Eruption on Iceland's Reykjanes Peninsula 2021: activity updates

eruption site is currently calm for now, slight inflation detected

The effusive eruption at the volcano has already ended or has remained mostly calm since 18 September as lava flows have stopped.
During the eruption, instruments continued to detect a deflation over the eruption site as magma used to leave from the deep chamber and pushed its way up to the surface.
However, GNSS and InSAR instruments observed a new inflation on the Reykjanes peninsula since the end of September. This is likely reflecting a renewed magma intrusion and migration under the surface, supported also by continued deformation of the surface.
A swarm of small earthquakes occurred in late September, located in the south of Keilir area, that may be related to a new batch of magma rising inside the volcano's conduits, although no new ground deformation has been detected during this time period.
The current inflation may not be associated with a new impending eruption.
This may take years or decades what will happens next at Reykjanes peninsula.
Source: Icelandic Meteorological Office volcano activity update 19 November 2021

Fagradalsfjall volcano (Reykjanes peninsula, Iceland): lava overflowed dam and cut off another hiking trail to eruption site

After the resumption of the effusive eruption at the current site one week ago, the activity shows signs of increasing.
It proves a formation of new lava flows in the upper part of the Nátthagi valley that have continued to fill up the valley.
The effusion of lava continues at elevated discharge rate. This is most likely reflecting at higher pace of the lava that overtook the artificial dam, crossed the hiking trail and leading towards the southern ring road.
Nátthagi valley by now is largely filled with lava flows.

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Fagradalsfjall volcano (Reykjanes peninsula, Iceland): high-resolution lava flow map update

A new lava flow map of the current eruption site has been published and updated today. The map depicts a spreading field of lava that continues to advance gradually and slowly filling up the valley of Nátthagi.
The lava flows have filled up valleys of the Geldingadalir, Meradalir, Meradalur and Nátthagi since the eruption started.
The picture also shows all artificial barriers marked as red lines.

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Fagradalsfjall volcano (Reykjanes peninsula, Iceland): activity is back after 7 days of calm and illuminates sky over Grindavik

After the longest break of 7 days of apparent calm in the effusive activity, it picked up again on 11 September as a new lava flow returned to the western flank of the main crater and continues to descend into the Geldingadalir valley.
Small lava fountains are being observed in the field of lava in the Geldingadalir valley and continue to erupt.
The activity quickly intensified accompanied by a strongly rising signal of volcanic tremor indicating rapid magma flux towards the surface.

Timelapse video of the returned effusive eruption on 11 September showing illuminated sky over Grindavik (source: @ar_etsch/twitter)

new eruption night view from Grindavik… 2021.09.11./12. amazing!#timelapse from footage: Veðurstofa Ísland#massiv #eruption #icelandvolcano #lava #volcano #iceland #icelanderuption #Geldingadalir #Fagradalsfjall #Meradalir pic.twitter.com/rgDj26Ib4U

— Ar-etsch (@ar_etsch) September 12, 2021

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Fagradalsfjall volcano (Reykjanes peninsula, Iceland): eruption continues with regular pulses of lava fountains

The eruption continues in a very similar way as during the past days, with alternating pulses of lava erupting from the vent and quiet phases, at a rhythm of 12-16 hours approximately between the lava pulses.
During the active phases, the crater fills with lava and "boils" over, often forming fountains, and forms multiple lava flows on the surface.
This morning, a new lava flow made its way towards the south and then turned east, while a smaller lava flow emitted a bit further to the west continued southwards towards Natthagi valley (s. image).
The size of the cone is constantly growing although its diameter at the top has decreased. As a consequence of the smaller volume of the bowl-shaped crater, the lava fountains are rising taller.

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Activity oscillates like heartbeat from almost absence to spectacular lava overflows

The eruption continues with no signs of ending, even though it has been going through rhythmically alternating phases of very low to very high levels. Roughly every 24 hours, it changes from one to the other extreme.
When it is high, the crater is filled with a lava lake that overflows on its rims and produces spectacular flows, as can be seen in the recent video below or in the view of the webcam right now (attached); when it is low, there is usually no visible activity at the surface.
Video:

Volcanologist Þorvaldur Þórðarson explained that these lava pulses are likely caused by large gas bubbles rising through the magma in the underground feeding system, pushing the magma out of the vent onto the surface.
Since these lava surges come at very regular intervals, these large gas bubbles must rise in very orderly pattern. Nature likes such regular processes and creates order,- think of the rhythmic behavior of geysers, for example.
The gas bubbles that are responsible for the peaks of activity at Fagradalsfjall are of course orders of magnitude larger than most similar phenomena. Likely, they originate at the top of the magma source in the upper mantle at 15-17 km depth, and once large enough to overcome a critical threshold of some sorts, they start rising and pushing the magma column upwards, resulting in the surface activity seen a short time after.