Hekla – GPS variance

I just could not stay away from this picture. It is just to stunning.

For those who need a brusher up on Hekla I recommend reading the two posts that is linked below if you need a refresher. The first one is a rather traditional write up about Hekla; the second is a revision of how I interpret Hekla based on Papers by Sturkell and Carmichael respectively.



In short one can say that even if Hekla good at being hard to interpret she is rather consistent in her uplift between the eruptions. So far it has been smooth going from the 2000 eruption up until 2012-01-30.

Back then we had a period of activity in and around the Saurbaer area with small scale tremor, a few minor earthquakes ranging from 0.2M to 0.7M and some microseismic activity. That was then interpreted as hydrothermal activity in the area.

As that calmed down we then got an earthquake of 1.2M at shallow depth in the topmost part of the fissure at 0.1km depth. The focal point of the earthquake was exactly at the 1947 eruption center.

For being Hekla that is a lot of activity in a short time.


A few days ago I looked through the GPS-plots of the network that the Institute of Earth Sciences runs under the supervision of Sigrún Hreinsdóttir. Without the gracious release of that data publicly it would not have been possible to do the plot below.  All copyright to the data used is held by the Institute of Earth Sciences and Sigrún Hreinsdóttir respectively.


On the various GPS-plots I noticed that around the first of February a marked deflation started at several of the stations around Hekla. Due to the complexity and sheer number of stations I could not get a clear picture, so I enlisted the help of the master of plotting, GeoLurking. Any mistakes in the interpretation of the plot are entirely mine.  GeoLurkings plot is a daily average trend line for the period 02-01 to 02-18.

“This is the daily linear trend based on the interpolated available data from 1 February to 18 February. It was then re-grided with a quadratic poly sheet at 255 x 255 in order to obtain the fill    between stations points. Purple is -1.2 mm/day, red is 0.4 mm/day. Green is -0.26 mm/day.” (GeoLurking, 2012)


Image by GeoLurking. Please click on the image to get a bigger version.

There is due west of Hekla a clear center of hard deflation (purple), there is also a marked deflation NNW that is deflating rapidly (dark blue). From the last spot there is a pale blue band running over the northern part of Hekla proper.

On the southern part of Hekla central volcano (green) there is a small deflation going on.

Regarding the parts with inflation (red 0,4mm daily) there is no surprise that the area up towards Búrfell is inflating, it has been doing that for a long time. What is though surprising is that this trend continuous even though all of northern Hekla is deflating. This inflation has been interpreted as being a dyke emplacement running from Hekla. That is starting to look a bit less likely with this data.

What is brand new is the well defined inflation hypocenter west of Hekla. This is an unusual spot for activity at Hekla since it would be outside of the regular fissure of Hekla.

The red part seen towards Vatnafjöll is equally surprising since Hekla and Vatnafjöll has never during the last 10 000 years erupted at the same time. When Vatnsfell is active, Hekla goes dormant. And do not make the mistake of believing them being the same volcano, or even volcanic field. Vatnafjöll is erupting magma normal for Iceland, and Hekla is erupting lava associated with subduction volcanoes. So the link is mechanical only, probably some kind of pressure release function. The inflation at Vatnafjöll might therefore be a sign that Hekla is nearing the end of its 1 000 year long cycle of high eruptive pace, but that is highly speculative at this stage.


Hekla is known to have more than one chamber, as many as nine major chambers has been suggested in various papers. Be that as it may, Hekla has complicated innards, and it seems like magma can run freely between the chambers. In any other volcano on Iceland a displacement of this large amount of magma would be associated by continuous large scale harmonic tremor and numerous seismic events and here almost nothing of that has been evident.

From the looks of it a possibility is that Hekla would be more likely to have a flank eruption this time, or even a new fissure opening up in parallel to Hekla. If so, it would be the first time that has been observed by humans. One should though note that the Litla Hekla Fissure is in that direction, and that the inflation center is right on top of yet another fissure. So I guess it is not totally out of the question.

All of this should be read with a large caveat in the back of the head, any interpretation of a volcano is most likely wrong in parts. This is the least reliable volcano on earth, so all of it might end up being wrong.


192 thoughts on “Hekla – GPS variance

  1. And the answer seems to be Eyjafjallajökull…
    While people have been guessing about Godbunga, Hekla, Katla, Tindfjallajökull and Torfajökull, the answer seems to have been Eyjafjallajökull all along.
    Smjörgil SIL is currently recording a harmonic tremor spike that started a few minute before an 1.8 Earthquake occured at Eyjafjallajökull. During the last 2 months there have been a few asymptomatic Earthquakes inside the volcano. And also there have been on and off harmonic tremoring for a week now.
    Todays activity is magmatectonic to magmaseismic in nature. This is pretty much the first signs of life sine the 2010 eruption ended. The earthquakes during the last two months have centered around the crater, or inside the Fimmvörduhals area.
    Please note that there is high wind in the area, but the level of harmonic tremor far succeds the energy levels during tonights storm.


  2. Are you saying that this gas is from say weeks ago that the people are smelling now.

    What I dont understand is that this smell has only been reported in the last couple of days and it was noted especially after one of the latest earthquakes in that area.

    Could it then be that the small quakes are fracturing the ground and the gas is now escaping but is this not something that could be poisonous ?

      • I took a trip up Mount Teide on Tenerife once and could smell sulphurous gases. I’m sure it’s not going to erupt soon – but it’s just part of normal volcanic activity, as Carl suggests.

    • I know that spelunking is a activity that occasionally occurs due to the many caves on the island.

      One thing that explorers should do, is to make sure that the cave has been checked to be gas free, or that they have the ability to check it as they go.

      Any sealed closed space on a ship (USN) has to be checked before it can be entered by workers once it is opened up. Something as simple as a sandwich that had been left in there can kill you. (decomposition gases)

      So, with a volcano seeping gas, caves are a natural location for them to accumulate and to remain in high concentration.

  3. There was some steam above the stain this morning thank goodness I was not seeing things!!

    ER comment.

    Update 24/02 – 11:36 UTC
    – an additional earthquake occurred at 09:16 and brings the total to 4 today.
    – The image below is quiet spectacular. We have some faint jacuzzi since this morning, but the distorted image above the vent shows that the total wide of the picture (wide angle at the moment) has a higher temperature than the rest of the sea. We haven’t seen this since a while ! The image is showed as captured from the webcam.

      • One should remember that the Roques de Salmor is the spot where there was gas spurting out of the old underwater lava tube. And that had them shut down the Tunnel due to gas levels and declare the area off limits. I later stoped and the area was opened up again.
        I would not rule out gas seaping out there from time to time really.

        • Oh, you all have to be kidding! Whether the odors eventually mean anything or they just go away, doesn’t matter. The point is, the people are reporting odors that have not been present before! If they had been present for 100 years, they wouldn’t be reporting them as something new they have just noticed! Also, I remember when this board was extremely interested in whether the cave systems under this island were being monitored for gases. Gas smells are significant. If they are being reported truthfully, then by what means are they suddenly available for being smelled?

          Judith, you rock, keep reporting.

  4. Am I alone in the after-work-sheepish-bar today? Just grabbing a beer and wishing you a great weekend everyone! Btw, I counted my amount of visits here today to 12 :O – crazy isn’t it? 😀


  5. Pero AVCAN, Elsa está hablando de una mancha que, cuando está, huele… eso significa que ya se está expulsando algo por el norte como pasa en el sur ¿o estoy equivocada? Gracias

    But AVCAN, Elsa is talking about a spot, when you are, smelling… that means that already it is expelling something to the North as it happens in the South or I am wrong? Thank you (Translated by Bing)

    Avcan FB Comment https://www.facebook.com/profile.php?id=100003048369129

    En una de las expediciones del buque Ramon Margalef hablo ante las cámaras de televisión de expulsión de gases y nuevas coladas en la zona de arenas blanca en Frontera, máximo 3 kilómetros distante de ese punto que ahora se nombra que fue el punto principal del segundo enjambre sísmico hasta el sismo de explosión que luego desembocó en la mayor fuerza de expulsión por la restinga. ¿Es posible que en la foto satélite de hoy se pudiera distinguir si existe?. Si se tuviera acceso a los sismógrafos ubicados en Frontera ¿Estos acusarían un tremor por una posible salida de gases?. Gracias de antemano por las respuesta a mis preguntas.

    In one of the expeditions of the vessel Ramon Margalef speak before television cameras to expel gases and new lava flows in the area of arenas white border, maximum 3 km distant from that point which is now named it was the main point of the second seismic swarm until the earthquake of explosion which then led to the greater force of expulsion by la restinga. Is it possible that the satellite photo of today could distinguish if it exists?. If access to the seismographs located in border do these acusarían a tremor by a possible exit gas?. Thanks in advance for the answer to my questions. (Translated by Bing)

    about an hour ago · Like · 5

  6. ER are reporting activation of the volcanic activity.

    Update 24/02 – 14:48 UTC
    – We have a clear reactivation of the volcanic activity
    – a faint jacuzzi is present all day long
    – HT seems to pick up a little bit
    – 5 earthquakes today
    -Ramon Margalef is still cruising not only in front pf the coast, but also near the main vent

    Ramon Margalef with faint jacuzzi in the background

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