It is hard to remember what Iceland was like three years ago. At that time, most (or all) eruptions were in the eastern volcanic zone, from Katla (and friends) to Krafla. (Ok, one can argue about the precise borders. Grimsvotn was about to erupt. The Thorbjorn swarm had happened and an eruption at Reykjanes was seen as possible, but the peninsula had been quiet for 800 years. This was when we postponed the eruption to 2021 due to covid (cue: April 1). Iceland followed our lead and indeed in early 2021, after an impressive series of earthquakes on the Reykjanes fault, an eruption followed in the most unlikely location: Geldingadalir, a remote valley within Fagradagsfjall, where no eruptions had occurred for perhaps 30,000 years. Who would have guessed? Since that time, there have been three eruptions in three years. And we are still waiting for Grimsvotn.

The first Fagradalsfjall eruption was perfect tourism. It was in a location where no one was endangered, while still easy to reach for the watchers. This being Iceland, webcams were put up in various locations, maintained by the locals and watched around the world. Of course, this being Iceland, the locals use the cameras to display themselves and even slogans were put on view, sometimes to the watcher’s entertainment and sometimes to their annoyance. But when entertainment is provided for free, it is hard to begrudge the occasional advert! The eruption evolved through fissures, effusive cones, tall fountains visible from Reykjavik (lucky things) an finally sputtering. We learned that Icelandic eruptions can be controlled. A wall was build to deflect the lava, and indeed the lava was deflected. The same was attempted at the place where the lava began the threaten the road and farms, and immediately the eruption ended.

The power of Iceland was obvious in many ways. As Reykjanes sputtered into action. Etna was delivering unbelievable fountains, tall enough to keep even Jesper happy (perhaps not Tallis). But it stood no chance. The eyes of the world were drawn north.

It ended after some 6 months. By that time the original valley of the eruption no longer existed, and neither did the deeper valley next door nor the hill were the first lava emerged . Iceland was left with new geography and a new hill which still has a warm conduit, and we were left with happy memories.

A year later came a new eruption, an afterthought of the first. We had kind of expected that the Earth was not finished here and that at some time the magma would break through again. It happened in the northern part of the original eruption. The eruption was much less vigorous, and season II was a pleasant sight but not on par with season I. The lava field expanded a little but that was it.

For the start of Season 2, see
https://drive.google.com/file/d/1PKzvTGMTr_Iln5VijqOosRj_SiyYNQlX/view

But intrusions continued, last winter and in the spring. As before, a dike sprung up and expanded in a NNE-SSW direction. The location of the deeper magma source is not so easy to determine. The first intrusion had been further west. This being a zone with a bit of extension, there is a region some 5 kilometer wide below which magma can collect. From there, dikes can grow. Some are very deep, tens of kilometers. This go north, and can continue for 50 kilometers or more but they never reach the surface. More common are shallower dikes at 5-7 kilometers which do not go very far but quickly move up. The current intrusion was focussed further north than might be expected, with the upward growth southeast of Keilir. But it is not clear where the magma originally came from. The earthquakes and insar showed that the dike extended between Keilir and Litli Hritur, just north of Fagradalfjall.

The eruption started today at the bottom slope of Litli Hrutur, with a 900-meter fissure extending about half the distance to Keilir. As I am writing this, the lava is beginning to flow around the hill but it is not clear to me in which direction! And sadly, the eruption is too close to the cameras for a good view! I am sure that will be fixed. This is Iceland, after all. They will try to move the eruption.

What will happen next? The eruption had a sluggish start, surprising perhaps after the vigorous dike formation. But this was also the case in Season 1, and in any case the volume seems to have increased a lot as the fissure lengthened. This could develop in an event similar to series 1, lasting several months and covering a large area but well away from roads and houses. It could also be a rerun of Season 2, lasting a few weeks. The former seems more likely given the intrusion, but this is not certain.

Viewing will be harder than for Season 1, being further away from the road and requiring a longer walk. But I am sure that the coffee van will be appearing shortly at the parking area, ready for the thirsty tourists. We are in for a treat.

Location of the dike. Initial lava flow shown in blue

Albert, July 2023

And here is a reflection by Randall, taken from the comments

My own personal observations of events leading up to the fissure eruption.

1. The website https://vafri.is/quake/#close posting quakes proved invaluable this time for knowing how events were progressing. I watched the screen literally hours and began to discern patterns. Once there was like a surge and small quakes burst out over in the Krisuvik area and you could follow this surge by watching for about 1/2 hour or so. I took this to mean a magma surge. The constant activity to the NE showed that pressure was high.

2. A key comment made by Tomas Andersson about triggered quakes related to the inSar butterfly picture helped me to understand the quakes occurring on the vafri.is/quake website for the past 3 days.

3. The FAF seisometer was a good source of watching the microquakes, and I am sure that at least 3 episodes (barefuly distinguishable) of microtremors occurred. The time from 14:50 pm to 18:00 pm today (2023-July-10) on the seismo shows a slightly thicker trace. This seems to indicate that actually watching microtremors is a very difficult science even today and fissure eruptions are still hard to accurately predict

4. The strong 5.22 quake yesterday had few aftershocks, indicating (my terms) mushy ground or softened up ground by magmatic intrusion. This in hindsight was an indicator of closeness to the actual eruption.

5. There appears to have been a small microquake around 16:38 pm which slightly shook the RUV cameras on Litli-Hrutar, and I take this as the final breakthrough of the fissure. IMO dated the eruption at 16:40 and the RUV north camera showed the first smoke at 16:41:07 pm. It is really hard to catch fissure eruptions as they first begin.

6. The two flights of small birds that I saw around midnight Iceland time were interesting. Birds seem to have a foreknowledge of events, and their flight path was directly away from the region at about right angles to it (giving them the maximum distance via minimal flight time) Before the Hebgen Montana 7.3 quake of Monday August 17, 1959, the water fowl left Hebgen Lake about 2 pm in the afternoon and their absence was noted in the sheriff’s log at West Yellowstone. The quake that evening gave the reason why the waterfowl left. They came back to the lake after the 3rd aftershock on Wednesday Aug 19th or so. My dad took our family to this epicenter about 2 or 3 days later and we saw the lake filling up, and all the damage and trees disappearing into the water and it left an indelible impression upon me as an 8 year old.

7. Scientifically things have improved, we’re in a better knowledable condition that when the 1st eruption started back in 2021.

8. The hot water pouring from the borehole in Avedir (spelling) was definitely a sign of nearness of the eruption, but it was 11 km from Keilir. That is a wide area for a thermal pulse to travel. Do we know much about how much thermal energy is spread when a dike intrudes? More studies of borehole water and temps needs to be done.

9. Several people on Volcano Cafe gave fairly accurate predictions of the location of the fissure eruption, I believe Albert might have been the first to speak up. Chad gave one as did Alice, but there were others and I apologize for not mentioning you.

Finally the excitement leading up to a fissure eruption is almost addictive. It really is fun watching a volcanic event like this occur, especially when it is fissure eruptions which have not occurred for some 800 years.

These are some thoughts as I reflect back through events leading up to the fissure eruption today.

And a response to these: the hot water can easily flow 11 kilometers, so it may well have come from the region around Keilir. The underground rock insulates well but underground water can circulate and transfer heat very effectively when coming close to the magma. Gas emissions can also heat up the region. As to the birds, this was commented on below. It seems unlikely they predict eruptions, and in fact I recall tropic birds flying very close to the eruptions at Kilauea. They may be affected by earthquakes, of course, and perhaps by the SO2 emissions that can precede an eruption – Albert