Reykjanes surprise

Source: https://www.visir.is/g/20212093433d/ny-sprunga-ad-opnast-a-reykja-nes-skaga

The eruption in Geldingadalir seemed to be waning. The flows from the two cones were notably weaker this morning. The cracks in the back of the cones which has been emitting steam had stopped doing so. The raised lava pool in front of the cones was emptying, and earthquake activity was almost absent. Activity has gone up and down over the past week, but this was definitely a down. Even the Icelandic activist making a nuisance of themselves in front of the cameras (and not being a particularly good advertisement for the country) were largely absent. The valley was largely filled with lava but the edges were not rising very fast. Yes , the eruption was definitely in advanced middle age.

At 11:32 today UTC), weak earthquakes occurred in the area. They were only about 1 km deep. At 11:37 a stronger event happened. And suddenly, reports appeared of a new fissure which had opened. By luck, it was in view of the main camera (but behind the second one) and we had an immediate good view. The fissure is perhaps 500 meters long, is showing weak fountaining along its length, and is producing some lava. It is located 1 km northeast of the twin peaks. That puts it along the dike, and this is clearly fed by magma in the dike.

The location is on the high plateau adjacent to Geldingadalir. We have had discussions which way the lava would take out of that valley; the most likely route involved a roundabout way to get to the Meradalir valley. It was unlikely to make it at the current flow rate: it would likely solidify on the way. It turns out, the lava found a better way, underground. The new fissure is near a gully that empties into Meradalir. The lava quickly found its way into this gully (which is no more), and within hours reached the floor of the valley. It is now expanding into Meradalir, albeit out of sight of the cameras.

The map shows the approximate location of the new fissure. The accuracy is not guaranteed! (This is an updated version, which moved the fissure to the far side of the gully). (Update 2: the extended fissure is beyond the gully, as pointed out by Reykvolc. This has been added to the drawing.)

The map shows the Geldingadalir flow, as it was expected to develop. The yellow area shows what was needed to get an overflow into the next valley, with a roundabout path to the lower valley of Meradalir. The magma decided against this and choose a short-cut instead. The red line show the new fissure (it is a bit guess work and I have assumed it is perfectly aligned with the original fissure which may not be true). It shows the two gullies, and indicates the one which the lava has chosen.

What caused this new fissure? There are two possibilities. One is that the magma pathway to the twin peaks was beginning to be blocked, and that the backed-up underground flow found a new weak spot. The second possibility is that the dike was slowly closing as the magma inside was cooling and that this squeezed out the remaining liquid. To tell we need to know the composition of the new lava. It is hard to tell the viscosity when it is flowing through such a steep gully.

How will it evolve? If it behaves like a normal fissure, then the new eruption will quickly focus on one or two spots, with the rest of the fissure ending its activity. This may be happening already as most of the fountaining now comes from two or three spots at the middle of the fissure. However, there is also new fountaining activity at the end of the fissure where it approaches the gully. A southerly extension of the new fissure has opened up here in the past hours which may take over from the earlier fissure. Four cones can be recognized along the fissure, including two in the new extension. The northeastern end of the fissure has a ridge only.

https://www.facebook.com/Almannavarnir/photos/pcb.4244255905606160/4244254928939591

We already have the first time lapse of the new fissure, thanks to astropgrah99

It is guesswork whether this new fissure will become the main eruption site or that it will be a short-lived excursion. It is fun to guess though. If it continues, the fissure could extend further towards the valley, purely because that would be a shorter way to travel for the magma. It may be time for a new camera.

How about the old eruption? The activity there remains notably weak. The two cones are slowly being eaten away from the inside, with frequent minor collapses. The cones are both cracked and if the eruption continues, may collapse. The surface flows now stay close to the cones. They have build up a lava pond enclosed in levees, and every now and then a levee develops a leak and a break out happens. Much of the flow is out of sight. The flow rate is hard to judge by eye. The composition remains fairly primitive (for Reykjanes), suggesting this is magma that had collected around 15 km deep at the interface between the deep crust above and the mantle below. how long it spend in the dike is not known, but there was no indication that the magma was aging during the eruption. That would be expected if the eruption was fed purely from the dike.

Time lapses of the ‘old’ eruption thanks to Virtual

Finally, the poll we had on the duration of the eruption has given a clear winner. We had over 500 responses, from 40 different countries as far apart as Greenland and New Zealand. Regrettably, two voters had to be disqualified for submitting multiple identical responses. The electoral authorities in their respective countries have been informed. After this edit, we received the following votes (note that ‘Longer’ means longer than 5 years):

Interesting, if we look at votes from Iceland only (in the ranking of umber of voters per country, Iceland was fourth), a different picture emerges:

Are these votes from the Iceland tourist board? I guess time will tell! So far, this is a typical Icelandic fissure eruption with a dike, multiple eruption sites and some but not enormous amounts of magma. The only uncommon aspect is the lack of involvement of a central volcano. We do not expect that a central volcano will develop here: that is not the way of Reykjanes. Once this eruption is over (whenever that will be), the next eruption will occur somewhere else on the peninsula and it will firget about this fissure.

There have been suggestions a shield may develop here. That would be most unusual, but cannot be excluded. However the new fissure indicates that the eruption has not yet reached stability. Wait and see. Iceland may yet surprise us. Again.

Albert

686 thoughts on “Reykjanes surprise

  1. We have been reduced to grasping at little flames of orange every now and then due to the ice and snow on the cams. Reminds me of the deep freeze we had here in the Dallas TX area in mid February which was a 100+ year event… It will get better.. I promise.

  2. All I can say is what a difference two days make. A very spectacular scene with the white of the snow and the black of the lava flows!

  3. It seems things are dying down,but hard to read what’s going on with the eruption-am missing the lava.

  4. Activity getting weak, but that is what we saw just before the new fissures opened… 🙂

    Would not be surprised if there is a new vent in the next day or so. If it does stop I would doubt it is for more than a few weeks, not with such a high flow rate and no magma chamber to collect in.

  5. I just realized when I looked at a map of a change in the marked path to the eruption site: About 1km of the final approach to the eruption site is perfectly aligned with the eruptive fissures! If the eruption were to extend SW instead of NE, then this path would be a very dangerous place to be. The distance between the last part of this stretch and the twin cones is about the same distance as between the twin cones and fissure 2…

    Someone said in an interview that it’s difficult to anticipate where new fissures will open. No, it’s not. They will open somewhere inside a corridor, say 200m wide, that’s aligned with the fissures and stretches SW-NE following the direction of the dyke. Placing 1 km of the marked path inside this corridor might not be such a wise idea. The intrusion went further south than this, so magma is literally under the feet of tourists walking on that path.

    Now, I don’t really expect the eruption to progress SW, but if it does (big if), I hope it’s at least preceded by steaming cracks a few minutes before. Forget about any warning earthquakes. That job has already been done by the intrusion. As we have seen in the three fissures so far, the final push can be silent.

  6. A new GPS was added by the University of Iceland about 10 days ago, MERC.
    As far I can see it is located just east of where the action takes place.

    Since the eruption started most of GPS at the Reykjanes Peninsula stopped moving significantly.
    MERC reveals the final push that lead to the opening of fissure 2 on april 5th. MERC started to move south east (away from the fissure line) and had not stopped yet this morning.

    Copyright GPS plot Institute of Earth Science – University of Iceland.

    • I find it remarkable that there are few quakes take place under the eruption site, even during the push up of the magma. Most of the action takes place in the NE part of the dike, towards Keilir.

      I wonder if there was a lot of energy involved to push magma in the fissure 2 and 3. The cracks had been formed during the first eruption already, some minor blockage prevented the filling with magma.

      Map made using skjalftalisa.vedur.is, showing eartquake activity in/near the dike 5 – 8 april.

  7. https://imgur.com/p2N0hDw

    This is where I think the eruptions are likely to occur, within this area. By analogy to what has been done in Hawaii for lava flow hazard this is zone 1. The current set of vents are all actually very close to the Reykjanes fault, where the dike began, and it is interesting that the first case of extension of the eruptive fractures was towards the north, not a lot so far but noticeable. The dike first went north, only after it had reached Keilir did it stop (not sure if that is coincidental) and then another intrusion went south towards Natthagi but actually not exactly in line with the first, it is a bit more directly south. My guess is that for the forseeable future vents will erupt along the section that is trending north, maybe not in a perfect linear fashion. Vents might not erupt south of Geldingadalir for a long time yet, possibly never.

    One thing that did confuse me is that the original maps of the dike in cross section show its source well north of where the eruption is now, closer to Keilir. But the dike began at the transform fault line during the initial tectonic swarm, and that is basically right underneath Geldingadalir. The eruptions now are basically right where the dike started, right above the deep source.

      • Yes but its hard to see the outline, google earth is for some reason very hard to get a screenshot from with good quality.. 🙁

    • Perhaps it is easier for magma to get though old fault-ridden Pleistocene lava than younger historic lavas?

      • Could be the case, the hyaloclastite that Fagradalsfjall is made from is probably not as solid as cooled lava. But none of the lava above the dike is actually historical, and only a little bit on the north side of Fagradalsfjall is even Holocene, the area is all very old so I dont really think the consistency of the bedrock is that important here.

        • Think the historic / later Holocene lavas for the Reykjanes Peninsula cover all the Pleistocene stuff that is not on a hill.

    • A nice lesson about dike forming.
      https://youtu.be/tFaz0blkYfs

      Gudmundsson tells that dikes rarely form using faults as pathway. That surprised me. I would have thought faults are weak spots for pressure coming from beneath. I wonder if this eruption forms a exception. The plate movement in the area prior to the eruption is not a coincidence in my view.

    • Go to skjalftalisa.vedur.is. Enter starting date February 23, ending date February 25. Select depths from 6 to 8km. Then you see the start of the dyke right at the initial M5.6 and the progression towards Keilir the following day.

  8. Is the crack on the hill in front of the new crater (latest fissure) getting bigger? Or is it just a trick of the light?

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