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 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.
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.