Deep earthquakes in Fagradalsfjall mountain

Today (21-July-2021) few deep earthquakes took place in Fagradalsfjall mountain that is part of Krýsuvík-Trölladyngja volcano system.

This earthquake activity was not big and the largest magnitude recorded was a magnitude of Mw0,8. Most depth that appeared had a depth of 13,4km.

Earthquake activity in Fagradalsfjalli mountain shown by a red dot, orange dots and few blue dots on Reykjanes peninsula.
The earthquake activity in Fagradalsfjall mountain on Reykjanes peninsula. Copyright of this image belongs to Icelandic Met Office.

It is difficult to know what this means. What is possibly happening is that more magma is pushing up in the magma feeding that now exist where the eruption has been happening. If that is happening, it can result in new craters or fissure opening up and start erupting. At the writing of this article this earthquake activity seems to be ongoing, but at slow rate and small earthquakes only so far.

Fog continues to block view to the crater and Fagradalsfjall mountain. But harmonic tremor data shows that the Fagradalsfjall mountain eruption is currently not erupting.

Possible end of the eruption in Fagradalsfjall mountain (2-July-2021)

At the writing of this article the eruption in Fagradalsfjall mountain has possibly ended (please note that Icelandic Met Office has not officially called the end of this eruption). This is part of Krýsuvík-Trölladyngja volcano system.

Around 03:43 UTC on 2-July-2021 the crater started erupting a cloud of volcano ash. What was unclear until earlier today was that the eruption had ended in the crater. The reason for the ash cloud was the the crater was collapsing in on it self and sealing up.

Cloud of volcano ash from the crater at around 03:43 UTC.
The volcano ash cloud as it appeared on Rúv web camera during the night. Copyright of this image belongs to Rúv ohf.

The harmonic tremor has also dropped at the same time as there is no lava flowing from the crater.

Harmonic tremor on SIL station Fagradalsfjall. The lines are showing up and down pattern and in last few hours the lines drop down to background noise. Few spikes have appeared in the last few hours but unclear what they mean.
The harmonic tremor noise on SIL station Fagradalsfjall mountain. Copyright of this image belongs to Icelandic Met Office.

What happens next is unclear. It is unlikely that eruption is going to start in the crater that stopped erupting. Normally they almost never erupt again. Magma is going to find it self a new path to erupt once a pressure has build up again in the deep crust. Once the pressure is enough it is highly possible that new earthquake swarm is going to start before an new eruption happens on the Reykjanes peninsula. How long this is going to take is impossible to know for sure.

This is the last article about Fagradalsfjall until an earthquake or a new eruption starts in Fagradalsfjalli mountain.