The current swarm at Reykjanes Peninsula that has been going on since the M5.7 NW of Krysuvík on Wednesday at 10.05 declined over the last couple of days. Today it became reinvigorated with 10 earthquakes above M4.
At the same time the earthquake swarm go reinvigorated signals was detected pointing towards movement of volcanic fluids at depth. Currently there have been more than 6000 earthquakes in the swarm.
The larger earthquakes have ranged from 2km NE of Krysuvik to 2km SW of Fagradalsfjall, but todays M4 earthquakes have mainly been at Fagradalsfjall and Keilir, with the bulk at Fagradalsfjall.
A large proportion of today’s large earthquakes (M3+) have been holding steady at depths ranging from 7 to 4.5km with no discernible upwards movement. As such, no eruption is likely to be imminent. This might though change rapidly if steady upwards movement is detected.
Due to the size of the earthquakes associated with the swarm dykes can rapidly form towards the surface, and magma ascent ratios above 2km per day is possible, with even higher speeds as and if nucleation of volatiles start to set in.
Currently the IMO has not issued a bulletin concerning an upcoming eruption, but the University of Iceland’s Volcanology Department has made a risk assessment that is concurrent with what I wrote earlier today (14.48). There is also an Aviation Colour Code of Yellow in effect for Krysuvik, but I guess this is about to be amended to also include Fagradalsfjall.
It is good to remember that the current unrest is not new, I wrote about it back in 2017, so it is likely that this is a secondary emplacement (the first was very small though).
Using energy release modelling versus bedrock resilience figures it is quite easy to see that if the current earthquake swarm continues at these energy levels the rifting will become great enough to create dykes that will reach the surface.
Signs to look out for is Volcano-tectonic type earthquakes moving upwards, low frequency tremor bursts, tornillos, and onset of harmonic tremor (likely in that order). So far none of this has been seen except for VT-signals that have remained stationary at depth.
The GPS-trajectories is also showing an intrusion at depth with a hypocenter of 6km slightly NE of Fagradalsfjall, the trajectories is though based on limited datapoints so far. The intrusion is there, but the location could very well be off.
So, what would an upcoming eruption look like if it would occur? Historic data and judging from pre-historic eruptions we can expect something similar with the Krafla Fires. Episodic outbursts of mainly effusive lava fountains and lava flows.
So, if an eruption happens, do not expect something overly big (for being in Iceland), but it could still be a bloody nuisance if it is moving towards Grindavik or other populated places.
This will be updated if and when things progress.
Edit: Post updated with nicer LF earthquake signal image.
Edit 2: Added another one thousand earthquakes to the swarm.
Edit 3: New image with even more interesting coda. I will leave new pictures down here for the time being to give a progression line. This one is yet another LF, this time from KRI-station: