Kilauea III. Rifts under Hawaii.

Here is the third part of my Kilauea series that was promised, a bit more delayed than I would have wished though. Many things have happened at Kilauea since the previous part. A sill intrusion took place in the Upper Southwest Rift in August, then on September 29, about a month after the sill, lava erupted inside Halema’uma’u Crater and has been filling it up ever since, meanwhile earthquakes never cease raging under Pahala, a M 6.2 earthquake took place not too far from the Pahala swarming and at similar depth in October. However what I’m here to talk is about the plumbing of Kilauea

Knowing the plumbing of a volcano is something really difficult, because we can’t see it, it is underground. The magmatic structures are invisible, or are they? Here I piece together different types of evidence and observations that helps unravel a little about how the interior of Hawaii and Kilauea is structured.

One way of knowing the plumbing is by looking at earthquakes. These happen when one block of rock slips past another. The movement of magma can cause earthquakes by applying pressure against the rock that surrounds it, known as volcano-tectonic earthquakes. There are also other types of earthquakes thought to be caused directly by the movement or the volumetric changes of magma, like long-period earthquakes and tremor.

In Hawaii the distribution of earthquakes is also related to the residual gravity anomaly. Residual gravity highlights the differences in the strength of the gravitational field depending on the location, and corrected for altitude and other factors. Anomalies in the gravitational field can be used to find underground masses of denser material. For example the volcanoes of Hawaii have a high gravity anomaly, because the interior is thought to contain heavy material, like gabbro, that has formed from solidified magma, causing the stronger gravity attraction, and revealing the internal structures.

The deep rifts under Hawaii

When the location of earthquakes occurring under Hawaii is plotted there are some interesting things that show up. Most activity seems to be concentrated in a band oriented WSW-ENE that runs across the southern flanks of Kilauea and Mauna Loa. The activity happens at two levels, 0-12 km and 30-50 km depth. Below 50 km there are very few earthquakes in Hawaii, probably the rock is too hot here to break. The band does not show in the 12-30 km range either.

In the map below, 6-10 kilometre-deep earthquakes are shown in yellow-green while those that are 36-50 km deep are shown in purple-pink. A main WSW-ENE band can be distinguished. The deeper band has the same direction but it is displaced more to the south. Another N-S band of earthquakes shows up on the southeast flank of Mauna Loa which merges with the main WSW-ENE band.

Clusters of earthquakes are also seen under the summits of Mauna Loa and Kilauea with contrasting depths. They are long-period, LP, earthquakes presumably related to gas bubble growth in magma. Mauna Loa’s LPs are centred at a depth of 45 kilometres. In contrast Kilauea’s LP activity has been identified be 5-10 kilometres deep using relocation methods, much more shallow. The main vertical conduit of Mauna Loa must be very robust and deeply rooted compared to Kilauea.

Most earthquake activity of Hawaii occurs under the southern flanks of Mauna Loa and Kilauea, adjacent to the active rift zones of these two volcanoes. Earthquakes shown are 6-10 km (green and yellow) and 36-50 km deep (purple and pink). Seismic data is from USGS, viewed in Google Earth.

The band of earthquakes is well aligned with the East Rift Zone, the ERZ, of Kilauea, and as we will see is parallel to the contour lines of residual gravity. This is why I think the earthquakes occur in front of a deep rift zone of which the East and Southwest Rifts of Kilauea are their shallow expression. The term ERZ was created to refer to the linear zone of intrusions and eruptions extending east of the volcano. Kilauea however occupies a rather central location behind the band of earthquakes, which goes both WSW and ESE from the volcano, so the term East Rift doesn’t quite work. So in order to refer to it I will be calling it the Ka’u-Puna Deep Rift.

The deep spreading of Kilauea has been well studied in the past. Magma is continuously flowing into the deep rifts under the volcano, which inflates the rift zone, and causes the south flank of the volcano to bulge seaward, it moves up, east and south. Over time the flank is contracted until can no longer resist the strain. It breaks. Then the whole flank shifts seaward by as much as meters, and at the same time subsides as it falls back to its former relaxed shape. The cycle of rift swelling and flank contraction then repeats again. That is why Hawaii is a prolific source of large earthquakes, having produced 55 Magnitude ≥ 6 earthquakes since 1823, on various faults, including those in front of the Ka’u-Puna Rift axis.

The largest earthquake was an M 7.9 in 1868. The Great Ka’u Earthquake. It is easier to understand what happened when taking into account the Ka’u-Puna Deep Rift. Shown below are 5-3 km deep earthquakes, in white, that follow the Ka’u-Puna structure, the other N-S rift is also marked in yellow, which I here call Kapapala Deep Rift. In 1868 a large dike intrusion preceded the earthquake which would. The location of the intrusion must have extended from the summit of Mauna Loa, which erupted before the earthquake, to the eruption fissure of 1868 marked in red, which erupted afterwards. The Ka’u earthquake was observed to cause a 1-2 meter subsidence of the entire coast of Hawaii Island, from Kalae in the southwest to Kapoho in the southeast. The event was disastrous. A tsunami obliterated many settlements along the southern coast of Hawaii which were never rebuilt. Still today this coast remains largely unpopulated. The death toll was 77 people.

5-3 km deep earthquakes in Hawaii. The earthquake data is from USGS and viewed in Google earth, I highlight the two earthquake alignments.

The rupture would most likely have extended all across a reverse fault in front of the Ka’u-Puna Deep Rift, from Kalae to Kapoho, relieving the strain accumulated throughout the rift flank, it was a full rupture. The 1868 intrusion occurred at the western end of the rift setting off the earthquake. The flank then slipped away. Because Kilauea is also on top of the rift its Southwest Rift Zone snapped open and erupted immediately after the slip, the summit of Kilauea drained and collapsed.

The deep rift is usually thought to extend to a depth of only 8 kilometres under the rift zones of Kilauea. However I think this could be an incorrect assumption. Looking at the earthquake distribution I find it more likely that the deep rift extends down to more than 50 kilometres and that it extends under both Kilauea and Mauna Loa. I do think that the Ka’u-Puna Deep Rift is a most important structure to Hawaiian volcanism producing most large earthquakes, it is perhaps responsible for the apparent connection between Kilauea and Mauna Loa too.

Inflation of the rifts of Kilauea has been modelled and shows that in the 1961-1982 period it averaged 0.18 km3/year, this is nearly 6 cubic meters of magma every second that end up under Kilauea! During the 1983-2018 Pu’u’o’o eruption the spreading slowed down. Nonetheless, considering that there may be further regions of magma accumulation at depth, then most of the magma supplied to Hawaii actually remains underground to make intrusions, probably dikes and sills.

The Pahala Swarm is an enigmatic clustering of earthquakes under the town of Pahala. In the past 3.5 years seismic activity has skyrocketed spectacularly in this location. Shown below are 26-38 km deep earthquakes under this area. The location of 41 km deep tremor is also marked, most Hawaii tremor events originate from that spot. The swarm has a somewhat rectangular shape and the long axis is parallel with the Ka’u Puna Rift, probably because it is caused by it. As I mentioned earlier as it gets deeper the earthquake band seems to shift southward. This could be because of two reasons. First, the rift might widen as it becomes deeper. Second, dike intrusions in the East Rift Zone are known to be inclined, they dip southwards at 80º degrees, if this slope is extrapolated then, as you go down, the East Rift Zone ends up where the deepest earthquakes are happening.

26-38 km deep earthquakes of the Pahala Swarm shown as circles. Ka’u-Puna Deep Rift is shown as the yellow line. Seimic data from USGS viewed in Google Earth.

One interesting possibility is that Kilauea is a satellite conduit of Mauna Loa. A conduit meant to feed magma along the Ka’u-Puna Deep Rift. The Pahala Swarm and the deep tremor source could be involved with this pathway. None of this however is clear, rather an interpretation of how the structure works, and it could be otherwise too.

Apart from the Ka’u-Puna Deep Rift and the Kapapala Deep Rift, there is also a third more faint linear swarm of earthquakes. It extends from the Southwest Rift Zone of Mauna Loa towards Hualalai. I will refer to it as the Ka’u-Kona Deep Rift. Large earthquakes have also occurred here, including a M 6.9 in 1951. This swarm is less active, however it is nonetheless quite dangerous since the Kona coast is heavily populated and a future large earthquake could have devastating consequences.

View of the Ka’u-Kona Deep Rift which runs under the western slope of Mauna Loa. Earthquakes shown are 6-10 km deep and data is from USGS. Plotted in Google Earth.

I find it interesting that the Southwest Rift Zone of Mauna Loa looks almost like a symmetry axis, with the Ka’u-Kona Deep Rift and Hualalai on one side, and the Ka’u-Puna Deep Rift and Kilauea on the opposite side. The residual gravity map of the island also seems to reflect this structure. The strongest positive anomalies are near the summits of the volcanoes, which is expected since there is a lot of shallow intrusive activity there, but the anomalies extend parallel to the seismic lineaments. Mauna Loa’s intrusive core is oriented mainly southward along the Kapapala Rift. Hualalai’s anomaly is offset from its summit and elongated along the Ka’u-Kona Rift. And finally Kilauea shows a strong alignment with the Ka’u Puna direction. Overall the shape of the residual gravity field over the southern half of the island is somewhat triangular, centered on the south of Mauna Loa and with three vertices marked by Hualalai, Kilauea, and by the Ka Lae Ridge, the submarine rift zone of Mauna Loa.

Map of Hawaii Island I’ve made with topography + bouguer gravity data, and highlighting the seismic lineaments.

Earthquakes 20-50 km deep under Mauna Kea. A ring shows up under its summit. Data from USGS plotted in Google Earth.

Earthquakes at 38-50 km depth under Hawaii Island. The long-period earthquakes directly under Mauna Loa are visible. Also the main seismic cluster under the south flank of Kilauea and Mauna Loa. USGS data plotted in Google Earth.

Right below, the surface rift zones of the three volcanoes are shown. Initially near the summits, shown in orange, their direction is somewhat different from the seismic lineaments, but as they extend away they align with them.

Map showing the relationship between the rift zones of the volcanoes and the earthquake lineaments, the deep rift zones. Created in Google Earth.

Another map of the earthquake lineaments.

My interpretation of the earthquakes, gravity, distribution of fissure eruption is that there is a tremendously complicated magma structure down there. Magma makes pathways along rift zones, accumulates in sills and dikes, and connects various volcanoes of the island.

This is not unique to Hawaii, the Pacific seafloor is full of ancient volcanoes many of which are tens of million of years old. There is something however that they all have in common, rifts/dyke swarms. The volcanoes can be shaped like ridges or stars, because eruptions happen along linear zones which intrusions propagate through. Hawaii is however a magnificent opportunity to see these structures live and breathe.

Ridge shaped volcanoes in the Pacific Ocean seafloor as seen in Google Earth.

Volcanoes with rift zones at 90º angles in the Pacific Ocean seafloor as seen in Google Earth.

Star shaped volcanoes in the Pacific Ocean seafloor with 3 or more radiating rift zones as seen in Google Earth.


Relevant links

Search Earthquake Catalog USGS

Kilauea monitoring map HVO

267 thoughts on “Kilauea III. Rifts under Hawaii.

  1. On the subject of this article, is it possible the unique terrain of Kilauea is a product of its deep rift being near to the surface? Mauna Loa is oriented along a rift but there is no magma storage in it, and there are radial vents, it really is like a lava shield that just kept getting taller. Kilauea instead is a caldera and an extensive area of downdropped grabens along most of its length, it has got individual shields on it but seems to struggle to reach a great height at present. It is the only Hawaiian volcano with magma filled surface rifts too.

    Seems to me Mauna Loa is basically the equivalent of what would happen if a summit lava shield at Kilauea kept going and eventually got so big it buried the rest of the volcano, to the point it began to rift itself again but with no deep connections. Kilauea today is basically a deep rift segment close enough to the surface that the crust is unable to resist its deformation.

    • So Mauna Loa is just a buried older version of Kilauea you’re saying…

      • Possibly. It actually is regardless because that is how they grow but in this context it is infering there could be stages of a Hawaiian volcano, Kilauea is possibly still only embryonic and has yet to build a tall shield, rather being a mostly underground structure at present.

        I would guess in the future Kilauea could well be a double volcano, a main summit complex above its modern caldera but possibly another satellite at the location above what we call the middle ERZ today, which seems to be its own magma storage but is not fed from below much unlike the real summit. That is the case today though, in 50,000 years the modern surface will be many km underground at those locations and the connections will be very deep and robust, like presumably is the case far under Mauna Loa. So Kilauea will possibly be a double volcano with two summits 15 km apart, or alternatively a volcano with a gigantic caldera and far greater capabilities and magma storage than Mauna Loa or even Iceland, a real flood basalt volcano. One can dream 🙂

    • Kilauea is on the slope of Mauna Loa, and these slopes creep down towards the sea. It is hard to build a good edifice if the ground underneath you is shifting. I am not sure why you think there is no magma storage in the Mauna Loa rift. There seems no good reason why there wouldn’t be magma pockets. Eruptions in Mauna Loa occur on the rift, starting from the summit, and this progresses much too fast to be tube fed.

      • Mauna Loa haves lots lots of pahoehoe that carpets its flanks. It too haves episodes of slow shield building. Most of Mauna Loa been build by long lived shield tube eruptions. Fast fissure eruptions are just the current style of activity

      • There are no pit craters or graben structures on Mauna Loa, only at its summit and a short stretch of its SWRZ (which could be considered to be within its summit boundary). I think of eruptions from Mauna Loa as being like massively scaled up versions of what Nyiragongo does, a dike moves down the rift rapidly. I think having magma in the way would serve to slow it down if anything. The same thing is seen from Kilauea, distal eruptions that are fed directly from the magma system at or near the summit (1823, 1840) have very rapid progression, high intensity, low fountaining, and form long fissures. Those that originate at a magma chamber further along the rift will often centralize to one vent (1960, 2018) or are wandering eruptions (1955), and high eruption rates take some time. Basically every eruption from Mauna Loa is of the first category, all its eruptions are dikes from the summit, where eruptions on Kilauea can happen largely separate of the summit outside of overall pressure.

        I should make it more clear I think generally Mauna Loa had asimilar structure to Kilauea at one point, low slope abgle, large caldera depression and many pits along a wide rift zone. But what is seen today looks more like a radial shield that has been fractured by continued movement of that deep rift, but the deep rift itself does not have anything to do with the eruptions on the flank. This is supported by the pre-1868 historical eruptions, which were only very loosely controlled by rift zones.

        • Mauna Loa’s original rift zone was probably the Kapapala/Ninole Hills Rift. The Ninole Hills were active up until 100,000 years ago, about the time Kilauea started growing, also about the time Hualalai shield stage ended. Kilauea is clearly blocking the Kapapala Rift which had an eastward flank movement. So most likely the inception of Kilauea forced Mauna Loa to abandon its original rift zone and develop new ones. Still though they will never work the same as Kilauea’s. Mauna Loa is buttressed on one side by Hualalai on the other by Kilauea.

          Kilauea’s rifts are young instead, and can freely push the flank into the ocean. Resulting in the hyperactive decollement fault there. Kilauea also has an overall higher magma supply. This has caused its plumbing to grow extensively across the rifts develop magma chambers, conduits far into the East Rift Zone. This also has some consequences. The big fissure eruptions of Kilauea start from small satellite magma storage far from the summit. 1955 and 1960 started from Honualua Hill, 45 km from the summit, and the summit took several days to start deflating. The connection is too long so reduces the eruption rate.

          Mauna Loa also has rift conduits and satellite magma chambers but have not developed far into the rift. Perhaps because the magma flux is not high enough, or perhaps because Mauna Loa is recovering from a recent large collapse. Magma structures are changing, being constructed and destroyed. Perhaps Mauna Loa will regrow a more extensive rift plumbing. Same as Kilauea has probably lost its extensive rift plumbing at times in the past.

  2. So I checked out the quakes on that is updated more often than the crude ones on If you Zoom in on the quakes they’re placed in lines, quite regularey. Nature does not work in that way, so is it IMO that places the quakes likte that, of some algorithm in the map service that needs tweaking?

    • It’s a consequence of using three decimals for the lattitude. With an earth radius of 6371km, 0.001 degrees corresponds to 0.001*pi/180*6371000m = 111m, which is a close match to the distance between the lines.

  3. Thinking that what we see now is a reopening of the dike from earlier in the year. The dike in March probably was forced shut except for along one path of least resistance, and now enough pressure has built to force the crack open again, except this time the crack was a little more open and lubricated by the older magma that probably was still liquid in places. I think this will happen many times in this location until the deep source runs out, which could be in a long time. Krysuvik eruptions in the 1100s erupted about 0.3 km3 of lava, so maybe 3 km3 of magma involved in the rifting episode. The dikes there were probably much longer though, slow eruptions like at Fagradalsfjall probably have much higher eruption to intrusion ratios than fissure eruptions, instead of 10% erupting it might be over 50%, possibly even closer to 90%. So Fagradalsfjall might need to be renamed to just Fagrafjall after this is all done…

  4. So, Geldingadalir averaged 11 m/s over the course of its entire eruption. It has now recharged after 3 months, suggesting that the longterm feed rate into the rift is 7-8 m/s. The Keilir earthquakes started within a couple weeks of the eruption stopping, which would tend to suggest the supply never really stopped, just the rift supply was overdrawn and so the rift/conduits shut up.

    That makes more sense as I was rather surprised at the eruption stopping. Given a typical Reykjanes eruption puts out 0.1-0.3 km^2, and they are not near as solidly sealed shut as they have a rift system that erupts every 1000 years, would seem that Geldingadalir would have to have more than that to have broken to the surface in the first place. Also, even if it has a lower feed rate than the other system, which would seem a likely reason for sealing shut, it still skipped a lot. Also because it is a fairly narrow push from the depth rather than feeding into established rift system, it would seem like it should erupt a larger share of its supply.

    • That is my thinking, there is an open conduit up to the depth of the quakes, and above that magma had to create a dike which has opened up again now that pressure is high enough. If this goes long enough to melt open a path then the dike crack closing will not stop the flow of magma and a shield might form if the conduit can stay open.

      If it is the same crack opening then an eruption will probably be on the same line, maybe not exactly the same place but close. Eventually we will end up with a line of cones across the mountain, maybe bigger fissures closer to Keilir where the elevation is lower and the distance to reach the surface could be less. The cone from last eruption would be the tallest mountain in the area if it was a km to the north, further formation of similar cones could result in substantial elevation increase at Fagradalsfjall 🙂

    Deformation from December 16 to December 22, 2021.
    Michelle Parks Image Processing.

    Updated 12/23 at 16:10 LT

    There is still a major earthquake at Fagradalsfjall, around 2000 earthquakes have been recorded since midnight, most of them near the eruption sites at Fagradalsfjall at a depth of 5-8 km.

    • And scroling through, there’s nice footage of the Hunga Tonga underwater volcano. Thanks for the Twitter link, Luis.

    • No one has made a comment about the 3 cm rise over to the right of the picture? This seems significant, as you can see some near Keilir itself.

        • The ground might be rock hard around Keilir from the Pleistocene eruption. It has probably all solidified by now and took up space, meaning the dike has to go south. Just a theory.

  6. Swarm has died down a bit now, the eruption might be very near 🙂

    • I’m noticing the steady decline, too. It may fall to background levels in a couple of days.

      I’m waiting for the Fagradals drumplot to resume the regular pulses of tremor it has been showing for months (that lined up with the pulsing of the volcano). It fell silent as this rifting episode started. My guess is the magma has taken advantage of the rifting aseismically. Now the rifting has paused, it will be interesting to see what happens if the pulses of tremor restart.

      My popcorn is getting cold…

      • The fissure dyke stopped cutting through the ground. Now it may fill up instead and it will go towards the surface Instead ?

  7. Assuming camera conditions are the same tonight as last night, the ground has heated up a bit at the Geldingadalir cone, particularly the spine to the right where new hot spots have appeared over a 24 hr period. I saw the hint of these spots last night, but they are now visible tonight. See

    Of course, this all might mean nothing at all.

      • For whatever it’s worth, I passed by the site Tuesday afternoon and was surprised to see a great deal of steam rising over the lava field in the direction of the cone as seen from the southern parking lot area. As I was driving, and as the EQs hadn’t yet started, I didn’t make any effort to pinpoint an exact location.

  8. An example of how ridiculously resilient are the Canarian Pines (Pinus Canariensis) is this video from the La Palma crater, showing tree trunks standing through the rim and into the crater.

    By the way, GPS in Cumbre Vieja shows inflation again on the south-east with deflation on the southeast, for 5 days.

  9. Very weird, FAF has died down again.
    So fireworks canceled then? =/

    • shows recent activity (timestamp 5:51 am UTC Friday 24-Dec-2021) again. Some of the trace seems to show definite magma movement (broader trace line)

      • If you’re referring to the tremor plot, a broader line does not mean magma movement, that is a common misunderstanding. Each point on that graph simply shows the minimum and maximum amplitudes of the seismometer during a measurement interval. The top value is often a quake, particularly during a swarm like this. The bottom value is the ambient noise. Usually wind waves, or human activity.

        During the eruption, the line was broad when the eruption was episodic. Then you saw both the eruption tremor and ambient noise in the graph. During periods of continuous eruption, the line was high all the time and not so broad at all.

  10. From HVO on todays volcano update.

    “New breakouts on the surface of the Halemaʻumaʻu lava lake appeared just before 8 PM last night following a resumption of strong volcanic tremor at 7:30 PM. About half an hour later, the summit began to deflate, reversing the strong inflationary episode of the prior 24 hours leading up to the return of eruptive activity.”

    Looks like the eruption is truly episodic now, like the eruption of 1967-1968, which is resembles to a great degree. Seems also that despite the similar appearence HVO is distinguishing the current deformation from a DI event.

    It might be hard if the eruption has to go through the lake, but I do hope we can get a high fountain sequence from this. It is similar to the cones that formed on Fagradalsfjall just before it started going into geyser mode.

    • Friday
      24.12.2021 15:03:22 63.881 -22.251 3.4 km 5.1 99.0 2.6 km SSE of Fagradalsfjall

  11. Friday
    24.12.2021 15:03:22 63.881 -22.251 3.4 km 5.1 99.0 2.6 km SSE of Fagradalsfjall

  12. M4.7. Strongest one so far, and shallower than before. My bet is an eruption just above Natthagi..

    • Friday
      24.12.2021 15:03:22 63.881 -22.251 3.4 km 4.7 99.0 2.6 km SSE of Fagradalsfjall

    • I agree, close to there. Wish we had the one poster who got the last location correct within 500 m. He did a fantastic job.

  13. Still not enough tremor for me… (at Fagradals…not in my hands)

  14. Lohi is rumbling. M4.9. low amplitude quakes don’t show, as no siesmo nearby.
    I’m not happy with the new HVO website design. Probably made it more phone-friendly, but like the old style mucho.

  15. I noticed that there seems to be a lot of icelandic earthquake activity showing up in areas quite a bit further away from Fagradalsfjall, some are showing up as locations like Snaefellsjökull north and south of it.

    There’s also one which is being reported as a 4.1 near Katla.

    Is this a computation error where it can’t plot the earthquakes properly due to the sheer volume of them being reported?

    Granted this was on Volcano Discovery so might be an error at their end.

    • The 4.1 was definatley a map error, it shows near Katla but when you look at the actual detail it says it’s near Fagradalsfjall. The others still say their near the other volcanoes though.

  16. Friday
    24.12.2021 18:28:19 63.888 -22.253 4.9 km 4.7 99.0 1.9 km SSE of Fagradalsfjall

  17. The first 50 quakes near Keilir ordered by depth and quality of signal. 90% is considered reliable, but we definitely have very shallow quakes now
    Ref# Day Date Time Lat Long Depth Mag Qual Location
    1519 Thursday 23.12.2021 09:11:28 63.874 -22.508 0.0 km 1 66.25 5.0 km NW of Grindavík
    1568 Thursday 23.12.2021 08:41:24 63.87 -22.277 0.1 km 1.3 99 3.6 km S of Fagradalsfjall
    1633 Thursday 23.12.2021 07:21:35 63.862 -22.276 0.1 km 1.7 99 4.5 km S of Fagradalsfjall
    691 Friday 24.12.2021 06:28:34 63.897 -22.233 0.1 km 0.5 90.01 2.1 km ESE of Fagradalsfjall
    944 Friday 24.12.2021 01:50:11 63.922 -22.217 0.1 km 1.5 90.01 3.1 km SW of Keilir
    665 Friday 24.12.2021 06:50:24 63.891 -22.248 0.2 km 1.8 90.03 1.8 km SE of Fagradalsfjall
    548 Friday 24.12.2021 11:39:24 63.907 -22.245 0.2 km 0.5 90.01 1.5 km ENE of Fagradalsfjall
    577 Friday 24.12.2021 11:05:53 63.876 -22.272 0.2 km 0.5 90.01 2.9 km S of Fagradalsfjall
    847 Friday 24.12.2021 04:48:44 63.878 -22.244 0.2 km 0.7 90.01 3.1 km SSE of Fagradalsfjall
    920 Friday 24.12.2021 03:48:10 63.882 -22.294 0.2 km 0.6 90.01 2.5 km SSW of Fagradalsfjall
    1674 Thursday 23.12.2021 06:20:47 63.9 -22.241 0.2 km 0.4 90.01 1.6 km E of Fagradalsfjall
    1102 Thursday 23.12.2021 21:10:09 63.878 -22.3 0.2 km 0.2 88.37 3.0 km SSW of Fagradalsfjall
    599 Friday 24.12.2021 09:45:07 63.917 -22.259 0.3 km 0.4 90.02 1.8 km NNE of Fagradalsfjall
    106 Friday 24.12.2021 17:06:43 63.893 -22.256 0.3 km 0.8 90.01 1.4 km SE of Fagradalsfjall
    463 Friday 24.12.2021 12:44:22 63.921 -22.204 0.3 km 0.3 90.01 2.8 km SW of Keilir
    252 Friday 24.12.2021 15:23:57 63.896 -22.243 0.3 km 2.1 77.21 1.7 km ESE of Fagradalsfjall
    1246 Thursday 23.12.2021 14:04:08 63.872 -22.275 0.4 km 1.4 90.02 3.4 km S of Fagradalsfjall
    609 Friday 24.12.2021 08:49:38 63.901 -22.237 0.4 km 0.8 90.01 1.8 km E of Fagradalsfjall
    1144 Thursday 23.12.2021 16:47:06 63.876 -22.311 0.4 km 0.6 90.01 3.4 km SSW of Fagradalsfjall
    1262 Thursday 23.12.2021 13:33:06 63.922 -22.233 0.4 km 1.2 90.01 3.0 km NE of Fagradalsfjall
    1515 Thursday 23.12.2021 09:14:31 63.864 -22.262 0.4 km 1.2 90.01 4.3 km S of Fagradalsfjall
    1672 Thursday 23.12.2021 06:23:17 63.888 -22.241 0.4 km 0.5 90.01 2.3 km SE of Fagradalsfjall
    1682 Thursday 23.12.2021 06:11:32 63.879 -22.282 0.4 km 0.5 90.01 2.6 km S of Fagradalsfjall
    2095 Wednesday 22.12.2021 22:21:34 63.898 -22.236 0.4 km 1.4 90.01 1.9 km ESE of Fagradalsfjall
    334 Friday 24.12.2021 14:31:30 63.886 -22.231 0.4 km 0.4 86.89 2.8 km SE of Fagradalsfjall
    270 Friday 24.12.2021 15:11:52 63.893 -22.254 0.5 km 1.5 90.03 1.4 km SE of Fagradalsfjall
    300 Friday 24.12.2021 14:52:41 63.892 -22.247 0.5 km 0.4 81.93 1.8 km SE of Fagradalsfjall
    94 Friday 24.12.2021 17:23:12 63.872 -22.259 0.5 km 0.1 46.9 3.5 km SSE of Fagradalsfjall
    2103 Wednesday 22.12.2021 22:05:16 63.874 -22.297 0.5 km 1.4 43.79 3.4 km SSW of Fagradalsfjall
    1723 Thursday 23.12.2021 05:14:41 63.882 -22.289 0.6 km 0.6 90.02 2.4 km SSW of Fagradalsfjall
    313 Friday 24.12.2021 14:45:51 63.878 -22.259 0.6 km 0.6 90.01 2.8 km SSE of Fagradalsfjall
    746 Friday 24.12.2021 05:52:13 63.891 -22.246 0.6 km 0.7 90.01 1.9 km SE of Fagradalsfjall
    1158 Thursday 23.12.2021 16:26:08 63.914 -22.24 0.6 km 0.4 72.92 2.1 km NE of Fagradalsfjall
    1339 Thursday 23.12.2021 11:51:05 63.889 -22.257 0.6 km 0.5 67.42 1.7 km SSE of Fagradalsfjall
    198 Friday 24.12.2021 15:59:29 63.882 -22.278 0.7 km 2 90.02 2.3 km S of Fagradalsfjall
    798 Friday 24.12.2021 05:16:43 63.832 -22.105 0.7 km 1.2 90.02 6.4 km SSW of Krýsuvík
    1198 Thursday 23.12.2021 15:31:00 63.877 -22.276 0.7 km 1.5 90.02 2.8 km S of Fagradalsfjall
    1524 Thursday 23.12.2021 09:09:09 63.86 -22.393 0.7 km 1.6 90.02 3.4 km NE of Grindavík
    86 Friday 24.12.2021 17:33:25 63.887 -22.261 0.7 km 1.2 90.01 1.8 km SSE of Fagradalsfjall
    328 Friday 24.12.2021 14:34:40 63.849 -22.351 0.7 km 0.9 90.01 4.6 km ENE of Grindavík
    392 Friday 24.12.2021 13:55:06 63.897 -22.244 0.7 km 0.3 90.01 1.6 km ESE of Fagradalsfjall
    403 Friday 24.12.2021 13:47:15 63.894 -22.246 0.7 km 1.7 90.01 1.7 km SE of Fagradalsfjall
    1172 Thursday 23.12.2021 16:00:44 63.869 -22.293 0.7 km 0.7 87.59 3.8 km SSW of Fagradalsfjall
    1532 Thursday 23.12.2021 09:02:42 63.862 -22.291 0.7 km 1.8 73.71 4.6 km S of Fagradalsfjall
    1443 Thursday 23.12.2021 10:12:49 63.868 -22.27 0.8 km 1.3 90.01 3.8 km S of Fagradalsfjall
    1946 Thursday 23.12.2021 00:28:21 63.874 -22.243 0.8 km 1.2 90.01 3.5 km SSE of Fagradalsfjall
    2133 Wednesday 22.12.2021 20:47:20 63.877 -22.259 0.8 km 0.1 90.01 2.9 km SSE of Fagradalsfjall
    1164 Thursday 23.12.2021 16:17:13 63.88 -22.288 0.8 km 0.1 47.87 2.6 km SSW of Fagradalsfjall
    1162 Thursday 23.12.2021 16:19:54 63.837 -22.36 0.8 km 0.5 31.16 4.1 km E of Grindavík

  18. Two mag 4+ NE of Grindavik.
    24.12.2021 21:38:59 63.879 -22.404 5.0 km 4.0 99.0 4.8 km NNE of Grindavík
    24.12.2021 21:38:22 63.854 -22.407 4.5 km 4.3 99.0 2.5 km NE of Grindavík

    • Friday
      24.12.2021 21:38:59 63.879 -22.404 5.0 km 4.4 99.0 4.8 km NNE of Grindavík
      24.12.2021 21:38:22 63.854 -22.407 4.5 km 4.8 99.0 2.5 km NE of Grindavík

    • Not at all good news if an eruption started so close to Grindavik. I am hoping it kicks of again in fagradsfjall area again. Safer there. I feel sorry for the volcanologists monitoring this currently. No holiday likely for them for the next few days, so hopefully they are able to take turns at the monitoring.

      • The quakes at Grindavik are triggered quakes. When the tip of the dyke propagates, there’s a lot of strain along a line through the tip and perpendicular to the dyke. This strain will trigger earthquakes in any faults along this line. In other words, it looks like the dyke is continuing to expand south. Remember that it failed to erupt here in March and went up closer to the center of the dyke instead. I think that’s the most likely scenario now as well.

        • I really hope that is the scenario that will end up playing out. I loved watching the eruption early this year as no ones life was at risk. Thankfully i think you have it right and there will be minimal disruption for Grindavik.

  19. Here’s the last 48 hours animated quakes at Fagradalsfjall:


  20. Thinking about what happened in March, the dike reached its maximum extent on about the 12th, or shortly thereafter. The eruption began about 1 week later. This time it seems the whole process has gone much faster, probably because the weakness was already there so the new dike basically just reopened the old one. An eruption is probably going to happen this week, before New Years.

    Now to see if it returns to the existing vent or if a new vent opens further to the south. Something to remember is the last eruption basically filled in all the topographic lows, so wherever this eruption happens the lava could flow further than it did last time.

    • This scenario is reminding me of that wonderful pressure ridge article, and also the cracks opening up on Theatre Hill.
      Are there any other areas of weakness that have emerged?

      • The only one with magma in it now is from Keilir to Natthagi, probably the deep source to this dike is somewhere south of Keilir where it was thought an eruption would happen a few months ago. Seems now we have a repeat event it is more likely for eruptions to stay in Fagradalsfjall though.

        There is another fault under Grindavik that is being stressed by the activity. In March this was happening on the 15th, only 4 days before the eruption, so maybe we are further along now than I thought 🙂

  21. I’m not calling this until I see tremor, or tornillos, on the Faf HighPass 2.0Hz chart.
    It is on its way, but not here yet.

    I’m interested in the idea an eruption may pop up south of the land-based Mar that cuts west to east just south of the Geldingadalir vent. Could the dyke really have jumped the Mar? Is there evidence for that happening?

    My opinion is we will see either a reactivation of the recent vent, or a fresh eruption to the north close to, or at Keilir, which is a fairly recent (geologically speaking) access route from dykes to the surface.

    That’s my two pennies worth. Referrals to the local clinic will be welcomed if I am proven wrong. 🙂

    • Wherever it ‘pops up’ it is certainly looking that it wont just go to sleep again. I say that on the basis of the faf tremor chart.

      • Sorry, I I was referring to the drum plot chart. But yes, that one’s looking rough, too.

  22. Courtesy of Google Translate – (source: in Icelandic)

    Earth has shaken the Reykjanes peninsula tonight. The largest earthquakes were at 21:38; 4.8 and 4.4 in size. They were found in many places in the southwest corner of the country. Shortly afterwards, at At 21:43 there was an earthquake of magnitude 4.1. These earthquakes were north of Grindavík.

    Kl. At 18:28, a magnitude 4.3 earthquake shook Stóri-Hrút. More than earthquakes have been recorded since midnight. There is no sign of eruptions.

    Today at At 15:03, a magnitude 4.7 earthquake shook Stóra-Hrút in Geldingadalur.

    On December 21, the earthquake began at Fagradalsfjall. About 9000 earthquakes have been detected since the beginning of the hurricane. The largest earthquake was 4.9 on the morning of December 22 and was felt well in the SW corner.

    More information in the news

    The reviewed earthquakes can be examined in more detail in Skjálfta-Lísa
    9,000 quakes is a lot!

    • At least there are no floating sofas to worry about…! (I’m referring to that Coastguard/pumice search earlier in the year.)
      I wonder how the locals are feeling about it? They must be getting a bit fed up with the rattling. Personally, I’d love to experience it – something that is missing in leafy Surry, UK.
      Thanks for the update!

      • Once it starts erupting the quakes will stop, and the tourism industry will be happy 🙂

        Probably a good idea to relocate the parking though, maybe have a regular tour bus from Grindavik to bring you to the start of the trail. If the eruption begins above the spot with the highest quake density then it will erupt on trail A so could end up being very accessible.

        Not sure we should expect an eruption at Keilir, the deep path seems to be near there but it is not near the surface, the shallow magma is all under Fagradalsfjall. Maybe later on if there is a large pile of lava on Fagradalsfjall it might tempt the dike to erupt closer to the origin but I think if it was going to do that at this stage it probably would have begun there back in March. I think it is more interesting having it on a mountain though anyway, makes for a lot more varied terrain and potential for a really impressive new volcano when it is all done 🙂

        • I wonder if some historic eruptions get greatly overestimated. If Geldingadalir sees decades of eruption it might cover the ridges and the high plateau of Fagralsjfall. We know those existed prior, but imagine if it happened long ago. Carl or Albert would look at the giant mass, calculate how much it rises above the surrounding terrain, and overestimate the volume by a couple km^3. Various subsurface imaging might correct that, but only if some researcher actually used them on the particular shield.

          Yeah, I would think there is a good chance it breaks out somewhere along the chain of cones. That area is now a weakness running above the top of the rift.

          • I think by the end of this event, whenever that is, there will be a line of shields and cones across the summit of Fagradalsfjall. Certainly this will be a very different sort of eruption than the fast fissure eruptions from Krysuvik and Svartsengi on either side.

            Looking at it, both of those places in the early Holocene also were dominated by shield eruptions, then fissures. I wonder if maybe Fagradalsfjall just didnt partake after creating Þrainsskjoldur, so now is effectively a hard restart. It is said no Reykjanes volcano except Hengill is a central volcano, but the only real difference between Hengill and Krysuvik is some minor silicic rocks at the former, otherwise both are similar. So Svartsengi and Krysuvik both probably have a magma chamber, just not one shallow enough to collapse. Fagradalsfjall might behave more like this if it can create a magma chamber too, and a long lived voluminous eruption or something similar would be a good way to create a chamber like that initially.

            Or maybe it is a bit of a one in 10000 years event like Lanzarote.

    • Are the building codes eathjquake-proof in Iceland?
      In the UK during fracking people claimed structural damahe from cat 2 quakes ….

      Here we have almost 5’s!

  23. The cubic kilometer measure of lava volume always throws me off because the number looks so small but the volume is so large. That .18 km^3 would mean 10 square kilometers covered with 18 meters in lava.

    Sorry, that’s just thought I had to get out while I’m reading this.

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