Strong tremor signal detected at Grimsvötn

At 19.03 local time the automatic SIL-system in Iceland picked up a strong tremor signal. When this type of tremor signal is visible in Iceland it is normally associated with either a large jökulhlaup (rapid glacial melt outflow) that can become larger than the output of the Amazon River, or it is associated with an eruptive sequence.

In the afternoon there was a moderate swarm of earthquakes between M1 and M1.5. Most of the earthquakes was not visible on the automatic detection system due to disturbance from the current bad weather in Iceland.

The signal conforms to it either coming from Grimsvötn or Thordarhyrna central volcanoes under Vatnajökull.

We are not stating that this is an eruption, just that it is a confirmed strong tremor-signal. As always we await confirmation by the Icelandic Met Office and other relevant Icelandic authorities.

We will update this one as we get to know more.

Update: There is a lack of low frequency tremor in the seismic signals indicating that this may indeed be related to a Jökulhlaup. But, we will have to wait and see. The seeing part may though be a bit elusive since it is in the middle of the night, and that there is bad weather in Iceland.

CARL

20 thoughts on “Strong tremor signal detected at Grimsvötn

  1. 🙂 this will make a nice impact on the cumulative plot.
    Im also excited for the up – comming Grimsvötn article.

    By the way, no red dots on IMO yet…
    If its Grimsvotn caldera and not Thordarhyrna,
    It coud be because magma is trying to get through the caldera roof in some weak spot.
    I apologize for alot of talking… Im excited

    • There are a number of earthquakes that have not shown up on the earthquake plot due to weather disturbance. Iceland is currently in Orange Weather Alert.

    • Jesper, these are too small to be noticable in the cumulative plot. You need something like M2.2 and higher to make a visible little jump in the plot. That said, the number of quakes is really starting to increase. As for today’s signal, lack of low frequencies in the tremor signal suggest a jökulhlaup rather than an eruption. I suspect we have to wait a little longer, but not too long before the real fireworks start.

  2. This was written 16/9-2019, but the notice is still up
    “A small glacial flood is still ongoing in Skaftá river. The flood comes from the Western Skaftá cauldron, but last time a glacial flood came from there was in August 2018. Therefore this is not expected to be a big flood. People are advised not to stay close to the source of the river for long because of potential gas pollution. The river is monitored 24/7 at the Icelandic Meteorological Office.”

    • Yes, but this is not related to that small hlaup. Judging from the signal my current thoughts are that this is a Grimsvötn hlaup, but not a major one.
      But, we will have to wait and see.

  3. Now that the initial signals have declined a bit it looks like a jökulhlaup from Loki-Fögrufjöll.
    I must admit that I am a bit miffed about this. Nice strong tremor, but no cigarr.

    • That is interesting. There were some earthquakes there (Hamarinn) mid August and at that time it was pointed out by Jon (https://www.jonfr.com/volcano/?p=8054) that previously, such activity had been followed by a jokulhaup a few months later. This time again, apparently.

      Another volcano to keep an eye on. It hasn’t erupted since 1910 (apart from some presumably hydrothermal activity).

  4. Sorry to pop in with a slight off topic (which may have already been covered here recently): we’ve had three days of purply sunsets here in the UK, with a positively Prince-esque one this evening. Anybody here know it’s confirmed volcanic, and who the culprit is? Cheers in advance (people who know my volcanofetish keep asking me!)

    • Most likely not related to volcanic activity, even if several have tried to blame a minor eruption in Kamchatka for it.
      It is more likely to have its origin in the large scale forest fires that is running around the globe. Which is really sad news.

        • I clearly saw this deep purple sunsets in Scotland too.
          There has been a deep high pressure across the UK, so whatever it was high in the atmosphere came down and the dust caused the beautiful sunsets.

          The question is between the global fires and Raikoke, which one is the culprit?

          There has been widespread fires in the Amazon again (not reported in the news) and also in southeast Asia/ Indonesia (just barely reported in the news) but the haze in southeast Asia has been quite big news locally.

    • Probably pollution – we have had them here in the Western Isles. Nowhere can escape it nowadays!

      • Hamarinn drumplot 2.0 hz. The tremor lasted about 38 minutes.

        Credits IMO.

        [img][/img]

    • The plot is based on registered earthquakes. Anything that gives a dot on the map that falls inside the rectangle 64.27 – 65.54 deg N; 17 – 17.5 deg W, has a magnitude larger than M1 and has been manually confirmed (quality 99.0) will count.

      Now, we have concluded that this was probably tremor from a jökulhlaup, but even if it had been actual volcanic tremor, it probably wouldn’t show up as an earthquake on the map and thus would not affect the plot.

      Another thing to notice is that the unit on the y-axis is in Nm. That means it is the sum of the seismic moment from each quake that has been registered. Note that the magnitude that we see in the quake list is a logarithmic measure of the seismic moment. This means an M2 will give around 30 times larger rise in the plot than an M1 and since M2 is just noticeable in the plot, it means that we need a lot of M1 quakes to make a visible jump in the plot. The sum of all quakes in the last 48h is equivalent to something like M1.8 and gives, as you say, just a tiny change in the plot.

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