Santorini/Thera

[bjdeming]

As far as I know, there isn't any impending eruption here or in the neighborhood, but a serious seismic swarm -- NOT related to intracaldera events, per monitoring experts, reportedly -- is underway.



In that image, Santorini is at 7 o'clock and the dot in the middle of its flooded caldera is the Nea Kameni islands (lava domes).

Santorini, a Decade Volcano, is alleged by some researchers to have wrecked the Minoan civilization with a big blast back in the day (though there are other interpretations, too)..

It's a headline magnet, in other words, as well as a VERY popular travel destination, and also is in a very complex geological setting. It probably should have a thread just for background, though small eruptions are not impossible, too.

I can't sum it up here but did so back in 2023, and here's the update on that blog post just now:

February 2, 2025, 11:28 p.m., Pacific: I let the Santorini Volcano slip off my radar after doing the Decade Volcano eBook but it has come into headline news again.

That seismic swarm is interesting and so is this article (Greek) by the group monitoring Santorini, which includes, per browser translation, mention also of a seismovolcanic crisis in Santorini caldera in 2024.

According to that post, the current swarm is unrelated to the intracaldera business, and that is understandable given the complexity of this area. But what’s going on?

My understanding was that nothing as major as the Minoan eruption is impending at Santorini; that the magma chamber is recharging as restless calderas do, and that the most likely eruption scenario there, if one comes, would be similar to mid-20th century activity at the Nea Kameni lava domes out in the caldera bay; and that Kolumbo, a submarine volcano a few miles off Santorini’s coast would be a likely site of eventual eruption again at some point but nothing seemed to be looming there at the moment.

I can’t work on this tonight but will try to dig into things during the week and make it a Sunday Morning Volcano post next weekend (unless events accelerate).

The 2023 blog post below is by no means definitive but it might help you get a sense of the area and fill in the background a bit.

More as things develop. For monitoring, I'm following ISMOSAV on Facebook (Greek) right now.

 

[bjdeming]

The tremors are serious enough to force closures and scare people, but according to the linked article (browser translation), no damage has been reported and geoscientists say the cause is tectonic, not volcanic:



X translation: "Crowds of people, distressed and scared, rush to board the first ship of the day that arrived at the port of Athinios in Santorini."

Extra flights have been laid on, too.

The main concern is a major earthquake and tsunami, from what I've read so far. There's no comment yet as to any effect on volcanoes Santorini and/or Kolumbo and/or any of the others in that volcanic field.

 

[bjdeming]

Just checked the news again, as well as the USGS quake catalog for the region, which looks very concerning, with a stream of 4 and 5-pointers going on.

Per the latest update here (Greek, ad heavy, but live), via GT:

The South Aegean Region is on full alert
All services of the South Aegean Region are on full alert regarding the increase in seismic phenomena in the area of Santorini and the surrounding islands. In his announcement, the regional governor, Giorgos Hadjimarkos, notes, among other things, that absolute responsibility is required from everyone, avoidance of exaggerations and strict compliance by citizens with all preventive measures and relevant instructions from the competent authorities.

In particular, Mr. Hadjimarkos emphasizes: “An unusual natural phenomenon is underway in Santorini and the surrounding area, which we are monitoring based on the assessments and analyses of expert scientists. "For our part, as the Region of South Aegean, we are assisting the work of the competent ministry and have proactively mobilized all of our own Civil Protection forces. At this time, absolute responsibility is required from everyone, avoidance of excesses and faithful compliance by citizens with all preventive measures and the relevant instructions of the competent Authorities."

This could go in the significant earthquake thread, probably, but it remains to be seen what, if any, effect this all will have on the volcanoes. I don't think anyone really knows.

Of note, I understand that there are significant differences in the seismographic appearances of tectonic quakes and those caused by magmatic fluid/magma movement. The experts are saying this is tectonic.

 

[bjdeming]

Skyline Webcams has started a closeup pan of the caldera --



Those islands out in the middle are the tops of a cluster of lava domes where volcanism has been active in relatively recent times. The caldera was formed by the Minoan eruption, and I think there have been other, older calderas that might have left traces here and there above water but are mostly submerged -- would have to look it up again.

The sunset will blind the cam, coming right through the opening in the walls but in happier times it is quite spectacular.

I see some discoloration in the water now, but it isn't that nasty yellow-brown of submarine sulfuric gas release. In fact, a boat left a trail in it, so it's likely surface accumulation of some sort.

Landslides on the walls have been reported, so it could be rock and dirt. Maybe it's human related, too -- they reportedly had everyone empty their swimming pools to take weight off the caldera walls. In addition, this series of moderately strong tremors likely has been rough on storage tanks, water mains, and sewer lines. Maybe there are leaks.

 

[bjdeming]

Everybody focuses on the caldera, of course, but if -- big "if" -- there is any volcanism as a result of these tectonic quakes, this layperson thinks it more likely to occur at submarine Kolumbo, off Santorini's northeast coast and a bit closer to the epicentral area by Anydros Island.

Wish there was a cam looking in that direction. Back in the 1600s, Kolumbo actually did rise above the sea surface (and cause damage and casualties on Santorini from tsunamis and possibly toxic gases), but after the eruption, waves eventually washed that edifice away.

Nea Kameni, in the caldera, is still in the running, though, as magma intrusions at depth occur now and then there as part of the caldera refilling.

 

[bjdeming]

At least for USGS list and the larger magnitude quakes, seven hours of quiet have passed thus far. That's the longest interval I can see since this activity picked up yesterday. This layperson hopes it means that yesterday's 5-pointers were the peak of stored energy release and that, while clusters of strong temblors might still occur, the gaps in between them will continue to lengthen, and things will ease back into background levels. Fingers crossed.

 

[gangstonc]

Santorini is one of my favorite places to visit. I’ve explored every nook and cranny of this island. I hope nothing bad happens.

 

[bjdeming]

Lucky you! It looks like some place out of a movie, in terms of the houses and towns now, but the videos of Santorini's open flanks are beautiful, too, in a wild rocky way, with the sea in the background.

So far, so good. <Layperson speculation The tectonics of this region, in a sort of "crumple zone" as the continental plates collide, are too complex for me, but from a little reading, I do understand there is a basin -- basically, a down-dropped block of crust with straight sides -- and it's occupied by Santorini, Kolumbo, and the island of Anydros, which is close to the epicenters. Boffins reportedly (Greek) just installed more seismometers out there today.

The quakes are not megathrust or thrust faulting, but overall are along fairly perpendicular planes -- "normal" in a geometric sense, like the walls of that basin.

Maybe the basin is widening a little?

Of course we worry about how quakes will affect the volcanoes, but big magmatic systems affect seismicity, too, by heating the adjacent crust so much that it's ductile rather than brittle. I'm not saying that's the case here, but it might be a factor.

Per media interviews with scientists, these quakes are on a fault that unleashed a couple of 7-pointers in 1956, six years after Nea Kameni had erupted (VEI 2).

Just a thought: Maybe the crust had cooled a bit over those years, enough to be brittle again. Now, with both Santorini and Kolumbo reportedly experiencing magma intrusions now and then, as shown by surface deformation at Nea Kameni --



-- and various submersible studies at Kolumbo, the basin's crust might be ductile here, forcing energy to be released around colder Anydros.

But these situations are very complicated, and we'll just have to wait to see what the experts say.[/layperson speculation]

 

[bjdeming]

No new quakes on the USGS list. However --

Sorry -- apparently my USGS link above isn't updating. Here is the direct link and there are ongoing strongquakes, including a 5-pointer.




X translation of this ~14-hour-old post: "Seismic activity northeast of Santorini Island, ongoing. Distribution of epicenters from NOA (National Observatory of Athens) Geodynamic Institute's data, M-T diagram within the rectangle, spacetime diagram, cross-section. It seems that the activity has moved several kilometers northeast by the 3rd day. The accuracy of the depth of the hypocenters is not well understood, but there are few shallow ones. The mechanism is basically a normal fault with northwest-southeast extension."

Depending on which source you check, somewhere between 6,000 and 9,000 people have self-evacuated from the island, which reportedly has about 17,000 permanent residents. No mandatory evac has been called yet.

Since the epicenters started northeast of the two volcanoes, it's good news that movement is away from them.

Santorini's flank, this past January:

 

[bjdeming]

Finally got some time to delve into this a bit and soon found the best presentation of volcanic/seismic hazard and uncertainty for public purposes that I've ever read -- this discussion (Greek) successfully walks the fine line between over-reassurance and over-concern.

There's also a little background for us outsiders who weren't following the rather long series of geological events here recently -- out of concern for which the powers that be were discussing establishment of a volcano observstory ON Thira (as the Santorini area also is known in Greece, from its ancient name "Thera") as well as other emergency management messures before the quake swarm began, per other articles on this site.

Of note, he mentions the possibility of a quake swarm with some 5-pointers, which is now going on. Also, per browser translation with various spellings for Kolumbo, etc. (link will be in Greek):

https://www.facebook.com/sharer.php?u=https://atlantea.news/papazachos-i-drastiriotita-stin-anydro-kei-to-ifaisteio-tis-santorinis/
https://twitter.com/intent/tweet?text=Κώστας+Παπαζάχος:+Η+δραστηριότητα+στην+Άνυδρο+και+το+ηφαίστειο+της+Σαντορίνης&url=https://atlantea.news/papazachos-i-drastiriotita-stin-anydro-kei-to-ifaisteio-tis-santorinis/&via=Atlantea
...

...Kostas Papazachou, professor of seismology at the Aristotle University of Thessaloniki and chairman of the board of directors of the Institute of Study and Monitoring of the Santorini Volcano (IBIS).


From the afternoon of 26 January we have a very intense seismic activity between Santorini and Amorgos, in the area of Anidros. This activity includes over 100 earthquakes detected by seismic networks (with magnitudes of about 1.5 and larger) and several with magnitudes close to magnitude Μ=4.0. The most powerful earthquakes, such as the one on February 1, 2025, at 15:29, with a magnitude of Μ=4.3, were strongly felt by the inhabitants and have caused widespread concern on the island. Part of this concern is because the residents (incorrectly) combine the seismic outburst with the recent announcement, a few days ago, by the General Secretariat of Civil Protection, regarding the earthquake-volcanic crisis that has been ongoing since mid-September 2024 inside the caldera.

It is logical that two phenomena that happen at the same time, have confused the inhabitants of Santorini and create a confusion, which is exacerbated by rumors, rumors, etc.


Let's try to put things right by answering a few basic questions:

1. Where is the seismic activity, in Santorini or in Columbus?

Two different phenomena are now happening in Santorini:

• We have inside the Santorini caldera a seismic activity with small earthquakes (with sizes up to ~4), mainly in the Kameni fault, from Palaia Kameni to Fira. This seismicity is due to deformation of the volcano's northern caldera, while both phenomena have been detected in time by the networks of IMPIS, which and he was the first to inform the Greek State. The phenomenon (which is still ongoing) is similar to that of 2011-2012, i.e. it is due to the same volcanic center, and is evolving like the previous one, i.e. relatively slowly (over several months).
• In the area of Anidros we have one intense seismic sequence, which began on the afternoon of January 26, 2025 and continues until and including the time this article was written (February 1, 2025, 8:00 PM). This sequence is in the faults of the Anhydros basin, although the uncertainties do not allow us to say exactly which (or which) faults they are on.

2. Can we have two phenomena together in progress? It's a coincidence?

The reality is that we don't know exactly. We know that the same forces that cause active tectonics (faults) are also related to volcanic centers. But even if there is some distant connection, practically the two phenomena are independent in their evolution, one volcanic (in the caldera) and the other tectonic (in Anhydrous).

3. In the last few days I haven't seen any earthquakes in the caldera. Has the distortion in the caldera space stopped?

After the most powerful earthquake of January 25, 2025 (Μ=3.8) inside the caldera, we have a recession in seismicity. Although we're not sure, it is possible that this reduction in seismicity is transient, as happened in 2011-2012 in the months of July-September. The main reason is that the other quantities we monitor (distortion, temperatures, etc.) have not clearly changed.

4. Does the seismicity in Anhydros show that the Columbus volcano has also woken up?

From the available data it appears that the seismicity that Santorini has been experiencing in recent days is not in Kolumbo, but more northeast, in the faults of the Anhydros basin. The typical seismicity commonly observed at Columbo is very different, being limited to a vertical “tube” with a diameter of at most 5 kilometers, from epicenters below the volcano (at depths of about 5-10 kilometers). The seismic activity experienced by Santorini occurs further from the Columbus volcano (towards Anhydros), traces a clear tectonic fault zone with a northeast-southwest direction and has all the characteristics of a typical, intense seismotectonic activity. At the same time, the available geological data show that the two volcanic centers (Santorini and Columbo) are very different, with different microseismicity, temperatures, etc. Although information is very limited about Columbo, there is no evidence of simultaneous activation of the two volcanic centers...

Reading the whole thing is very helpful in understanding what's going on.

 

[bjdeming]

The quakes continue. The BBC reported a few hours ago that 11,000 people have now left the island.

And:


X translation: “The earthquakes northeast of Santorini are still quite large. Here are the epicenter distributions since February, the M-T diagram within the rectangle from January 26, and the space-time distribution diagram. Based on the hypocenter data from NOA Geodynamics Research. It’s become clear that the hypocentral region is moving northeast in a zigzag pattern.”

Hypocenter is where the earth actually moves; epicenter is the point on the ground surface above the hypocenter.

Northeast is away from Santorini and Kolumbo volcanoes. As this layperson understands the geography there, per sources below, going SW to NE is a basin — a dropped down area in the crust, and a very common geological formation in tectonically active areas — occupied by, respectively, Santorini volcano, Kolumbo volcano, and the Anhydros/Amorgos island area where the quakes are occurring.

To put the amount of energy being released over days in this swarm into perspective, recall the several hours of similar magnitude quakes in Iceland’s Reykjanes Peninsula near Thorbjorn on November 10, 2023, when a plate boundary separated.

This swarm’s energy release is just amazing.

Sources:

Lagios, E.; Sakkas, V.; Novali, F.; Bellotti, F.; and others. 2013. SqueeSAR™ and GPS ground deformation monitoring of Santorini Volcano (1992–2012): Tectonic implications. Tectonophysics, 594, 38-59.

Preine, J.; Hübscher, C.; Karstens, J.; and Nomikou, P. 2022. Volcano‐Tectonic Evolution of the Christiana‐Santorini‐Kolumbo Rift Zone. Tectonics, 41(11), e2022TC007524.

---

 

[bjdeming]

From yesterday through now, fewer quakes have been showing up on the USGS live list, but they are still strong, with one 5-pointer.

Dr. Papazachou said in an interview that they're still observing this unusual swarm. In his opinion, there could be a bigger quake but in the M6 range; also, he thinks it unlikely that the swarm will trigger an eruption at Santorini.

Greece announced yesterday that they're extending the state of emergency to March 3rd.

Also, INGV did an in-depth blog post on the swarm (Italian). It's a little technical but has a lot of interesting stuff in it for geonerds. (Yes, that basin is extending and subsiding, but other things are going on as well.)

 

[bjdeming]

Still about the same number on the USGS, and about the same intensity, too, but as noted here:

 

[bjdeming]

Was just working through the transfer of my Santorini chapter to Patreon and watched this again.

People who don't know the beauty of this place will be missing out big time, if they let the earthquake swarm news keep them away:

 

[bjdeming]

The swarm continues, with quite a few strong quakes yesterday but none showing on the USGS live list overnight. Reportedly, Greece has now declared a state of emergency on Amorgos Island, too.

Someone did a visualization of the quakes and public responses in the region:

 

[TornadoFan]

Something changed at Santorini. There's now a continuous tremor.

 

[bjdeming]

Do you have a link for that webicorder?

Here is an update from five hours ago:



X translation: "Santorini Island SANT observation point's record for UTC 15th, up until 01:40 just now. The seismometer is an STS-2, and it seems to be a monitor record with a filter equivalent to WWSSN's short-period seismometer applied. There are still many earthquakes."

Those look like rock-breaking quakes to this layperson, FWIW. However, there is this thread (Spanish), and overall it sounds as though something complex might now be going on at Santorini (miles away from the Amorgos swarm and a seismotectonic event that has been ongoing since 2024).

Will try to track down some official word on it.

 

[bjdeming]

One more, from two hours ago --



X translation: "Earthquake in the northeast of Santorini, according to NOA's data, the distribution of epicenters since 15th (UTC) and the SANT monitor records of the 15th, from the NOA website.https://t.co/zuL8TfXehKThe red circles on the map are observation points. Those marked as "portable" are included, but although their waveforms are not displayed, I believe they are used for determining the epicenter."

 

[bjdeming]

It's like diving into a black hole, trying to get updates on Santorini, at least in English. The Global Volcanism Program page has none; ISMOSAV shows no news; a Google news search in English and in Greek (via Atlantea) shows nothing.

Here's the webicorder on Nea Kameni, one of the lava domes out in Santorini bay; it last erupted in 1950.

As mentioned, that looks to me like rock breaking as magmatic fluids move. I can say nothing about the depth or direction. You do sometimes see this type of pattern before an eruption, and other times, no eruption occurs.

Until something official comes down the Intertubes, this rank amateur guesses that we might be seeing a lead-up to an eruption along the lines of 1950 in the caldera -- or not.

The thing to keep in mind is that this is part of a seismic/volcanic process ongoing since 2024 that is separate from the unusually strong and long-lasting swarm northeast of Santorini, around Amorgos and Anidros (? sp) islands, which started in January and by all reports involves tectonic basin extension.

Granted, it's all going on in the same basin, but that's location only, not destiny in such a big topographic feature. It is a complicated business, though, and that plus being at the focus of world attention to every official word must be tough, too.

Perhaps the boffins are still trying to figure it out before they speak.

In the meantime, well, everyone knows the Kameni Islands might erupt again some time, and if that's what's going on, now is a better time for it than during the tourist season.

If there is an eruption, Toulouse VAAC will issue an advisory, and a heat signature might light up on MODIS. Here's the Volcano Discovery page. Also, the THERA webicorder.

PS: It's very confusing but nonetheless true that most news searches bring up stories that don't make a distinction between the two ongoing geologic processes. They've got "earthquakes" and "Santorini" alright but seem to have difficulties getting into the subheadings "volcanic" and "tectonic." I check Atlantea first for news, though if you know of others pass them along please, but even that hasn't yet mentioned the seismographic change.

 

[bjdeming]

No news updates, and there seem to be fewer of those "rock-breaking" quakes (if that's what they are) in the last hour or so on the Nea Kameni webicorder.

I have found a useful in-depth site that discusses Santorini among other things (it's the same one that made that visualization of quakes and public responses above).

They describe themselves as a Paris-based group of independent scientists -- haven't checked out the details but they appear to walk that talk on their website. (The website is hard for me to access by mobile.)

They addressed the brief episode of tremor earlier yesterday:




Also, in one of the documents on Santorini available for download on the website they estimate a magma volume of ~6.5 million cubic meters under the caldera,, about 4.5 km down, with possibly a dike intrusion of perhaps 3 million cu m occurring in January and early February this year.

This they worked out through observations of the caldera wall/Nea Kameni ground deformation, etc.

For comparison, the Icelandic Met Office estimates of pre-eruption magma volume under Svartsengi range from 13 to 15 million cu m or more each time -- and the Reykjanes eruptions are considered small compared to what Iceland's "big guns" produce.

This does not sound like a major eruption is looming at Santorini, whatever else is going on over at Amorgos/Anidros. And I've found absolutely nothing about Kolumbo, in between the two.

It may change, but we'll just have to wait and see. I wish someone would release an official update!