Odd strain at Hekla

Photograph by Eggert Norddahl, used under exclusive permission. All rights reserved. To use this or any other image by Eggert, contact Volcano Cafe or Eggert Norddahl directly.

Hekla have one of her days today. It all started at 08.56 with a small earthquake located at Árnes close to Haukadalur SIL-station. The earthquake was clearly tectonic and at a respectable depth of 6.2km. The earthquake will most likely be revised later as it is of low probability due to low energy released. What makes this earthquake interesting in relation to what followed is that during the weeks before Hekla 2000 the area had a small number of low energy earthquakes.

Image by Icelandic Met Office (IMO). Location of the very small earthquake that started todays festivities.

A couple of minutes later the new (installed after the 2000 eruption) borehole strainmeter at Hekla registered a medium sized, but long lasting negative mountain strain transient. During the last eruption the largest recorded strain was recorded at the more distant Búrfell. The idea of installing Hekla borehole strainmeter was to see if it is possible to pick up pre-cursor strain falls. As I am writing this the negative drop in strain is still ongoing.

Image by IMO. The initial stages of the mountain strain recorded by the Hekla Borehole strainmeter.

A couple of small spikes are showing on the Mjóaskard SIL-station, but they are to small to pinpoint them as earthquakes, at least the exact location. Also, a small tremor ranging from 1,5Hz and upwards started at 11.35 local time.

Image by IMO. Strain at -6E+04 and counting. Negatve mountain strain building up.

Is this then the run up for an eruption? Sofar it is not likely. We still miss the tell tale swarm of small earthquakes (0.2 to 2.0M), a large negative strain drop at Búrfell borehole strainmeter, and of course a rapid increase in harmonic tremor on all stations. This can though change at any time. As mountain strain builds up the likelyhood of earthquakes increase over time.

I would not recommend climbing Hekla today.



263 thoughts on “Odd strain at Hekla

  1. I would love for Hekla to go bang sometime soon but I hope not in the next month – a lot of my friends are going on church mission trips during that time and I would hate it if some of them couldn’t fly out or got stranded somewhere.

    • I wouldn’t be very funny neither for the people living in the south of Iceland, if it were a bigger and / or ashier eruption, like Irpsit eg.. 😐

      • Inge… Think about it, Irpsit would run out of his house in his swim trunks and a gas mask to get ash samples, pictures from a distance and so on. He would also take pictures of Islander blasting past in his car on the way to Hekla. You know, they are volcanoholics :mrgreen:

      • Actually I start having a strong bet that Hekla will erupt within the next weeks or months. I think yesterday odd strain is a preliminary sign. But I wish that any eruption is just small and with little ash but nice lava fountains. But little fluoride please.

  2. @DFMorvan from up above:
    It is a massive copper bearing sulphide (3.5 – 5 percent on the surface of the layer).

    Edit: With the usual metalic impurity for the ore zone.

  3. Continuing the VEI calculation meme.

    As mentioned, that paper and the formula(s) from it… uh, hang on.

    (it might help if you had your own version)

    .., that paper is geared toward mass ejection rates based on sparse data. About that sparse data and how to get something useful out of it.

    VAAC reports are probably the most handy reports available for any given eruption. VAAC is most concerned about keeping aircraft from plummeting out of the sky, so they try to stay on top of the hazard. This also means that their reports, though good, are more focused on the threat than the volcano. What the volcano is actually doing is little concern for them… what it did do it most important. This means that once a plume is lofted into the air, the max elevation of the plume sort of remains fixed until it dissipates. The threat envelope will move around with the cloud… and generally the max elevation will remain mostly fixed.

    If you are lucky, the VAAC report will state somewhere in the warning what the plume height is over the volcano. That is the data that a volcanophile will keep track of. That gives you the current state of the eruption.

    Taking the time stamps for each report, along with the height of the plume over the volcano, and adding in the heights and time stamps from what ever geological agency reports, you can get a pretty decent record of the activity levels, and make a rough estimation (using Mastin et al) of the total amount ejected.

    You do this by interpolating the rate from one data point to the next. You could connect the dots using a straight linear trend, or you could use some sort of poly curve or cubic spline (what ever your spreadsheet or data fitting program is capable of). From this curve, you need to get the interpolated increments down to one second intervals. Once you have interpolated timestamps and the extimated column heights at those moments in time, apply the Mastin formula to determine the DRE rate.

    Then you just sum those rates in order to fabricate the total amount erupted to that point in time.

    It may sound complicated, but it’s pretty straight forward.

    From Mastin et al

    H = 2 * V^0.241

    Solving for V

    V = (H/2)^(1/0.241)

    V = Rate in m³/s
    H = Height in km.

    And.. a very important caveat… the formula has an error envelope of a factor of four. That’s pretty large, but it gets you in the ballpark for eruption estimates.

  4. And now a gripe…

    JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 102, NO. B9, PP. 20,087-20,091, 1997

    A proposed volcanic sulfur dioxide index (VSI)

    C. C. Schnetzler et al

    #@#$ paywalled asshats.

    • Okay… now that that is out of my system.

      A bit about gas. Specifically, SO2.

      SO2 is a volcanic gas (along with a lot of others) but specifically , SO2. SO2 is a high heat product… H2S is a low heat product. You can tell the difference by the smell. Burnt match smell, SO2, rotten eggs, H2S. Don’t run around sniffing for them, both can be lethal, and H2S deadens your sense of smell. SO2 turns to acid in your mucus membranes… specifically H2SO4. And that’s not a good thing.

      But… that H2SO4 bit is important.

      In the troposphere, where all the weather happens, H2SO4 yields “VOG” .. “Volcanic Fog.” In LA, they coined the phrase SMOG… essentially the same thing but with a little auto exaust thrown in for good measure. It’s a pollutant, and tends to trap heat.

      In the stratosphere, up above where all the weather occurs, H2SO4 acts as an umbrella, blocking sunlight and cooling things off.

      A couple of days ago, a paper was linked here that addressed this issue, and noted a seeming connection with CO2 and the scavenging rates of both gases from the atmospehre by OH, the friendly hydroxyl radical. (it is the pre-eminent free radical that we try to avoid in our diets)

      Side Note: Nitric oxide - NO, is the other one
      that we are usually concerned with ... oddly enough,
      it's also the active ingredient in Viagra. So if you
      are shunning free radicals in your diet, but are
      munching Viagra, that sort of defeats the purpose.
      At least you will enjoy yourself.

      Now… it’s been a lot of years since I took chemistry, but I was trying to figure out the dynamics of SO2 to H2SO4 production. I used several chemical equation balancing programs… but they all come up with a weird issue in the of O2. Looking into it, it turns out the SO2 + H2O will produce sulfurous acid and not sulfuric acid. In order to get sulfuric acid, there has to be a catalyst. If you remember, a catalyst enhances a reaction rate though it is not destroyed by the reaction. (such as the platinum beads in your cars catalytic converter). In this case, the major catalyst is NO2, or Nitrogen dioxide. Nitrogen dioxide comes about from the O2 (oxygen) and N2 (nitrogen gas) reacting in a high heat environment… such as lightning strikes, combustion engines, and volcanic eruptions.

      When an eruption occurs, there is an emission of SO2, it gets converted over to H2SO4, and if it makes it to the stratosphere, acts as a radiation shield blocking sunlight. How much gets that high up, depends on how much is released in the eruption, how fast it gets leached out of the column by the ambient humidity and the availability of NO2. That that is leached out of the column becomes tropospheric H2SO4 if it leaves the column and doesn’t make the trip the rest of the way above the tropopause.

      I read a paper a while back… don’t have a link to it, but the paper indicated that tropical eruptions have a much greater leach rate than the higher latitude eruptions. They also have a thicker troposphere to punch through to reach the stratosphere.

      Latitude vs Holocene Volcano Count

  5. To everyone but for someone that wants to find out these mystery eruptions:

    I have now about 10 spots which I photographed soil sections containing the ash layers.

    These are located mostly around where I live (west of Hekla, also in south of Langjokull, and near Hengill). In addition I also took several of them as I travelled to Snaefellsnes peninsula.

    I saw many interesting things, but interestingly I found a thick old white-grayish pumice layer in a spot 5km east of Hengill; that pumice was so well that it even floats in the water if I removed it from the layer. I don’t think that comes from Hekla (which is 65km from this spot). That band was thick and at about 35cm deep.

    The bands from my previous posts are located 15km further east (in direction of Hekla, and near to it, about 50km from it). The only bands I found here at that depth are the mysterious grayish layer and the thick white band I identified as Hekla 3 (circa 1000 BC). What if the pumice detected near Hengill is the same that the mysterious gray layer. They look likewise in apperance and depth.

    Now, you come think this came from Hengill, but the interesting thing is: in Akranes, Borgarnes, and the entire Snaefellsnes peninsula I saw many thick white and grayish bands of pumice, which came obviously from Snaefellsjokull. In the entire peninsula thick bands are visible, some contain well preserved pumice of white and others of gray color. These bands are several but one or two are still well visible in Akranes, which is about 100km of the Snaefellsjokull volcano (this is already nearer to Hengill), there I can find also some chunks of grayish pumice that were well preserved.

    Now, it’s a mess in my mind, because I don’t know whether the largest plinian eruptions of Hekla reached that far, or whether the Snaefellsjokull eruptions reached also that far, or even the third possibility of being pumice from unknown eruption of Hengill or Langjokull. Whatever is, dates probably 2000 to 3000 years old, judging from the depth, but it is so well preserved. I have heard that Hekla pumice is one that does not preserve well. So this pumice is the first mystery.

    The second mystery: Between Akranes and Hengill I see also a significant orange band just above that pumice band, at about 25cm deep. It is probably something like 1000-2000 years old. I don’t think this is the Vatnaoldur settlement ash, but I might be wrong. Because if this is not, then it is something else, and it does not look like one of the obvious Icelandic volcanoes. Curiously near Ljósfjall in Snaefellsnes peninsula I found several (about 4) of these orange layers. But this volcano is not known for having such a large eruption that could have sent ash so far away. So, that orange band is my second mystery band.

    Last possibility is that these bands could be same eruptions of a different colored band in another place, but just because of these chemical erosion, they present different colors at different spots, as well as different depths. That makes my mind spin.

    In pic, taken near Hengill, one can see first 3 layers of white ash (probably Hekla), then an unknown orange band and the thick white-grayish pumice at the bottom.

    My plan is to write a part III with all of these updates. But I feel so lost with layer identities, that I cannot write a coherent piece of information, without resorting to present it first.

  6. D I N G !

    Not the paper that I was after… but just as good. Specifically, table 3-2. VSI to VEI.

    VSI was designed to fit the VEI scale so that you could get a quick and dirty, but relatively reasonable estimate of the SO2 emission of a Volcanic eruption. The scales are different for Arc (such as Tongario) and non Arc volcanoes.

    “Chapter 11.A Volcanoes -EMEP/EEA emission inventory guidebook 2009”


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