Icelands forgotten Volcanoes

Eldgigur seen from the Hágöngur volcano.

Sometimes a bit of honest digging will pay off in the oddest ways. Trying to utilize an unexpected free day I decided to find an alternative explanation for the uplift associated with the Hamarinn volcano. A long shot as good as any other to pursue on a rather grey day.

While on the prowl for this unknown central volcano I got a lead, and started to dig. To my surprise I found an old (1952) geological report from a Danish survey that seemed to have something to do with my suspected culprit. To my utter surprise it was about another equally unknown volcano. And as if this was not enough, it also named a few other volcanoes I had never heard about.

Image taken from the linked paper below. It shows very well the Grimsvötn fissure swarm as it goes to the SSW through Thordharhyrna volcano.

As you can see on the image the top most volcano is one of the more infamous on Iceland, Grimsvötn. And that one does not merit a lot place here, more than the obvious mentioning of its southern fissure swarm that ends up in Laki. Most of you know already that Grimsvötn was the responsible parent volcano for the Laki rifting fissure eruption, and that Thordharhyrna erupted simultaneously with Grimsvötn and Laki.

But hand on the heart, how many of you knew about Háabunga central volcano? Well, some of the more volcanoholic of the readers of this blog probably do know about it. I did at least. Also Thordharhyrna is well known, but there the fun probably ends for the readers of the blog.

SSW of Thordharhyrna resides a volcano I never had heard of before, Geirvörtur. About this one I cannot say much, at least more than that it resides on top of the Grimsvötn fissure swarm, and that probably is a remote sub feature of Grimsvötn.

SSW to Geirvörtur we have the 1200 meter high volcano of Hágöngur. And know it is starting to get really exiting. Close by to Hágöngur is the SE is the 854 meter high post-glacial volcano of Eldgigur. It resides on the Grimsvötn fissure swarm, but it is doubtful that it is magmatic subset. This is due to the rather odd nature of the lava.

Eldgigur seen from the other side.

Technically this is a very large scoriae cone, at the top resides two small and one large crater. Only the larger crater has produced a minute lava flow. The rest of the volcano is built up of 3 layers of different lavas showing as 3 concentric slag walls.

The cone is built up by very fine grained material filled in with bombs. The first type of lava is a black plagioclase containing phenocrysts of clinopyroxene. The second layer is a grey more evolved and crystallized lava that is translucent. It is a type of plagioclase-porphyric lava. The third lava is named as bytownite, be that as it may, the content of iron is high in the red lava with 15 percent by volume. Inside all 3 types of lava are found layers of clear colorless olivine (forsterite).

The size of the grain is very small, 2 millimeters and downwards. Inside of this are lava bombs prolific. Especially the red lava and black lava seems to have produced a lot of lava bombs during eruptions. The grey translucent lava and the forsterite seems to have produced significantly less lava bombs.

The lavas point to a totally atypical form of eruption for the Grimsvötn line. The eruptions seems to have been very explosive for the size of this volcano. Noteworthy is that Eldgigur shows no sign of being affected by ice, nor water, so all 3 of the eruptions has happened after the end of the latest ice age. Ice would have affected the shape of the volcano due to its loose lavas, and water would have weathered the olivine.

Iceland is famous for having 27 active volcanoes. This is the believed number of volcanoes that has erupted after the last ice age, and has the ability to erupt again. Clearly Eldgigur has had 3 eruptions after the last ice age, and due to the lack of weathering of the olivine, the last of them should have been during the last 2000 years, probably a lot later than that. So, I think I can safely say that Iceland just got a number 28 to worry about.

With weathering of olivine I mean that pulverized forsterite will decay from a member of the olivine family into a member of the carbomagnesian family due to magnesiums very reactive capabilities as it gets into contact with water and CO2. A centimeter thick layer of powdered forsterite will decay completely within 3 to 5 years if it is left in the open air. So, you can actually date it.


316 thoughts on “Icelands forgotten Volcanoes

    • Problem with barbecue is, the crater is part of Brennisteinsfjöll, and it is not possible to see Hekla from there. But on the other hand, it would be possible to visit on your way from the International Airport at Keflavík to the Hekla barbecue, it’s not a lot outside of the way.

      BTW: It is not the only ancient magma chamber which is accessible in Iceland. The inside of calderas are also ancient magma feeding systems, so that would eg. be Krafla caldera, Askja caldera and the a.m. Torfajökull caldera in Iceland.

      It is also possible to see the insides of volcanoes – magma sills (GeoLurking explained in a former comment why the expression “magma chamber” is perhaps not so recommendable) – on a lot of places in Iceland’s east fjords, eg. Lón is said to be part of such a one:

      Magma feeding systems also may look like these on an eroded central volcano in Reydarfjördur, East Iceland:

      • Thanks for the links – I really wasn’t being too serious about a BBQ 😉 but I did think the idea of being lowered 120 m into an empty magma chamber (or whatever) was kinda cool! Interesting plans, too, to bore a tunnel through the cone so that one day you might be able to walk through into the chamber.

        • Getting into the chamber before lunch might be good; getting out after a good lunch might prove more difficult. 😀

          • Either/or!!, just waiting for passport……………!
            Have possible other reason for not going down the vent, ie why I can’t use the underground railway… ok wimp!

          • Thinking outloud now, 14th may be better for getting back the following week – the ruddy olympics chaos we will have 👿

          • Then we decide on 14… 🙂

            Well, abseiling down a chute is something that might make most people hesitate more then once.
            So, now we just need to see if Islander, Irpsit or Jamie knows of a good sight with a view of Hekla that has a webcam (and a hotell, lodge or something close by).

          • Daft thing is, I used to fine 1000m down a coal mine for hours, something just ‘snapped’ in the head in an exhibition hall…….. 😦

          • Was there a lot of people around?
            I suffer myself of severe “market-phobia”. I can’t stand large crowds of people moving slowly around looking at crap in a conform way… Come to think about it, I hate people in big groups, and hate shopping… So perhaps I am just a rather androphobic fella… But in smaller crowds without shopping I can be downright sociable.

          • To be honest, Alan, I have every sympathy with you. As a mere stripling of 13 I was sent down a disused mine in the Caldbeck fells to get some specimens out for my mother and her mineralogist gang – I was the only one small enough to fit through the hole! Could I even contemplate that today? You must be joking – last year on our trip to Iceland my own 13-year old was off down a lava tube like the rat down the proverbial sewer, but I couldn’t bring myself to go more than about a foot inside. Petrified in the entrance and could not move a foot further.

          • @ Carl
            Are you my twin! 😀 I HATE shops/crowds – sheep ok!!
            @ ukviggen
            Sounds like the old Drygill mine – has been some bad fights down there in the past over campylite……

        • Spot on Alan! Campylite it was – I may be completely wrong about this but I’ve always been led to believe by my mother (who is, I admit, a bit dotty!) that the specimen now in the Geological Museum was one of the many I fished out that day – the stuff was literally lying everywhere. Huge vugs in the walls, bits all over the floor. This was the early 1970s – a few years later some much more organised folks went in there and opened up the shaft-cum-adit and got out some really beautiful specimens on a semi-commercial basis. Not like that when I was there – just a broken down fence around a tiny hole in the ground – and no Health & Safety in sight – I mean, sending down a small expendable boy into a mine just for some lumps of rock! The sad thing is I don’t have any of it now.

          Was it Roughten Gill that was just down the track? Have a nice specimen of native copper from there!

          • Driggeth mine is near Drygill, Red Gill is the otherside of the hill to west near Roughten Gill, with Potts Gill’s to north!!!
            I’m green if you got some good stuff!!!

          • Driggeth! That’s the one – sadly it’s 40 years ago and my memory is very shaky. I think we did Driggeth and Dry Gill one day, Red Gill and Roughten Gill the day before, and then off to Weardale via Alston – a real whistle-stop tour of some very cool places (we lived in the south) with some mad prof from King’s or Imperial and some mysterious and very serious ‘mineral-mafia’ types. … who were all very willing for ‘the young’un’ to squirm through holes and shin up quarry faces! Happy days!!

            My interest in minerals (regrettably) waned in my mid-teens – but my mother still has some of my stuff somewhere.

    • Yepp, I remember that one, and so wanna do it 🙂

      But we will still need to find a place with a cam ontop of it that is close to Hekla for the BBQ itself.
      Irpsit or Jamie, do anyone of you know of a good spot?

        • Yes, and also I guess it would be nice if we could have a hotell or lodge nearby… 🙂

          Or at least a farm with a barn 🙂

          • Ranga? I thought I knew English but…

            Well, I am used to unusual smells. One of the mighties I produced when I arrived in the Azores after sailing without a shower for 27 days from New York… The Locals shifted in colour as I walked past on my way to the nearest Hotell with a shower.

          • Why not make the BBQ in front of the Mila i Beinni Hekla Web cam? That way everybody can join in, even those who for some reason cannot travel to that beautiful Island. At the same time the view

        • This cam is VERY close to Hella Town (in town actually), but up a MILA broadcast mast. Check out Hella Town (and lodgings) on Google Earth, this cam is located just west of the Airfield. Them horses often there hanging around belong to Farm Helluvað. Been so often there I can walk around blindfolded. Beutiful view in all directions, if sky is clear. Putting own web BBQ camera might be possible, just for the day. Was to suggest the spot but, too early to know if I can be there 😉

      • @ Carl

        Well, with half a million showing up you may find you have a bit of a problem if that is really the case but at least if anyone’s car breaks down, it will come in handy!

        ; – )

    • Driggeth! That’s the one – sadly it’s 40 years ago and my memory is very shaky. I think we did Driggeth and Dry Gill one day, Red Gill and Roughten Gill the day before, and then off to Weardale via Alston – a real whistle-stop tour of some very cool places (we lived in the south) with some mad prof from King’s or Imperial and some mysterious and very serious ‘mineral-mafia’ types. … who were all very willing for ‘the young’un’ to squirm through holes and shin up quarry faces! Happy days!!

      My interest in minerals (regrettably) waned in my mid-teens – but my mother still has some of my stuff somewhere.

  1. Haven’t had chance to look properly, what happened to Salysaalda after lunch and Godabunga’s area meters?

  2. I thought everyone would be all “atwitter” as to whether Bob is still at 90 meters? The bathemetry picture is shown on “Earthquake Report” today and is courtesy of the SOS Oceanos, but I can’t find a date on it. Any comments or thoughts out there?

  3. Hi Carl and everyone, just wanted to say congratulations on passing the half million mark – it is quite an achievement and very weill deserved – I have not made any posts for sometime but I have have been avidly “lurking” every day.. Well done everyone. xx

  4. check out the video on posted at 21.57 – impressive video of what´sgoing on in El Hierro….sorry don´t have the knowledge to post direct link!

        • Not sure that I would call them flaming stones personally – you need oxygen for flames & the ROV is underwater. Glowing pyroclastic material might be a better term.

          Think we need to wait for the report from ULPGC and IEO to put it into context.

          • Ouch! I really feel for you Karen.Pain in the ear is even worse than toothache in my opinion. I have a few times had severe pain shooting through the ear every few seconds for days, that no pain killer would alleviate. I really hope it soon clears!

    • To post a link, right click on the link shown in the box at the top of your web browser and select copy. Paste it into your comment. Check you have pasted the correct link (I have been known to paste the link for this site in by accident).

      It is easier to with two tabs open on your browser.

      After you have posted your comment, check that the link works as you expect. If not, you can correct it using the reply to your comment.

    • They really worked Faial over, but left the rest of them. Odd since San Miguel in many ways is the most interesting of the islands volcanically speakin.

    • I think Faial was the focus of that chapter.

      One thing that struck me, is that the Azores is not at a triple junction.

      It is at three triple junctions.

      The Azoran plateau essentially constitutes a plate fragment at the middle of it all.

      I’ve extended the western line of the East Azores Fracture zone over to the MAR where it seems to line up with a transform fault along that system.

      Also, I don’t think that area in the green circle is a caldera unto itself… but if it were, that circle is 100 km across.

      • Yes, it remind of Iceland in that it has several tripple junctions.

        The Circle on the image might not be a true caldera, but it is definitly something if one looks closer at it on the oceanographic bathymetric maps (or google earth as a cheaper alternative). My take is that it is some kind of large subductive area, or a an impact crater. It is a bit to much looking like a caldera or an impact crater for my liking. Especially the fault lines radiating out gives me the royal heebie jeebies.

      • Poking around in Global Tectonics 3rd ed… (abbr GT3rd)

        Triple junctions have unstable and stable configurations.

        The area along the East Azores Fracture Zone is effectively a transform fault. The line coming down from Formigas to east of St Maria intersect the line of the EAFZ that runs into and becomes the Gloria Fault (GF in the plot). This constitutes a RFF (Ridge – Transform – Transform) junction.

        According to GT3rd this is stable if the two transform faults if the velocity vectors along the two transforms forms a straight line… which in this case they do. (the EAFZ part appears to be locked though)

        Over on the western end, where I have connected what ostensibly is the other end of the EAFZ system to the existing transform that is part of the MAR… the configuration is also “stable”

        To the north, where the MAR and the North Azores Fracture Zone (NAFZ) tie in, all three sections are ridge systems. This is also a stable configuration.

        What do I mean by stable? Well, stable in that the triple junction is not actively migrating up one of the fault systems. It’s relatively stable, but changes in spreading rate or nuances in the stresses from the three LARGE plates can toss that “stability” out the window. Remember, this is the junction of the Africa, North American, and Eurasian plates. They take up a lot of real estate and have a lot more pushing them around than just what is around the Azores.

        In that document, the relative motion of the Eurasian Plate and the African plate is shown as right lateral spread across the whole of the Azores Plateau. Sub-fracturing seems to have formed independent blocks that make up that area. (looks like a diagonal grid)

        Yeah.. the Azores has it’s own special thing going on… and is probably just as interesting to study as Iceland… but more difficult since most of the action in underwater.

          • I have also a vague memory of that. But regardless, there are some stonking large volcanoes there well prepared to produce VEI-6s. So we do not even need a supervolcano.

            But… I still am looking very very suspiciously at the large hole in the ocean floor…

        • Thanks Carl and Lurking. I saw the Azores dramatically one evening as the sun set behind them. A magnificent sight. I was on a banana Boat heading to Jamaica. That voyage put me off the idea of cruise holidays for life! But there were some magnificent moments. The Azores being one of them. After that there was no sign of land for eight days. The Golfito was a very small boat. No Stabilizers and chugged along….slowly. The voyage left me with a true concept of how big the Atlantic is. How those disabled servicemen managed to row across I have no idea but by Golly they had some guts!

          • Good Morning all,
            The Azores do sound interesting, on a triple(triple) junction and not so far from the MAR, they had a Surtseyan eruption there in 1959…Unfortunately a very expensive place for a holiday 😦
            Schpeakin’ of which, I’m away for 2 weeks from tomorrow it’s getting frantic,last day of work today and I’ve still got to pack etc!!) La Palma this time 😀 So I won’t have much time to hang round here. Will of course keep an eye on El Hierro (and I may still visit) so watch out for on the schpot reports x
            PS Is Birgit still around? Would you be interested in a sample from Teneguia? La Palma, erupted 1971.

          • Hi Schteve. Yes i am always around. I am absolutely addicted to this blog and would suffer severely if i would not read it every day. I am just quiet because i am no expert and did not have any news. Yes i would love to have a sample PLEASE PLEASE. Thank you that would rock.

          • Stabilizers….

            I was on a 415 foot Frigate at one time. That particular class had a horrible maintenance reputation. Each coast had three ships of that class. One on deployment, one preparing for deployment, and one tied up to the pier acting as spare parts for the two that were functioning.

            This class had fin stabilizers. After a yard period we were doing workups. (shake down etc) In relatively calm seas, they turned on the stabilizers. The rolls got worse. According to what I was told, some brilliant individual had wired in the gyro signal out of phase. After 15 minutes of lurching around, they turned them off.

            This didn’t happen on later underway times. I also understand that the Chief Engineer had a bit of his ass chewed off by the Captain.

  5. Found some more references to volcanoes related to the Siberian Traps. They are near Tura but haven’t found a map with names on it for them. This, however, puts them in or close to the West Siberian Basin – a bit far from the unique location for the charoite with canasite.

    Personally think (but note I am no expert, not even an armchair one) that a single eruptive event couldn’t have generated that volume of flood basalt but the rift systems could have done over time; e.g. the Urengoy (Ur) and Khodosey (Kh) Rifts. Maybe I am being too picky over the terminology.

  6. there is a lot of discussions going on at the moment about Bob and the seismic graph on EL HIERRO, re the graph at the time of the Japan EQ ( it was before the swarm on El Hierro) and the Mexico EA, both seem to have only minor fluctuations on it, does that mean that the ‘ normal ‘tremor is actually a lot higher, which would explain the ongoing eruption ?

    there is also a bit of drip feeding of the videos from the eruption, to who’s benefit, makes one wonder what is ‘really’ going on there or not

    • The waves from the Japan & Mexico EQs take time to travel to the Canary Islands, hence the apparent delay in recording on Canary Island.

      Both quakes showed very clearly on the stations, even CCAN. CHIE and CCAN are different types of seismometers than the others so do not appear to pick the Japan & Mexican EQs so well. But all the Canary Island stations are used to monitor Bob.

    • A small note here. We did not in any way want Judith to go away. Our intention was to limit the copy/paste that took up a lot of place and caused confusion and grief. After several warnings, we in the end decided to remove one post. She then chose to leave, something that never was our intention.

      • Thank you, Carl. I have to agree with you on the copy/paste issue and I realise that you did not intend her to leave but just wanted her to keep within the guidelines you had set out. I just hope she reads these comments and comes back.

    • I think that the shock quality would be even greater if we knew where “here” was. If it is in northern Canada or Scandinavia it is not so shocking. If it is in Spain I would be more shocked 😉

        • Good morning eswviva, I am in Vancouver BC, and we have also been having strange weather. The jet stream was taking a dip down the coast and then back up the middle of the states.

      • It’s 25C these days in Northern Canada. There is no more snow on the ground, trees are in bloom. First time in my life I see people sunbathing in bathing suits on March 21st. The metro (subway) was filled with with people in sleeveless, shorts and sandals. The seasonal high should be 4C.

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