Iceland's Fagradalsfjall Fires

[bjdeming]

This isn't Svartsengi related, but it is geographically close and on the same tectonic feature, the Reykjanes Ridge:



X translation:

A swarm of earthquakes began around 9pm JST on May 24th near the northern end of the Reykjanes Ridge, southwest of the Reykjanes Peninsula in Iceland, and the active state continued until 3am JST on the 25th (updates then appear to have stopped until 7am on the 25th).
● As of 3:00 JST on the 25th, the largest earthquake was a M5.1 earthquake measuring 10km at 23:21 JST on May 24th.
● Reykjanes Ridge epicenter distribution map from IMO website M-T Figure for the past 48 hours as of 3:00 JST on May 25 (18:00 UT on May 24)

RUV just did a news update (autotranslated), noting that the swarm continues, with at least 30 out of 400 temblors thus far being over M3. They report that IMO has not yet seen signs of volcanism.

AFAIK, the nearest named submarine volcanic systems are Eldey and the submerged part of the Reykjanes system (which is west of the 2021-to-present eruptions and magmatism at Fagradalsfjall and the Sundhnuk craters).

Ah, the joys of living on a mid-ocean ridge!

 

[bjdeming]

The Eldey swarm settled down, came back weakly, and has settled down again.

The IMO update today (via GT) has a nice view of the lava berms and the Blue Lagoon complex. Emphasis added.

Continuing land rise in Svartsengi-3.6.2025​

Updated June 3



Landslides and magma accumulation continue beneath Svartsengi. However, the rate of magma accumulation continues to slow steadily compared to the rate in April and the first half of May. If magma accumulation continues at a similar rate to the past few weeks, it can still be assumed that the likelihood of a magma flow or eruption will increase as the autumn progresses. Changes in the rate of landslips, and thus magma accumulation beneath Svartsengi, may, however, affect this assessment.

 

[bjdeming]

No changes -- they're still expecting eruption chances to rise in autumn, according to today's update (autotranslated), if magma continues to accumulate. Apparently inflow has slowed down in recent weeks.

Regarding the April 1st events, per GT:

Although the eruption on April 1, 2025 was by far the smallest eruption to date on the Sundhnjúk crater chain in terms of lava flow, the sequence of events was extensive. The largest part of the event consisted of a magma intrusion that traveled north and reached as far north as Keilur. The intrusion was comparable to the one that occurred on November 10, 2023, except that the magma intrusion then mostly headed south and reached under Grindavík. The event on April 1 was therefore the second largest on the Sundhnjúk crater chain, with only the intrusion on November 10, 2023 being larger.

 

[TornadoFan]

From the IMO:

• There are indication that magma has started moving underneath Svartasengi and an eruption is likely to occur within an hour or so.

 

[TornadoFan]

From the IMO:

"
Updated at 2:11

According to seismic activity and GPS measurements showing deformation in the Sundhnúk crater series, the magma chamber that is forming is expanding more to the south than to the north."

 

[TornadoFan]

Eruption just started!

 

[TornadoFan]

The eruption fissure is about 1 kilometer long, according to the IMO.

 

[TornadoFan]

 

[bjdeming]

Thankfully, IMO reports that no infrastructure appears threatened.

That's amazing, how fast it happened! Yesterday they did their regular update, noting the sill was about 2/3 full (compared to past pre-eruption volumes) and accumulation seemed to be slowing, though seismicity over the April dike had increased slightly. If things kept up, an eruption could be expected some time in the fall.

Then, just a few hours ago, badda-BING, badda-BOOM, but in a small way (thus far, anyway).

 

[bjdeming]

MBL.IS has a classic headline (autotranslated) first published an hour after seismicity picked up and about three hours before lava broke through the ground.:

 

[bjdeming]

This ongoing but much diminished eruption has been a real polluter:



As of an X tweet about an hour ago, pollution in Reykjavik is less but still noticeable.

Per other sources, conditions closer to the crater are still dangerous and masks are mandatory for responders.

I wonder how this lava chemistry compares to earlier eruptions...

 

[bjdeming]

From today's IMO update (autotranslated):

...Wind directions are variable in the country, making it difficult to predict accurately, but the Icelandic Meteorological Office's gas distribution forecast shows that SO₂ pollution is moving east today and could cover much of South and East Iceland by evening. Tomorrow, the volcanic haze is expected to spread across much of the country, covering South, East and West Iceland.




The image above shows the Icelandic Meteorological Office's eruption distribution forecast for Wednesday, July 23 at 6 a.m.

It can also be assumed that pollution from the eruption could spread to the British Isles in the coming days. The image below shows a new forecast for the distribution of sulfur dioxide (SO₂) from the eruption on the Reykjanes Peninsula. The map on the left shows the situation at 06:01 on July 22 and the map on the right shows the predicted situation at 00:00 on July 23, 2025. The forecast covers a larger area than before and shows that the pollution could spread to the British Isles...

Thankfully, this is a very small eruption, but it certainly shows the powerful effects that some Icelandic eruptions can have.

The Skafta Fires (Laki) in 1783 was a big (flood lava) eruption in the southeastern/ south central highlands near the coast, as well as a big polluter, and everything in the Northern Hemisphere north of around 30° N got hazed, sometimes very badly, sometimes lasting for months.

Things are busy right now but I'm keeping an eye out for knowledgeable discussions of:

• Why this current eruption happened
• Why its gas emission is so high

 

[bjdeming]

Okay, on looking into it, both the Southern Volcanoes group on Facebook and Dr. Thorvaldur Thordarson say that the haze is mostly from initial SO2 releases. There hasn't been much regional ventilation since then.

Thorvaldur knows a lot about this sort of thing.

It definitely is "stinky" lava, though. Thorvaldur told mbl.is (autotranslated) that more than 300,000 tonnes of SO2 have been released thus far. =8-O

 

[bjdeming]

 

[bjdeming]

It's so nice to be having an eruption in Iceland and not be worried about infrastructure, businesses, and settlements!

IMO said Friday that the eruption slowed but then stabilized.

Isak (the drone pilot) posted this about 15 hours ago:

 

[bjdeming]

Welcome to Iceland!

That's from the IMO update -- thoughtless visitors are indeed walking on fresh lava with a very thin crust.

That's so dangerous. Yes, experts have built roads on fresh lava, squeezed a sluggishly flowing lava tongue to stop it from breaching the barriers, and so forth, but need drove them; they brought a lot of expertise into things before they acted; and then, as professionals in a challenging situation, they took a few calculated risks that, thus far, have paid off.

Sightseeing is a whole 'nother thing, and while basalt is a good insulator, no one can know how thin the crust might be on their next step.

Anyway, also in the update, the sill has begun to inflate again. The current eruption keeps going. It's an interesting situation.

 

[bjdeming]

It's an intricate situation on the Reykjanes Peninsula just now.

• A volcanic system near Reykjavik that's known for strong seismicity is having some earthquakes.

• Another system seems to be inflating as well as shaking a bit. Per the update (autotranslated):

...There has been some seismic activity west of Kleifarvatn. Krýsuvík and the surrounding area are also historically known for seismic activity, but the activity in recent times is mainly related to trigger earthquakes due to the intrusions under Fagradalsfjall and Sundhnúk. Changes in land uplift and subsidence have been measured in Krýsuvík. The area has previously shown such fluctuations. A clear explanation has not yet been found and further analyses are underway. The area has previously shown such fluctuations, but now the deformation seems to be faster than before.

Experts are closely monitoring the situation. Data is being assessed daily and results are being shared as needed...

• And finally, per the same update, "Magma accumulation continues beneath Svartsengi and has now reached a similar rate to before the last eruption. There has been no seismic activity in the area since the eruption began. " (That eruption -- the surprise one -- was declared over on August 3rd.)

No one really knows what to expect next because many centuries have passed since the Peninsula was last active.

I hope this fall and winter won't be as traumatic for the Icelanders as last year's were.

 

[bjdeming]

IMO is doing its best to make a forecast. Here's the current one (autotranslated).

Excerpt via GT:

A new eruption must be expected, but uncertainty about its possible timing is considerable.​

What is important to keep in mind, however, is that if we look at the eruptions on the Sundhnúk crater series since March 2024, we can see that the amount of magma that has flowed from Svartsengi each time is quite variable, from 12 million to 31 million cubic meters. It is therefore unwise to assume that the next event will behave like the last one. It must be assumed that the last event may have been unusual in this series of eruptions that have occurred on the Sundhnúk crater series in terms of the amount of magma that had to accumulate under Svartsengi to trigger an eruption. Experience from recent events has also shown that the rate of accumulation does not need to change much for the timing of the next possible eruption to change by a few weeks. The uncertainty in the timing of the next event is therefore considerable and the current magma accumulation period may be prolonged.


The image shows magma accumulation periods at the Sundhnúk crater series since October 2023. From March 2024 until the eruption in July 2025, magma accumulation periods had been lengthening.

Monitoring and response are based on the assumption that an eruption could begin at any time.

The Icelandic Meteorological Office's modelling calculations give a certain indication of when the probability of the next event increases, but monitoring and response plans assume that an eruption could begin at any time.

If an eruption were to occur, the most likely source is between Sundhnúkur and Stóra-Skógfell. Signs that an eruption is imminent include microseismic activity and signs of a sharp change in deformation seen on , fiber optic and GPS meters as well as changes in borehole pressure. It must be assumed that the warning of an eruption will be short, as in previous events, when the warning has ranged from 20 minutes to over 4 hours.