Big basalt blasts II. Taal

In my last post I introduced the model for a new eruption mechanism/style. I will be referring to these events as big basalt blasts, this is just the silly preliminary name, not its definitive one I hope.

So how did it work? I will briefly summarize. First a magma reservoir drains through a lateral eruption or intrusion, lowering magmatic pressure allows improved contact between magma and water heating up the hydrothermal system through convection to very high temperatures, if the hydrothermal system is at the surface shallow steam explosions happen and finally one of these explosions can uncork the superheated water at depth flashing into steam in a large blast. In the heights of the phreatoplinian eruption some juvenile basaltic magma gets incorporated into the explosion, but often very minor amounts.

I have been able to confirm 3 such events since 1900, in the last post I talked about 2. The third event was actually the one that made me realize there was an eruption mechanism that didn’t seem to be well understood, this is the one this post will be about.

It was produced by a volcano that inspires deep respect to the volcanic community, a volcano in the Philippine island of Luzon. This is the story of how Taal gained much of its terrifying reputation and the aforementioned model is going to help us see beyond the surface to what was happening in the belly of the beast.


King of basalt calderas, its collapse is 24 x 15 km by far the largest of any basaltic volcano, and it is similar to those produced by upper end VEI 7 eruptions. The depression is filled by Taal Lake, formerly known as Lake Bongbong, the name by which the volcano was also called, though the true original name of the volcano was Polo. The central part of the volcano forms a square island in the lake, known as Volcano Island, with 4 short rift zones roughly perpendicular to each other. It rises to only 300 m high which is lower than some of the surrounding land. Its summit hosts the Main Crater of Taal, in the past often a spectacular display of hydrothermal activity and coloured lakes.

Barely anything is known about its history. Taal was first born as a silicic system, age unknown. By 5000 years ago it was already erupting basaltic andesite and basalt, and it seems to have been that way ever since. Many volcanoes start as silicic and then become more primitive, mafic. This may seem counterintuitive, the reason probably is that the volcano receives a high supply of primitive magma that cannot evolve as fast as it gets it. The result is that the evolved magma is gradually flushed out until not much is left.

Taal is Located within the Macolod Corridor, which is a rift related to rollback of the Manila Trench. As the trench retreats away from Luzon it creates a stretching of the island accommodated by the corridor. Rifts undergo riftings, and these need magma to fill the new space, usually provided by a volcano, this volcano here being the monster of the lake.

There are 2 ways Taal can send magma into the Macolod Corridor, to the southwest, where it can rift about 15 km away from the volcano, and to the northeast, where it can rift 70 km or more. Taal rifted to the southwest in January this year and in 1911, you will see that both events are remarkably similar except on how they ended. This is the account of 1911, a disaster from which much can be learned for the future.

Back to 1911

It all started the night of January 27, at about the same hour earthquakes start to be registered at Manila and a huge column of smoke rises from Taal. This is probably an initial intrusion below the summit (Main Crater) of the volcano. Earthquakes rapidly start to ramp up in frequency and intensity, the intrusion has started to propagate laterally to the southwest, beneath the valley of Pansipit River. Many earthquakes are felt in Manila over the following days.

This is a dyke intrusion, a small rifting you might say. How do we know? Well, first a line of fractures formed running down away from Taal, the 2 largest fractures are the faults facing each other at the sides of Pansipit River while the block in between dropped in places up to 3 meters into a graben. Where the graben meets the coast the sea invaded inland. The southwestern coast of Lake Taal rose significantly above the lake, this is the typical pattern of dyke deformation, a central graben surrounded by an area of uplift. A sword-like body of magma inflates pushing the sides outward and upward, the land right above is stretched and drops down.

Dyke-induced faulting at Lemery, southwest of Taal

More evidence is the subsidence of Volcano Island, by the time the events were over the entire island had subsided between 1 and 3 meters. There may not have been interferograms back then but with attentive observation and the knowledge required it is easy to see what was happening. The reservoir of Taal was draining into a dyke. Volcano Island was sinking as magma pressure below decreased. There is no other explanation for this subsidence because as we will see the later eruption was relatively small and ejected mostly lithics.

Submerged trees at Volcano Island due to subsidence above a deflating reservoir.

Let’s use the model shall we? We have a deflating reservoir, pressure lowers allowing contact between water and magma, this heats up the hydrothermal system, so how was this going? The morning of January 29 a group of explorers and excursionists climbs to the Main Crater where they watch explosions of mud and rocks. They had decided to stay overnight but noticed the increasing earthquakes and growing explosions so they withdrew back to the shore, wise choice. Sadly many were not as cautious.

The group of explorers journeys towards Volcano Island the morning of the 29th. The hydrothermal system is heating up.

The hydrothermal system has become a ticking bomb, much like Fernandina on June 11. At 11 PM explosions grow much more violent, a tall plume forms stricken by lightning. At 2 AM January 30 the system uncorks in an explosion heard as far as 500 km away, people report an earthquake at that time, close to the lake it was felt like three upward blows from the ground, yet it is not visible from the records. Another phantom earthquake?

Afternoon of the 29th, the situation grows increasingly unstable, intensifying mud explosions.

A furious base surge races down and outwards, it cuts, debarks and uproots trees. It blows houses to bits. On impact with the lake it pushes a tsunami onto the shores. Almost every living being within 15 km to the west is killed. The eruption is short, just about an hour. It is not too voluminous, 0.075 km3 (it was measured freshly fallen so I doubt it’s an underestimate). It is rather small, there is barely any geologic evidence of it left behind, recent studies have failed to find any deposits of this eruption. And yet more than 1300 people are dead and the blast creates a scene of absolute destruction. The damage seems too excessive, how is this possible?

First what is a base surge? The concept was born with nuclear tests, it consists of a wall of material that is pushed outwards by the pressure of the blast and then breaks over. At Taal it was directed more to the west, the eruption vent was located near the east wall of the crater so that it probably projected the weak alluvium of the crater floor westward into a giant wave.

Blast from the base surge flattens vegetation on the mainland.

The survivors describe they heard detonations with brilliant flashes followed by a rain of mud. The mud burned on contact with the skin, in the reports I have been reading they attribute it to chemical substances and to acid. This does make sense, after all the material in the surge is described as fluid mud and it is likely to have been colder than the boiling point of water, yet the burns were much deeper than those of scalding water when inspected. A hydrothermal system can be highly acidic due to all the volcanic gasses going through and reacting, this eruption mechanism is after all a gigantic hydrothermal explosion. Much of the base surge may have been acid mud.

Taal shows us big basalt blasts are capable of producing extremely hazardous eruptions with modest volume. They represent the highest degree of water involvement there can be in a volcanic eruption so the ejected material is very muddy, often accretionary lapilli is present, base surges and high lithic content are all characteristic of these explosions. Taal also shows us that a caldera collapse is not necessary for these kind of eruptions, if the reservoir drops below a certain pressure threshold, collapse or not, a explosive events can happen. It doesn’t appear there was any collapse in 1911.

Other eruptions of Taal

This year’s eruption in January was very similar to what happened back in 1911: the River Pansipit valley dropped into a graben, Volcano Island subsided, but it didn’t culminate in a large explosion, why? There is a short interval between 1911 and 2020, maybe the space created in the rift was not enough to deflate Taal as much as needed. Other factors may have been involved but that one seems relevant.

I think that one previous historical eruption of Taal may as well be grouped as a big basalt blast, the events of 1749-1754. I said rifting events can go both ways through the Macolod Corridor, the last time it went southwest was this year, the last time it went northeast was in 1749. The eruption of 1749 formed a graben system running from the NE shore of Taal lake to Laguna de Bay at Calamba. A strong seismic swarm was also felt in the line from Taal to Talim Island and the Mountains of Antipolo, beyond Lake Bay. This suggests a dyke that may have propagated across the entire Macolod Corridor, more than 70 km long. Though with the scarce information available figuring out the exact path of the dyke may be too ambitious!

Original report of the Taal eruption in 1749.
Pologrande (Big Polo) is Volcano Island. Polonuevo (New Polo) was formed in eruptions of 1716, 1731 and 1749, and has been eroded away since, it is the 4th missing southeast corner of the island The line from Taal to Mount Macolod through Polonuevo marks this short shallow rift zone that is not of tectonic origin, one of four.
The deep long dyke of 1749 intruded at a right angle to this line and did follow the tectonic rift.

The 1749 eruption may itself have evolved into a depressurization explosion. For 3 days ashfall was so thick that people had to use lights at noon. Whether this was the case or not I think the rifting event lengthened for 5 years, this is something very common for large scale rifting events (like the Krafla Fires of Iceland). A large white plume always existed at the volcano until 1754 when an enormous and exceptional eruption took place that I find very hard to explain without some equally exceptional triggering process like rifting, a caldera collapse or depressurization-driven eruptions (a big basalt blast)..

The 1754 eruption went almost non-stop for 7 months with multiple paroxysms and times of lower activity. While there is no good volume estimate available, the event is likely to have been a VEI 5+, descriptions are quite dramatic. Fr. Buencuchillo spent the last and worst days of the eruption at a convento 17 km upwind from Taal, this is his account:

“Between 3 and 4 o’clock in the afternoon of the said 29th, it began to rain mud and ashes at Caysasay and this rain lasted three days. The most terrifying circumstance was that the whole sky was shrouded in such darkness that we could not have seen the hand placed before the face, had it not been for the sinister glare of incessant lightnings. Nor could we use artificial lights as this was extinguished by the wind and copious ashes which penetrated everywhere. All was horror during those three days, which appeared rather like murky nights and we did not occupy ourselves which anything but see to it that the natives swept off the roofs the large quantities of ashes and stones which kept accumulating upon them and threatened to bring them down upon us, burying us alive beneath their weight”

Predicting the catastrophe

This series has looked closely into 3 eruptions belonging to the same eruption style, all of them had clear signs of an increasingly unstable hydrothermal system, yet in 2 of them people did not evacuate, the other situation was just lucky for the volcano was in an uninhabited area.

So I find it necessary to write here what signs should someone look for that might indicate an eruption of these characteristics brewing. It can take place in ANY volcano either silicic or basaltic or bimodal where a dyke intrusion or flank eruption is taking place that reduces significantly the pressure of the magma reservoir. It is more common in basaltic systems and it is one of the main ways that can turn them from gentle red to killer grey volcanoes, but nothing impedes their silica-rich brothers from partaking, only that in their case a lot of fresh magma is going to get involved in the eruption (so not exactly the same eruption style).

The hydrothermal system needs to be close to the surface but knowing whether this is or isn’t the case may not always be possible. I think the red flag should be increased steaming, mud explosions, any sign of hydrothermal unrest. The activity will probably ramp up over time. By the time this is confirmed the eruption may not be too far off so its best to understand well the situation before the red flag shows up, know your volcano and your hydrothermal system, look for dyke intrusions and their volume, be constantly alert for the tiniest puff of steam the volcano might throw and then catastrophe may be avoided. Or well, at least the human lives part, you can’t move a city after all, you can’t move Man… Oops I won’t spoil the next article.

Next post we are looking at potential candidates to repeat the story and going into the worst nightmares of destruction.

Relevant links

On the eruption of 1911, with photographs of the time as well as summaries of Taal historic activity:

More on the events of 1749-1754 (Spanish):


91 thoughts on “Big basalt blasts II. Taal

  1. Part 2 is even more striking than Part 1 – and that was a hard act to follow! This is really fascinating and deeply researched. Thank you, Hector!

    • I agree. Linking it to such a famous volcano brings it home.

  2. This is the most exciting series in a long time (which is big praise – I enjoy most articles here). Very thoughtful, and the mechanism explained makes too much sense to not be true. In my eyes the classic picture of a magma chamber is described too simple. There is no such thing as a roof – instead the difference between fluid and compact stone is blurred and not easy to set at a certain depth. There are “dykes” both ways, up and down. The current episode at Taal is probably the most common type of refill event for big caldera volcanos. Obviously there was quite a lot of magma involved, but hardly anything erupted so far.

    Still feels like something is missing in the picture for big basalt calderas like Taal.. Assuming there are many refill events like the current one, at some point the magma has to leave the volcano somehow (assume the current episode happens 50-100 times across the caldera, quite a bit of uplift!). Potentially it is the same mechanism as described by Hector, but on a very big scale? Something obviously needs to keep rupturing the basalt and pull it up and out?

    • I think its actually the other way around. Basalt is often very hot, especially plume basalt is usually erupted at a significant degree above its melting point which is why you get massive lava rivers. The roof of such chambers is well defined it is the bottom that seems blurry and indistinct.

      Taal seems probable to do a lot more eruptions in the next decade, it goes dormant for a few decades then erupts for a while with frequency and then repeats. Taal seems to be a good ice free analogue to Katla, except that there is no downhill gradient on the rift to allow those dikes to erupt. January eruption did involve flank vents and violent fountaining so probably a lot of that with phreatomagmatic first stage.

    • Thank you! What fills here would be the rift though, magma ends up in the Macolod Corridor where it forms dykes that cool into rock. Taal loses magma during one such draining event and the caldera subsides, like it did this year, then it re-fills slowly, currently Taal is inflating though it will take some time to reach the pre-2020 levels, maybe as much as decades.

      Another important way volcanic systems grow is by sill intrusions, new sills expand the magma reservoir laterally. Sills grow the reservoir and as the reservoir grows there is more magma to feed bigger sills, so it grows even faster…

      You are right that the magma chamber concept is too simple, this is where the reservoir concept arises, multiple chambers/sills at different depths interconnected by pipes and dykes that interact with the hydrothermal system, with areas of crystal mush and multiple melt compositions.

      • Do you think it will take decades for Taal to re-erupt? Perhaps. But now that the conduit is open, it may be easier to erupt without requiring replacing all the lost magma. I would not recommend any resettlement of Taal island. The risk is too high.

        • Yes, I think it will take decades for Taal to re-erupt, like after the 1749-1754 and 1911 volcano-tectonic events. I would consider 2020 to be the draining that ends the 1965-2020 period of Taal activity, not the start of a new period.

          But I would not recommend resettlement of Taal Island either, because some eruptions of Taal can start so fast that there is no time to evacuate even with proper monitoring. Such eruptions are unlikely to affect the mainland but can deal serious damage to the island.

          • There’s many people living in or near volcanoes around the world but living on an island 5km from shore in every direction in the middle of a massive caldera takes the biscuit a bit. Over 200,000 people live on Talim Island and the edge of Laguna Caldera as well.

        • Volcano Island is supposed to be permanent level 4 danger zone to prevent people living on it.

  3. A power station at Grímsfjall has been replaced. The old one had malfunctioned and left the monitoring equipment running with only 24h of remaining battery power. The replacement operation was visible in the GRF drumplot, as snowmobile traffic and human presence caused some strange waveforms that had us scratching our heads for a while. There is more information (in Icelandic) and some pictures from the operation here:

      • Slow inflation since June, coinciding with a period of few quakes. But no indication for any acceleration. These plots are not as usable in winter because of snow accumulation. So we may know little more until late spring – if Grimsvotn has not erupted by then.

        • Most of it is seasonal variation due to varying ice load. Look at the long term graph. It does this every year. There is also long term isostatic rebound and actual uplift. Without the isostatic rebound the up component would match the level just before the 2011 eruption and all three coordinates are back to where they were when the last eruption started…

          • Isostatic uplift related to the on-going melt of vatnajokul is indeed clear. Over the summers, that is the the dominant effect. This year the uplift is more obvious and steeper. however, that has also been the case before, e.g. in the tree years around the 2011 eruption. Weather plays a role.

      • Looks like images are not showing in some browsers. On my phone I can see all the embedded images in the comments, but in Chrome on win10 I don’t see any pictures. In Edge they are visible, so it might be a Chrome issue.

        • Its definitely a problem with chrome, doesnt work on my desktop either which I use chrome. Its only this one picture though which is weird.

      • The CSM curve is closely following the prediction. When it moves too fast or too slow, there is normally an adjustment period that follows. As there is now, although the current period of quietness is likely to be much shorter than the one over the summer.

  4. The last 24 hours of summit seismograms at Kilauea are abundant on LP events, some isolated that emerge slowly, others in a few groups of drumbeat. But much weaker than the LP a week ago.

    The shallow system is very quiet otherwise, with barely any inflation in the last month, however the deep storage of Kilauea southeast of the caldera seems to be building up magma. Stations OUTL, PUHI, AHUP and DEVL have uplifted much faster in the last month than ever since before 2018.

    No eruption on the horizon yet.

    • It does look quite similar to what happened in August of 1959, when inflation began that year. Following that it was steady for a month or two then steeply increased, and then the pre-eruptive stage in mid November with the big swarm and eruption. Must have been a lot of extra plumbing formed in 1959, it looks like a shallow eruption from halemaumau and a ring fault eruption combined and there was also to some extent a bypass of the shallow system entirely it seems.

      Probably not a perfect analogy but the early inflation was probably like now, south caldera chamber filling, but when it increased is the point the magma reached the shallow system and the signal became closer to the instruments thus stronger. I had a look at those GPS stations and the recent change actually looks exponential though it isnt very clear, south caldera chamber is probably not so simple in structure as the one that drained in 2018 but it should still be possible to do a Mogi model on it, supposedly its about 20-30 km3. If it turns out to be something crazy we could have the perfect sequel to Grimsvotns next eruption, or a prequel who knows… either way 2021 is looking interesting 🙂

    • 4 m3/s, assuming this is more of less constant then this year has seen 0.1 km3 of lava erupt into the crater. If the level of the lake is about what it was in 1996 then the crater is about 300 meters deep and ~900 meters wide, 0.2 km3 in volume, so at this rate the crater will overflow in the next few years which is rather concerning given 2002 and 1977 were both well before that point.

    • Spoke too soon; Hamarinn sneaked a shallow 1.8 in as I wrote.

  5. It looks like there is a dike forming at Kilauea. The tip has reached close to Mauna Ulu.

    • Its been seismic like that for a few months now beginning in June, ive been watching closely. That dike is its upper east rift conduit which is now pressurised after refilling the 2018 drain, likely beginning in June with the increased quakes but certainly by August when the summit GPS stations begun to rise quite noticeably as pointed out in the comment above by Hector.
      Theres nothing definite but it looks to be quite close to erupting even though HVO havent changed its rating, Kilauea has long term signs and is predictable when it has an open stable vent, but it goes from 1 to 1000 in only a few minutes during major summit eruptions, something it hasnt done since before Pu’u O’o so probably few are aware of this.

      • HVO is well aware and competent. The 2018 eruption showed that. If they haven’t changed their rating, that is for good reason. I agree with Hector. Things are evolving but there is no sign of an imminent eruption.

        • It is less HVO that I was talking about and more the people living nearby, or the tourists. I know from watching all the livestreams and following everything there were a lot who had trust issues in USGS.
          It is also an unknown for HVO as much as everyone else, they have a brilliant track record but the playing field has changed a bit, its not impossible an eruption could happen unexpectedly.

          • Yes, those earthquakes happen around the UERZ conduit, some scientists have called it the connector, which I think is an adequate name since it connects the summit with the chambers and reservoirs of the East Rift Zone as far as 45 km away. It probably looks like an horizontal pipe of magma or that is at least my best guess.

            Earthquakes around the connector happen when the shallow system pressurizes, which the connector is part of, so it is a pressure gauge, seismicity has risen gradually as the volcano refilled since the 2018 eruption, hard to tell to what point will it get before an eruption.

            HVO is competent yes, and an eruption out of the blue can also happen so some eruptions will not show any signs until some hours before or even tens of minutes for some summit eruptions. No sign to indicate Kilauea is going to snap any time soon but it is not possible to know for sure either.

          • It looks as though after recovering the pressure, the shallow system has been blocked off from the supply. The shallow deformation is levelled of and beginning to reverse which looks like the system is draining to the east to reach equilibrium, while the south caldera chamber is inflating rapidly. It is my guess an eruption could happen in short order when the connection returns hence my above comment.

        • Activity at Kilauea is still within the post-2018 background state (steady earthquakes and the summit isn’t even inflating at the moment) and there is still a lot of refilling of the reservoirs to go so it is not yet primed to blow.

          Until there is a dramatic change that could be interpreted as a pre-eruption buildup (as seen at Mauna Loa) the alert level will not be raised to yellow. It had several periods of significant unrest signals (intrusions and swarms) without leading to eruption in 1980-81 (the long-term buildup to 1983).

          So even somewhat elevated signs of activity don’t necessarily mean anything of note. The volcano is still in a deflated state after all. Therefore, I would say we are still at least a year from a new eruption and there is still a decent chance that Mauna Loa will go first.

          • It doesnt have to reinflate to 2018 levels, that represents a high stand of at least 95 and possibly as long as 500 years, the fact it is already recovered a quarter of that shows significance. The amount of post eruptive inflation exceeds that of any other period in the record, 40 cm in 2 years, and that doesnt include extra magma filling in the rifts which wont show as inflation, theres probably at least 0.3 km3 of magma intruded since the eruption ended. As stated by both Hector and me, there is abrupt and considerable inflation on the outer summit GPS since August, just not in the very shallow system that the tilt reads.

            Kilauea is a different playing field than it has been historically, it is not realistic to assume it will behave exactly as it always did which is possibly what HVO is waiting for to change the alert.

          • I dont see any sort of obvious pre-eruption build up at Mauna Loa that sets it apart from Kilauea.
            The cross caldera GPS readings at Mauna Loa are rather modest compared to what Kilauea shows, the latter is only small looking because the massive 2.5 meter dip in 2018 is still on screen but the caldera has expanded by about 55 cm since fissure 8 stopped and that is accounting for south flank movement, otherwise the number would be about 75 cm. Mauna Loa cross-caldera reads 6 cm in the same time period.

            55 cm vs 6 cm is not exactly a trivial difference, its basically a factor of 10, the same as the magma supply ratio of recent decades, which suggests that ratio still holds.

            The wild card is how full the chamber of Mauna Loa actually is, if it is nearly bursting but has been that way for decades it will look static but could be set off by a tiny supply, Kilauea doesnt have that variable right now.

          • 2018 was indeed a pressure peak, but a pressure peak of the last 20-30 years no more.

            A large historical pressure peak was the 1920s when the lava lake stood about 100 meters higher (and overflowing) than in 2018, the one you mention.

            The next large peak of about the same magnitude was reached in 1974, The lava level at Mauna Ulu rose higher than the lava lake in 2018 and pressure kept increasing after Mauna Ulu went inactive and until the southwest rift intrusion.

            Another large peak but smaller was reached before the start of the Pu’u’o’o eruption judging from tiltmeters, I don’t think pressure at Kilauea was back to those levels before 2018.

            But I do agree Kilauea will probably erupt at less pressure than pre-2018 levels the next time, it is what usually happens after a large drainage. Plus there is a tendency of increasing pressure in 1790-1924, not much net change in 1924-1974, and decreasing pressure since 1975.

          • Is there a continuous tilt record from the beginning of measurement to now? I found that for the 20th century but it stops at 2000, there was considerable inflation in the 2000s and again from 2013 to 2018, would be nice to see that data side by side. I suspect 2018 would have been much higher if Pu’u O’o was not so far from the summit, the fact the lake was 250 meters above an erupting vent and still stable shows a lot of pressure existed.

          • “Two hundred years of magma transport and storage at kilauea volcano” by Wright and Klein has the best tiltmeter data that I have seen, particularly in the appendix, but sadly it does not extend to 2018. I too would like to have a continuous graph of tilting from 1956 to now and see how the 2018 fits the big picture, but as far as I know there is none published.

          • I actually have read that paper, it is one of my favorites though now a bit outdated given 6 years has happened since its end date.


            This is the one I was talking about. Following this inflation began in 2003 up to 2007 with a net of nothing after the mid 2007 intrusion. Began again in 2010 and increased in 2012 up to the 2018 eruption which totalled about 20 cm or 200 microradians on the up direction of the UWEV GPS (I dont know about the tilt, but its probably similar to that too). This was followed by 600 microradians of deflation in 2018, and subsequently 200 microradians of inflation to the present, so today it is 200 microradians lower than the value in 2011, which is probably more or less the same as the end of that line on the above graph. I guess its really hard to plot it, but I think the highest point in 2018 placed onto that graph would be at 700 microradians and a minimum of 100 microradians after the eruption, while today it would be at 300 microradians and rising, about the same as it was in the early 60s which makes some sense with an eruption in Puna just befor then as well.

            Those numbers for the last decade come from the UWEV GPS from its ‘up’ section, showing vertical movement. Its not the exact same thing as the tilt though so I dont know how good this comparison actually is. I guess probably there will be a full 1956-current year tilt record that does include all of the Pu’u O’o eruption in full one day but until then this might be the best we get.

          • A GPS does not measure microradians. That is an angle. A GPS measures distance. A tilt instrument measures angles.

          • I know, i converted the GPS imto microradiams, that conversion is what im unsure about. I think it isnt equivalent looking now.

          • There is no such conversion. You would need at least two GPS’s.

          • I guess in that case then is there a GPS record going back to at least the 90s, so they can be overlapped somewhat with that tilt.

  6. Alaska Sand Point, M 7.4 20.54 utc. Showing up in Icelandic and Hawaian drumplots.

  7. M4.9 at Reykjanes, not checked yet. Some smaller signals in de Grisuvik drumplot minutes before the big one.

    • I did often wonder this past few weeks if that place was still active or if it stopped, looks like its still going, will be interesting when it erupts eventually 🙂

      It seems we are currently in the quiet before the storm, with this and grimsvotn, hawaii, reunion, and im sure some others, that are all set to go big but just not quite yet…

      • Wonder if this Reykjavik swarm comes from a new intrusion. Looks like some wet signatures to my amateurish eyes

      • Here visible the move on 20 / 21th june this year (M5.4, 5.6 and 5.7) earthquakes at the Husavik Flatey Fault which is part of the Tjörnes Fracture Zone.

        Graph IMO

      • And the ongoing movement at the extreme west point of the peninsula, station Nylenda, starting in januari this year.

        Not long after the unrest IMO detected unusual rapid uplift in the Mt. Þhorbjorn on the peninsula. In the gps time series around this volcano three seperate periods of uplift can be recognize, the last one the longest period but less rapid. Earthquakes were not limited to the Þhorbjorn area though, they occurred in several faults which are transverse to the plate boundary under the peninsula.

        Magma flow enabled by rifting in progress (in my amateuristic view).
        Not always followed by surfacing magma. 😈

        Interesting thing is that at the two fault zones (north an south) a longer period of unrest continues. The stress is building up in the plateboundary inbetween HFF in the north and the RPR in the south.
        Where will the next snap be?

        Graph IMO

        • Wouldn’t this be a nice topic for a post? A little review of what happened at reykjanes, what is going on and what the outlook is?

      • There s a magmatic sill thats growing under Þhorbjorn. Its been growing for quite a while now. Thats why the ground is pushed up over a local arera. If this thing keeps filling for years and refills after eruptions.. then we are seeing the birth of a primitive magma chamber.

        The chambers under Kilauea, Grimsvötn and Nyiramuragira are much much larger and more spherical and open and conduited. Only long lived high supply basalt chambers becomes like that.

      • Þhorbjorn coud erupt like Krafla with fast short events.. with large row fountains feeding fast moving channels and Aa flows. Its highly likely that Grindavik gets buried in Aa lava.
        The eventual eruption will also form a group of cinder and spatter cones. The Blue Lagoon is in risk of being buried in fast moving Aa and sheet pahoehoe. I doubt the eruption will be long lived. This area erupts MORB type basalts rather than the plume basalts of the Iceland interior

        • There are lots available for new houses in a brand new neighbourhood inGrindavík if anyone is interested.

  8. Strongest Reykjanes quake in a long time!
    “3:43 today (20th of October) an earthquake of M5.6 occurred in Núpshlíðarháls, about 5 km west of the geothermal area in Seltún on the Reykjanes peninsula. The earthquake was felt widely around the country, especially the southern part of the Reykjanes peninsula and in the capital area, which is some 25 km from the epicenter. At this time over 250 aftershocks have been detected, the largest ones in the period between 15:27 and 15:32. The largest was of M4.1, other earthquakes between 3.0 and 3.8. There are no signs of volcanic unrest in the area.

    The earthquake today is the largest earthquake measured in the Reykjanes peninsula since 2003.

    “There is an active long-term process ongoing in the area and we can expect that there will be more earthquakes in the coming hours that will be felt all the way to the capital area”, says Kristín Jónsdóttir, Earthquake hazards coordinator at the Icelandic Met Office, in an interview with RÚV today.

    A great deal of earthquake activity has been ongoing in the peninsula in 2020. Earthquakes of M5 were recorded in July this year, by Fagradalsfjall, just west of where the epicenter of the M5.6 earthquake today was. Earthquake history of the Reykjanes Peninsula shows that large earthquakes have occurred in the past in connection with large earthquake swarms. Therefore, there is the possibility of large aftershocks occurring in this swarm. Largest earthquakes in the area can possibly reach M5.5-6. Those types of earthquakes can cause damages within the capital area

    • It isnt visible on Hualalai, or down in Puna, so it might be movement of the flank of Mauna Loa, Kao’iki fault system, rather than a volcanic signal, although technically Kilaueas summit is in that fault system so its complicated.

      • These are 3 strong deep Pahala tremors in 24 hours, a nice show, the following are tremor quakes (high frequency spikes in the tremor) located in the USGS catalogue:

        3rd tremor:
        2020-10-21 00:27:27 M2.3 37.2 km deep
        2020-10-21 00:22:22 M2.5 39.2 km deep

        2nd tremor:
        2020-10-20 21:16:33 M2.4 42.4 km deep
        2020-10-20 21:15:26 M2.3 40.7 km deep
        2020-10-20 21:12:24 M2 45 km deep
        2020-10-20 21:03:15 M2.3 44.8 km deep

        1st tremor:
        2020-10-20 02:58:05 M2.3 37.7 km deep
        2020-10-20 02:57:07 M1.8 39.2 km deep
        2020-10-20 02:54:20 M2 45.8 km deep
        2020-10-20 02:54:01 M2 43 km deep

        • Together with 2 weak tremors on the 19 and 20 respectively, they make 5 tremors in 48 hours. Not bad, but still small compared to many tremor bursts of early 2019.

  9. Magnitude vs depth. A pretty decent illustration of the realm of where the brittle-ductile transition region is at.

    Only using quality 99 quakes from IMOs list (depth in km).

    Assuming a gradient of 100°C/km, that yields 1500°C at around 15 km depth.

    • Thats really a furnace… and
      I do not think that Reykjanes is not that hot at fifteen kilometers depth. Perhaps around 1200 C is more correct. Iceland plume is not in Reykjanes, but the Penninsula is hotter than the odinary mar ridge spreading south of Iceland.

      • It cannot be
        1500 degrees C
        at that depth, far away from plume centra

      • 1300 C is more probable, MAR eruptions are still pretty hot even if not as hot as a plume.

    • Will also be interesting to see if and how fast the activity will. Spread further east along the Reykjanes ridge

    • The sudden rise does not show in the detailed plots and there are a few gaps with data missing. It could just be a problem with how the averaging filter handles missing data. There is nothing in any other plots that suggests something is happening, so my guess is boring.

    • The gradual increase is the rising of the lake, now slowing as it gets colder. The short-term jitter is weather.

    • I wonder what it will do next time it erupts! anyway it will be the same surtseyan – pheratoplinian activity as always.. likley longer this time with more magma avaible.

    • While unlikley, its not impossible for something like Trölladyngja to grow up in Grimsvötn during a long lived magmatic eruption. Grimsvötn haves open conduits and magma is very close to the surface now. For that to happen a long lived eruption needs to blast a conduit up.

      The next eruption in Grimsvötn may produce a surtsey Island sequence in the caldera, knowing that more magma is avaible now. Grimsvötn 2004 made a nice tephra Island in the caldera, but stopped before it became magmatic

      • The next eruption will probably begin normally, phreatomagmatic. If it breaches the surface and becomes totally subaerial it probably will initially be a high rate fire fountain eruption like most eruptions in Iceland outside glaciers are. If that vent can stay open it could become a shield immediately, but it also could become a lava geyser which is what usually happens in Hawaii before big effusive eruptions there. Shield building could be a bit later.

  10. Came across this:

    “Campaign leader Dario Tedesco — a volcanologist at the Luigi Vanvitelli University of Campania — and his colleagues found the lava lake there filling at an alarming rate, faster than ever before.

    The analysis suggests the peak hazard will arrive in 4 years, although researchers believe an earthquake could trigger a crisis earlier.

    Tedesco said he is alarmed by parallels to the 2002 eruption, which began after an earthquake opened up fissures in the southern flank of the volcano.

    The then largest lava lake in the world drained in a matter of hours, releasing low-silica, runny lava that flowed as fast as 60 km/h (37 mph), Rolan Pease noted in his report published in Science.”

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