Grímsvötn / Grímsfjall rising fast according to GPS data

According to GPS data from IMO (automatic data). It appears that Grímsvötn / Grímsfjall are rising fast. But current inflation according to the GPS data is now 80mm. But was around 70mm few days ago. Given this GPS data it is clear that Grímsvötn / Grímsfjall might erupt sooner then estimated by the geological scientists in Iceland. But they where expecting a eruption in Grímsvötn / Grímsfjall later this winter at earliest.

It currently is impossible to know when Grímsvötn / Grímsfjall is going to erupt. But given the GPS data at current time it is going to happen sooner rather then later. It is clear that Grímsvötn / Grímsfjall is worth keeping watch on, as a eruption can happen with little or no warning at all.

8 Replies to “Grímsvötn / Grímsfjall rising fast according to GPS data”

  1. For future reference regarding this information, , on the current Big Think Eruptions thread, a timely link from M. Randolph Kruger 8;50 A.M. for MODIS thermal satellite readings…

  2. @ Jon – As I have already said thank you for an all Icelandic volcano blog. It really is interesting and I will surely follow it closely.

    Regarding the Grimsfjall impending eruption. How does it usually erupt? Is it explosive? I read somewhere that last time it erupted ash reached quite alot of altitude. Is there a risk for airspace shutdowns when Grim erupts?

    Given the fact that it is a subglacier volcano i guess that by its nature it cannot have effusive eruptions..

  3. Daniel_swe, When Grímsvötn erupted in 2004 there was no airspace closure expect in Iceland and then it affected domestic flights only. It is only explosive eruption when it is under the glacier. But fissure eruptions can be a different matter if they happen where there is no glacier (Laki eruption).

  4. Lurking posted an interesting plot of stress for Grímsfjall which included the curve for the previous eruption. Currently, stress levels at G is at about 80% of what they were when the previous eruption began. Judging by the increase of stress over time, Lurking’s plot identified March-April 2011 as when the crisis point would be reached, but that assumes that increases in stress levels remain linear. If I recall correctly.

  5. “But they where expecting a eruption in Grímsvötn / Grímsfjall later this winter at earliest.” So we should expect an eruption early this winter at latest, which means, during the next three months counting from now, which means, Xmas fireworks!
    Jón, I understand that, besides a strong 5 earthquake, we won’t be able to know when the eruption will start, unless some recognition flight goes to the spot or else, if there is a major jokülhlaup down Vatna, am I right? And is it possible that a fissure eruption could occur to the west, I mean, outside the glacier telling from current GPS measurements? Thanks.

  6. @Henrik

    You are correct. But the base plot is not mine Iceland’s professional seismo/geo guys made it. There are a few caveats with how to interpret it.

    The 90% line is completely arbitrary. It was chosen as a reference.

    Being at an 80% level compared to the last eruption is an accurate read, the part about that chart that really like is that they keep it updated.

    When or how the rocks fail and create the next eruption, you just can’t accurately predict. I did some reading on that moment tensor value and get what seems to be a different critter than what they are plotting… related, but different. The Wakipedia article denotes it as M0, and the chart uses M1 . This probably means that it’s not the same. The M0 calculation relies on the shear modulus, area of the rupture, and the average displacement. I’m guessing that they are tallying it up for each quake. I took the coordinates of their bounding box and plotted it vs the extents of the volcanos in the area… It is specifically centered around Grímsvötn.

    That’s important. Hence the bold. That means that the ongoing “swarm” at and northeast of Bárðarbunga and the Hamarinn events are not making it into that moment tensor chart.

    If you will remember back, there were a couple of posts over at Eruptions that brought up the subject of an odd “non double couple” event at Bárðarbunga. That linked article then went on to describe what appears to be a two layer magma chamber… or at least two theories of how things might be oriented beneath the volcano that would explain the waveform. This was because the quake event generated no specific offset like most quakes do. A crude summary is that the waveform seemed to indicate a vertical movement of something, and then a subsequent filling of where ever that something was with surrounding material. Could have been magma, could have been hydrothermal fluid.

    The part of that paper that I found revealing was that after all that shake, rattle and roll under Bárðarbunga, Grímsvötn erupted. A later paper (the one discussing the magnetic anomalies) mapped out the structures of the area and noted that they essentially consist of a main central volcano and a sibling… each having different ejecta consistencies, but sharing the piping. The main ejecting less modified magma (more mafic) and the sibling ejecting magma that has been modified/evolved. This points to the magma spending time under the sibling before it actually erupts.

    Here’s the rub. Grímsvötn is not Bárðarbunga’s sibling. Harmarinn is. Grímsvötn is another central volcano in siting in it’s own fissure swarm area, and it’s sibling is Thordarhyna. However, that paper also notes that Grímsvötn and Bárðarbunga do share some fissures (dikes) that run up and intermingle with each other. That was apparently what happened in the 1996 non-double couple quake that later generated an eruption.

    So… long winded here, sorry.

    My read is that sure, that chart is handy, but it’s not a fullproof indicator. Volcanoes are sneaky like that.

    The Puzzle of the 1996 Bárdarbunga, Iceland, Earthquake: No Volumetric
    Component in the Source Mechanism

    by Hrvoje Tkalčić, Douglas S. Dreger, Gillian R. Foulger, and Bruce R. Julian

    Volcanic systems and calderas in the Vatnajökull region, central Iceland: Constraints on crustal structure from gravity data. by Gudmundsson, Magnús T.; Thórdís Högnadóttir

    Sorry, no direct link to the paper but it’s out there somewhere, that’s how I got it.

  7. And now about the GPS info.

    I was summarily whacked up the side of my head earlier when I noted the GPS elevation rise.

    It was a well deserved whacking, I forgot to look at the historical trend.

    Yes, GFUM is showing a strong definite trend in elevation.

    But it does that every year.

    So, the question remains… does it mean something? In fact, what causes that? I would think that its an unloading of ice, but that’s a lot of movement… does the crust respond/rebound that strongly?

    At what point does this annual relief in stress cause enough additional magma to form and trigger an eruption?

    Winter might not be a bad prediction when you consider that.

  8. Okay… this is probably the ugliest chart I have ever made. Not that there is anything ominous about it… it’s just one ugly chart.

    See, I don’t have access to any actual data, so I’m limited to what is publicly available. Not that I can do anything more with it, except for making a prettier chart.

    This is the GPS chart linked earlier, imported and a VERY crude eyeball interpretation placed on top of it. I did that so that I could get some measurements. The current rise in elevation is LESS than the rise that occurred back in 2008. 111 points vs 140+ points (mm). This is as measured from the average previous trough. Another thing that I noticed while fiddling around with it, is that there seems to be a double peak that occurs on a regular basis. of the last four peaks, three of them show that, while the last one seemed to be … \confused.\ I’m guessing that this has to do with flooding events or ice movement… remember this is all on a glacial ice cap, and how the ice and the volcanoes get a long is about as easy as predicting how a cat and a dog in a box will get along. It usually doesn’t end well.

    Anyway, here’s the chart, make of it what you will.

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