast it would look continious.
    From a distance not a place one could farm land, yet Icelanders manage very well.

    Look forward to the next eruption in Iceland (hope its a small one by iceland standards!) With you, Fireman, Gummiey and others we are well placed to get all the action fast.
    Kind regards,
    Russ. Isle Of Wight, England, UK.

  3. In Northern California… and elsewhere, there is a phenomena known as “silent quakes” where the ground moves but doesn’t quake. I don’t know if it generates what would be interpreted as a tremor when it does that. While the mechanics might be different, we might be seeing that here… with the motion being a plastic like oozing of the stress through the area as the formations shift to accommodate the pressures.

    Just a thought.

    And it does not explain why it the GPS would tend to do something like this every year. That points towards a seasonal cause, like glacial melt or some other thing like that. I also would not expect it to have a tremor component since near surface material isn’t generally in a plastic state. Hard, brittle material would cause pops and snaps… you know, making quakes.

    Now… if it’s deep oozing material, what happens when it reaches a zone with less pressure and it can actually generate melt? That could make things quite interesting.

    1. @Lurking: Looks like today is “good discussion day”. Maybe you are needed a the other blog. I must take leave for now. See you guys later.

    1. i hope You were putting the fire out and not walking across the smoky roof.
      Best!motsfo

  6. Well, as SIL has noted about these charts, they don’t really have any use outside of comparing one station with itself. I do know you can fudge a comparison by taking the amount of relative change and then comparing that amount with another station, but you have to be really flippin careful that you don’t read too much into it since different pieces of gear have different gain curves. Thats just simple electronics.

    With that caveat in place, it does seem that whatever it is shows up better on Faguholsmyri since all spectra climb at about the same time and with the same intensity. Station KAL sees the low end spectra quite well, and has less of a response at the higher frequencies.

    The problem child is SKRO. SKRO has a high frequency bump and a lackluster upwards trend of the low spectra. That makes no sense to me. It could be oddities in the gain of the different channels, but at other times they seem to respond at about the same rate as the high channel.

    In a nutshell… IDK.

  7. BTW, Faguholsmyri is down by the coast, South of Vatnajökull and SKRO is west by northwest of the glacier complex west of Bárðarbunga and somewhat north of Hamarinn.

  8. What’s with the little “glitch” in many of the tremor plots? It’s like a skip of a heart beat the the regular rythm returns its not very large but its on many of the plots

  9. Lots of fun trying to read tremor plots. Thank you Jón. Thanks for the comparison charts, Raving, and the remarkable remarks, Lurking. (Occasionally I let my posts get Google translated back to Portuguese. You should see how this one, with all pleonasms and translated nicknames, sounds funny.)

  10. I have made a map of Iceland myself with all stations marked so that I can see where activity is taking place. And yes, Fagulholsmyri is right where Lurking said. Hope there isn’t a volcano there: I would have such a hard time memorizing it… How can you póssibly pronounce this?

  11. I can’t… but the three letter abbreviation means something not politically correct in US English and though I don’t personally really give a … “hoot”, it’s not my blog or my place to ruffle any feathers. So, I took the effort to try and get it correct from the SIL image. (it wasn’t in the GPS list).

    And yes, there is a volcano nearby. Öræfajökull 64°00′N 16°39′W

    “It is the largest active volcano in the country and on its north-western rim is Hvannadalshnúkur, the highest peak in Iceland. Geographically Öræfajökull is considered part of the Vatnajökull glacier and the area covered by glacier is inside the bounds of Skaftafell National Park.”

    While Grímsvötn and Bárðarbunga are monsters unto themselves, you don’t get to be the “largest in the country” by putzing around.

  12. Hmm.. reading back at Renato Rio’s post it looks like I need to be more careful with my colloquialisms.

    By “flippin” in that context, I mean “really really really” careful.

    “putzing” .. intended meaning, “idle”.

    “hoot” … err.. “care” or “concern”.

    “ruffling of feathers” – upsetting someone.

    “yonder” – “over there” … Wait, I didn’t use that. Never mind.

  13. I think there is harmonic tremor going on both near Katla and Grimsfjäll….

  16. Looking at the examples posted by Jon earlier it does seem that SNB and HVO tremor stations are emitting a clear spike in harmonic tremor.

  17. Hey Jon, just found your excellent website. So I have a question. Does this mean Grimsvotn could erupt before the end of the year? Or could it deflate and go back to being dormant?

    2. At this point Grímsfjall can erupt at any time. Volcanoes can do that. But given the history it seems unlikely in the case of Grímsfjall volcano.

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