Earthquake activity south of Keilir mountain

On Saturday 25-September-2021 an earthquake swarm started close to Keilir mountain, at the writing of this article this earthquake swarm is ongoing.

Red dots on Reykjanes peninsula show the location of an ongoing earthquake swarm that is now happening.
Earthquake swarm on the Reykjanes peninsula. Copyright of this image belongs to Icelandic Met Office.

The eruption in Fagradalsfjall mountain has been having its longest quiet period since 19-March-2021 and at the writing of this article that is ongoing situation.

This earthquake activity suggest that the eruption time period in this part of the Reykjanes peninsula is not over, even if nothing is happening at the moment.

Krýsuvík-Trölladyngja is a volcano system is currently erupting in this area.

Article updated on 29-September-2021 at 11:49 UTC. Correct date of the earthquake swarm start added to the article.

Massive lava cave opens up, results in lava flood down to Nátthagi

Yesterday (15-September-2021) around 11:10 UTC a large lava cave just south of the crater in Geldingadalir had a roof collapse in a small area or a lava breakup in the surface. This resulted in the lava flow down Geldingadalir into Nátthagi. The flow covered Geldingadalir in less than 20 minutes. After that it did reach the barrier that stops it from going into Nátthagakriki, if that happens both walking path A and B are going to get closed forever or having to be redrawn from their current locations. Lava down that path also allows the lava flow to go in the direction of Grindavík town and nearby roads.

The lava flow yesterday did go down into Nátthagi but didn’t get far into there compared with the older lava it was flowing on top of. This sudden lava flow did put people in danger and shows that the lava field is full of dangerous caves that can collapse or burst open at any time without any warning. The lava flow that started yesterday is ongoing best to my knowledge. But the view has been limited due to fog and bad weather in Fagradalsfjall mountain this evening.

One or two idiots where seen walking on the crater rim yesterday and I think this are the same people that Icelandic coast guard had to transport from Gónhóll since they where unable to get back because of the new lava flow that had happened when they where there.

The crater is now ~334 meters above sea level high. Currently the crater is now growing in height but that can change without warning.

Pictures of this new lava flow are on social media. I can’t use them because of copyright but if searched they can be found and viewed. There are also some amount of videos of this lava flow on YouTube.

Fagradalsfjall mountain is part of Krýsuvík-Trölladyngja volcano system.

Update on the Fagradalsfjall mountain eruption on 12-September-2021

This is a late and short update on the eruption in Fagradalsfjall mountain on 12-September-2021. Fagradalsfjall mountain is part of Krýsuvík-Trölladyngja volcano system.

Yesterday (11-September-2021) at around 05:00 the harmonic tremor on SIL stations around Fagradalsfjall mountain started to show an increase in harmonic tremor after a break of 8 days. It took few hours for the magma to reach the crater and lava was visible in the crater around 12:00 UTC.

Harmonic tremor chart in purple (lowest frequency), green (mid range frequency) and blue (highest frequency) that shows in the increasing harmonic tremor by rising at the end of the link up to 6000 units (not defined) at 00:38 Icelandic time.
Increasing harmonic tremor at 00:38 UTC on Fagradalsfjall mountain SIL station. Copyright of this image belongs to Icelandic Met Office.

There have been possible new vents been opening up yesterday and today in the lava field. Icelandic Met Office says that this is a lava flow under the old colder lava and is now breaking up and looking like new vents. I don’t know yet if this is accurate, but it is my early assessment that this are new vents and are going to build new crater, at least there is a possibly of crater building if the new vents stay active long enough.

If this are new craters as I suspect, then they are going to change the lava flow quickly and increase the output of the lava flow from what it was. It might soon start to flow down into Nátthagi and other locations that are nearby.

It is a big question if the cycle eruption with no activity for hours has stopped for now. If this has turned back into an eruption that goes in 24 hours a day, that is going to allow the lava field to reach a lot more distance then before.

Update on the eruption in Fagradalsfjall mountain on 19-August-2021

This is a short update on the five month eruption day in the Fagradalsfjall mountain that is part of Krýsuvík-Trölladyngja volcano system.

  • The eruption continues its strange cycle of not erupting for few hours and erupting for few hours.
  • The consequence of this type of eruption is that the lava doesn’t flow that far from the crater. It just piles up next to the crater making the structure ever higher. I am currently estimating (this is a guess and might be wrong) the crater at 200 meters high (-+ 50 meters).
  • The eruption has now been going on for five months. Holuhraun eruption in Bárðarbunga volcano in 2014 to 2015 lasted for six months.
  • At the writing of this article there are no new craters open but it doesn’t rule out that new crater might have opened but are hidden under the amount of lava that is around the main crater. As there are some extreme large caves in this lava field. Allowing for a lot of space for new crater to form and start erupting unnoticed.

There are no more updates of the eruption at the writing of this article. That might change without warning but I don’t know if that is going to happen.

Update on the eruption in Fagradalsfjall mountain on 16-August-2021

This is a short update on the eruption in Fagradalsfjall mountain that is part of Krýsuvík-Trölladyngja volcano system.

  • New crater has been confirmed in the eruption in Fagradalsfjall mountain. This crater started to form few days ago. It follows the activity in the largest crater and remains inactive during the time period when there is no activity in the large crater.
  • This new crater is going to change lava flows in the eruption and restart lava flows in the south-Meradalir and Geldingadalir.
  • Current the new crater is building up. It is on the larger crater rim and might be unstable and collapse are likely to happen.
  • Formation of new craters following the formation of this crater is likely. When and where new craters form is impossible to know in advance.
  • It is a question if this is a new phase of the eruption. I currently don’t have an answer.
  • The new crater is visible on all the web cameras.

Fog has been blocking the view of the eruption today and I expect that is going to be the case tomorrow (17-August-2021) and maybe next few days. This fog makes it difficult to see what is going in the eruption.

Update on the eruption in Fagradalsfjall mountain on 10-August-2021

This is a short update on what is going on the eruption in Fagradalsfjall mountain that is part of Krýsuvík-Trölladyngja volcano system.

  • The eruption continues as before with few hours of eruption and few hours of no activity. (This is my personal view of the situation) Each event is an active eruption as it would happen with any other volcano. The time between eruptions now is just shorter than in any volcano in Iceland. Its hours, not decades between eruption. I don’t know why this is happening like this.
  • Cracks have appeared in the viewing area hill closest to the erupting crater. Why this is happening is unclear. There are two explanations for this. The first one is that this are tension cracks because of the eruption and lava flows nearby to this hill . The second explanation is that this is deformation cracks because magma is about to start erupting in this part of the hill. Formation of new cracks was observed early on in the eruption in Fagradalsfjall mountain few days before an eruption started in that area.
  • There is now slightly less lava flowing from the crater. Current flow is up to 9m3/sec according to latest reports about the lava flow. This studies are done by Earth Science of University of Iceland and Icelandic Metrology Office.

This eruption remains small. Currently it is even smaller than Hekla volcano 2000 eruption that was the smallest eruption in Hekla in recorded history (according to the news). While the eruption remains this small the lava is not going to flow far or is going to do so slowly. Most of the lava is just going to build up next to the crater and next nearby area.

People continue to walk out in the lava and that is extremely dangerous. The lava field, where it is deep enough has large caves full of 1100C hot lava and if the roof breaks and people fall into it there is no saving anyone from this. Just break in the lava field crust allows for lava flows to break out with same deadly consequences.

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.

Update on the eruption in Fagradalsfjall on Saturday 17-July-2021

This is going to be shortest update to the eruption in Fagradalsfjall mountain that is part of Krýsuvík-Trölladyngja volcano system.

  • Since 9th July the eruption has been unstable. Between 10th July and 15th of July the eruption continued as before with pulsing activity.
  • On 15th of July at 05:00 the eruption stopped and it didn’t start again until around 10:00 on 16th of July.
  • At the writing of this article it seems that the eruption has stopped again based on the harmonic tremor.
  • The lava flows is down in Meradalir when the lava flow happens. At current rate it is going to take 1 to 4 weeks until Merdalir overflows with lava into next valley.
  • The east side of the crater has collapsed and that allows the lava flow direct flow down into Meradalir.

It is unclear why the eruption stops and starts again. One of my ideas is that the deep feeder system of the eruption is now empty and needs time to refill. The eruption stops when the feeder system is empty. The more empty it is the longer the eruption stops since it takes more time for the magma to fill up the magma chamber that seems to be there at 20km depth or more. How long this is going to go on I don’t know but I don’t think this can go on for many months or years. Current crater is at one point going to seal it self and the eruption is going to stop because of that.

Update on Fagradalsfjall mountain eruption on 9-July-2021

This is a short update on the eruption in Fagradalsfjall mountain that is part of Krýsuvík-Trölladyngja volcano system (currently, this might change in the future).

  • Since 23:00 UTC on 5-July-2021 the eruption has been on the low side and no lava has been seen leaving the crater when the fog is less dense in the eruption area. This is the longest break in the eruption activity since it started in 19-March-2021.
  • Small amounts of lava has been seen in the crater and it is speculated that it might be flowing from the crater in tubes in the lava field. This remains unconfirmed at the writing of this article.
  • Currently the eruption is not over. It is ongoing as is.

The following is a speculation on my part.

This lack of activity and amount of lava in the crater suggests that the deep system that has been feeding the eruption is for now close to being empty or is completely empty. That system of magma chambers needs time to fill up. This lack of activity is also common for this type of volcano and magma system. Since eruptions go trough a cycles of high and low activity. This might result in the eruption starting in a new fissure in next few weeks to months along with continuing in the current crater. There is also a equal chance of the eruption just continuing in the current crater once the eruption starts at full energy again. But that might be weeks until that happens.

End of speculations

Summer is fog season in Iceland when there is no strong wind and this has been a problem for monitoring the eruption on Reykjanes peninsula in recent days. This is going to continue until September or October depending on the weather pattern.

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Fagradalsfjall mountain eruption refuses to stop (2-July-2021)

In a surprise move the activity in Fagradalsfjall mountain (part of Krýsuvík-Trölladyngja volcano system) started to increase again around 16:00 UTC and around that time the first lava was seen in the crater after it had emptied it self out during the night as was mentioned in last article.

I have been following eruptions for a long time and this is the first time that I see this happen in a crater eruption. Normally when they collapse in this way the eruption is normally over. In this case the magma cleared out the rock from the collapse over few hours (it just goes down the stream with the lava) and the eruption started as the pressure did build up again in the deep magma system. Harmonic tremor has increased again since 16:00 UTC. I don’t know if it has reached its maximum yet. That is possible, but difficult to be sure.

Red hot lava from the crater flows down on Rúv web camera. Small drown is in frame of the shot.
The eruption as it appeared on Rúv web camera. Copyright of this image belongs to Rúv ohf.

It is impossible to know for sure what this eruption does next. Since this eruption seems to be breaking a lot of the normal rules that happens during an eruption.

Harmonic tremor going almost vertical up on the SIL station Fagradalsfjall.
The harmonic tremor on the SIL station Fagradalsfjall. Copyright of this image belongs to Icelandic Met Office.

Currently there is a lot of lava flowing into Nátthagi and possibly also into Geldingadalir that is already full of lava and is about to overflow at lowest points in next few days.