Category: Harmonic tremors

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Strong harmonic tremor pulse starting in Katla volcano

There seems to be a strong harmonic tremor pulse starting in Katla volcano. I do not think that this is anything else for the moment. I do not have any more details at the moment. But I am going to post updates when I know more.

Start of the harmonic tremor pulse on the SIL stations that he appears best on.


Slysaalda, north of Katla volcano. Copyright of this picture belongs to Iceland Met Office.


Rjúpnafell, South-west of Katla volcano. Copyright of this picture belongs to Iceland Met Office.


Lágu Hvolar SIL station. Copyright of this picture belongs to Iceland Met Office.


Álftagröf SIL station. South of Katla volcano. Copyright of this picture belongs to Iceland Met Office.

The start of the harmonic tremor event can be seen on the end of harmonic tremor chart. It stands out as it above the background noise on the SIL station. Next update on the SIL stations (10 or 20 min until it happens) is going to show more how big event this is going to be.

More updates when I know more on what is taking place in Katla volcano.

Update 1: The Public Civil Emergency Authority (Almannavarnir) in Iceland has increased monitoring with Katla volcano. But they have not declared any emergency level yet. Announcement about that in Icelandic can be found here. But scientists where flown over Mýrdalsjökull glacier at 18:00 UTC today (6. September 2011).

According to the news there has been increase in conductivity in Múlakvísl river. But for the moment the water level has not increased. There has been speculation that the tremor was created by water on the move. But that is unclear at the moment, however it is quite possible that more water is on the move under Mýrdalsjökull glacier.

Currently the harmonic tremor in Katla volcano has dropped back to normal levels. For the moment everything is quiet in Katla volcano. But that can change at any time without any warning.

News about this in Icelandic.

Órói undir Mýrdalsjökli (Rúv.is)
Fylgjast með aukinni virkni í Kötlu (Vísir.is)
Eftirlit aukið með Kötlu (mbl.is)
Flogið yfir Kötlu (mbl.is)

Update 2: It seems that a new harmonic tremor episode is about to start in Katla volcano. So far it has remained small. But it is impossible to know if that is going to change suddenly or not. Update 2b: There is also some wind noise on the seismometers around Katla volcano. This wind is increasing background noise. It often look like a tremor increase, while in reality it is not.

Blog post updated at 18:37 UTC.
Blog post updated at 18:46 UTC.
Blog post updated at 20:03 UTC.
Blog post updated at 20:29 UTC.

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Growing harmonic tremor spike in Katla volcano

It seems that Katla volcano is going to keep me busy for coming days and weeks.

At this moment it seems that there is a growing harmonic tremor in Katla volcano. This harmonic tremor started today after the earthquake swarm that took place earlier today. After it stopped a spikes of small harmonic tremor spikes did start to appear. During the past few hours they have been growing in size. But it seems that the harmonic tremor drops for few moments between spikes.


Earthquake swarm that took place yesterday in Katla volcano. Copyright of this picture belongs to Iceland Met Office.

This earthquake swarm was mostly small one. With largest earthquakes going up to around ML2.1.


Slysaalda SIL station. Harmonic tremor appears poorly on this SIL station. Copyright of this picture belongs to Iceland Met Office.


Rjúplafell SIL station. The harmonic tremor signal can be seen here clearly, even if it a small one. Copyright of this picture belongs to Iceland Met Office.


Lágu Hvolar SIL station. The harmonic tremor signal can be seen poorly on this SIL station. But it signalled with minor change in the background noise on this SIL station. Copyright of this picture belongs to Iceland Met Office.


Álftagröf SIL station. The harmonic tremor spike can be seen most clearly here, as it goes clearly above background noise. Copyright of this picture belongs to Iceland Met Office.

From what I can tell this harmonic tremor signal is growing every few hours or so. It is possible that this is a repeat of what did happen in July. But for the moment it is too early to know that for sure at the moment. But for the moment there is no eruption about to start in Katla volcano.

When I was writing this blog post, it seems that a new earthquake swarm is about to start in Katla volcano. But the earthquake swarms in Katla volcano often start slowly with few earthquakes, but they seems to grow with time.

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New harmonic tremors spikes in Katla volcano

This has become almost a daily occurrence. But today there was one harmonic tremor spike (at least) in Katla volcano. It is unclear why this harmonic tremor spikes happen in Katla volcano. But they often do happen just before a earthquake swarm starts, but often several hours before (sometimes). I am not sure why that is. But one idea is that this activity is connected to hydrothermal areas that are under the Mýrdalsjökull glacier.

Earthquake activity has been quiet in Katla volcano today. But it is hard to know for sure if that is going to last. As earthquake activity appears to be on the rise in Katla volcano during the whole of the year 2011 according to news in Iceland (see earlier blog post for details).


Harmonic tremor spike as seen on Lágu Hvolar SIL station. The spike is between 04/09 and 05/09. The spike is a small top in the tremor chart (hard to spot). Copyright of this picture belongs to Iceland Met Office.


Harmonic tremor spike as seen on Snæbýli SIL station. The spike is between 04/09 and 05/09. The spike is the broad band that suddenly appears in the tremor data. It is easier to see then on Lágu Hvolar. Please note that it seems that Snæbýli SIL station has gone offline again, as it has stopped updating. Copyright of this picture belongs to Iceland Met Office.

It is clear that Katla volcano is going for a eruption. But the question remains is just when that is going to be, but it is impossible to predict when a eruption is going to take place in Katla volcano. But the signs have come clear in my opinion in this matter. For the moment it is just waiting and watching. But this might be a long wait until something happens in Katla volcano.

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Earthquake swarm in Katla volcano

Today (3. September 2011) at 16:45 UTC a earthquake swarm did start in Katla volcano. So far this earthquake swarm has been small, with the largest earthquake just with the size ML2.7 at the depth of 1.1 km (automatic data). But the quality of this earthquake was good, so location is accurate from what I can tell.

I am not sure at this moment if there is a harmonic tremor spike following this earthquake swarm or not. As the earthquakes are long period due the fact that they are created by magma movement in Katla volcano. This might be dike intrusion. But for the moment it is hard to know that for sure.


The area of earthquake activity today in Katla volcano. Copyright of this picture belongs to Iceland Met Office.


The ML2.7 earthquake (automatic size) in Katla volcano caldera. This picture is released under Creative Commons Licence, see Licence web page for more details.


Harmonic tremor plot of the current activity. Latest activity is at the end of the tremor plot. Copyright of this picture belongs to Iceland Met Office.


Harmonic tremor plot of the current activity. Latest activity is at the end of the tremor plot. Copyright of this picture belongs to Iceland Met Office.


Harmonic tremor plot of the current activity. Latest activity is at the end of the tremor plot. Copyright of this picture belongs to Iceland Met Office.

I cannot tell at the moment what is going on in Katla volcano. But the earthquakes tell me that the reason why they are happening is because of magma is moving inside Katla volcano. But latest data (not shown here) do however show that no harmonic tremor is currently ongoing, if it ever started during this earthquake swarm. I am expecting the earthquake swarm to continue and last for the next few hours. But I must point out that that is what might happen, as sometimes earthquake swarms just stop when you think that they might be about to start for real.

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Minor harmonic tremor in Katla volcano

There seems to have been minor harmonic tremor in Katla volcano this evening. This harmonic tremor seems to have started after a ML0.7 earthquake with the depth of ~3.7 km did happen inside the Katla volcano caldera. Last harmonic tremor spike did take place on the 24th of August according to the tremor plot on Icelandic Met Office web page.


Harmonic tremor mixed in with the earthquakes from Katla volcano on this tremor plot. Copyright of this image belongs to Icelandic Met Office.


Here is the harmonic tremor that I see on the tremor plot. It is the second spike. But the first spike is actually a earthquakes that did happen earlier today. Copyright of this image belongs to Icelandic Met Office.


This harmonic tremor can also be seen on this SIL station clearly. Copyright of this image belongs to Icelandic Met Office.

On other SIL stations around Katla volcano the signal is not so clear. But this is really a small event and unlikely a pre-eruption event. But it is hard to know it for sure, as Katla volcano has done this before and there was no eruption following this type of events. All that can be done now is to wait and see what happens next. It is also important to notice that Icelandic Met Office has not confirmed this harmonic tremor spike yet.

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Background noise compared to a eruption and other events

Here are few examples of how the tremor plots looks like if anything important is going on in Iceland.


Normal quiet tremor plot. Few earthquakes create spikes on it. But besides that everything is quiet. Copyright of this pictures belongs to Icelandic Met Office.


This is from the Grímsfjall volcano eruption in May 2011. On this tremor plot it can be clearly seen how much noise a eruption actually makes. The background noise just goes away soon as there is something going on. Copyright of this pictures belongs to Icelandic Met Office.


This is Skrokkalda SIL stastion on 12 July 2011. It can clearly be seen where the harmonic tremor goes above the background noise. Copyright of this pictures belongs to Icelandic Met Office.

It is quite clear. Besides earthquakes and some harmonic tremors that are different then this signals that I have shown here. Unless you see this on Icelandic Met Office tremor plot you can be sure that it is quiet in Iceland. Volcano eruptions make a lot of noise when they are ongoing, even the small eruptions make some noise that can be detected by the SIL network in Iceland.

Note: I might update this blog post on later date and put in more examples about the difference between background noise and a eruption.

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Overview of Hamarinn volcano current activity

Here is a short overview of the Hamarinn volcano activity this summer. From what I can gather in the current data this is most likely not over. During the past few days there have been at least suspected two minor eruption in Hamarinn volcano. But it hard to confirm it due to glacier that is covering this area.

This all starts on 12. July 2011 at 07:30 UTC with this event here.


The tremor spike on 12. July 2011 at 07:49 UTC. Copyright of this picture belongs to Icelandic Met Office.

When the clock is around 19:10 UTC the same day the tremor chart looks like this.


The tremor spikes are now three on 12. July 2011 at 19:09 UTC. Copyright of this picture belongs to Icelandic Met Office.

On the 13. July 2011 the tremor plot looks like this. But at that time the glacier flood had started and broken from the Vatnajökull glacier.


The tremor chart at 13. July 2011 at 01:10 UTC. Copyright of this picture belongs to Icelandic Met Office.


The tremor chart at 13. July 2011 at 12:59 UTC. Copyright of this picture belongs to Icelandic Met Office.

Then there was a short period of break when nothing interesting happened in Hamarinn volcano. That break did last until 16. July 2011 when a new, but smaller spike did appear on Skrokkalda SIL station.


The tremor at 16. July 2011 at 15:22 UTC. It is not fully clear what did happen at this time. But this was most likely a earthquake in Hamarinn volcano. But that is yet unconfirmed at this time. Copyright of this picture belongs to Icelandic Met Office.

Then there is a new break that lasts until 1. August when a earthquakes happens deep under Bárðarbunga volcano. But the deepest earthquake had the depth of 25.2 km. But it is also important to notice this earthquake that took place on 13. July 2011 and it is from Hamarinn volcano.


The earthquake from Hamarinn volcano. This picture is released under Creative Commons licence. Please see licence web page for more details.

On the 3. August 2011 around 02:00 UTC a new harmonic tremor spike starts to be visible on Skrokkalda SIL station.


The tremor plot at 01:55 UTC on 3. August 2011. Copyright of this picture belongs to Icelandic Met Office.

This day two minor harmonic tremor happens. A change in Skaftá glacier river is noticed. That is higher conductivity and slightly more water. It was announced in the news that a Skaftá glacier river flood was about to start from the eastern glacier cauldron that is formed above the Hamarinn volcano. Today however that does not seem to be the case. As no glacier flood has taken place so far.

Today (5. August 2011) there was a new harmonic tremor spike on Skrokkalda SIL station. It did follow the same pattern as before. It started and lasted for about 20 to 60 minutes or about that long.


The tremor chart 5. August 2011 at 17:38 UTC. Copyright of this image belongs to Icelandic Met Office.

So far today only one harmonic tremor has been detected. But given the past experience that is unlikely to hold for a long time now. But it is impossible to know when a new event starts or how big it is going to be.

The original event on 12. July 2011 did create new cauldron in the glacier. This map from Icelandic Met Office shows the location of those new cauldrons. But it has been marked with a star on the map. The coloured dots are earthquakes in this area over the past few years.


Map of the area that is currently active in Hamarinn volcano. Copyright of this image belongs to Icelandic Met Office.

Given the current data I am expect a full scale eruption in this area soon. When is hard to know for sure. But until that happens there are going to be more smaller eruptions in this area. I do not know why there is a lack of earthquakes following this events. I cannot explain it. But because of that this can only be seen after it has started on the tremor charts.

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Sharp rise in harmonic tremor on Skrokkalda and Grímsfjall SIL station (among others)

There is a sharp rise in harmonic tremor on the Skrokkalda and Grímsfjall SIL station. I do not know yet what volcano is responsible for it. But the Hamarinn volcano is a suspect at the moment.

Current tremor plot.


The tremor spike is at the end of this tremor plot. Copyright of this picture belongs to Icelandic Met Office.


The tremor spike is at the end of this tremor plot. Copyright of this picture belongs to Icelandic Met Office.

I am going to post more information about what is going on when I know more. This blog post might get updated soon if needed.

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Small glacier flood from Mýrdalsjökull glacier (Katla volcano)

During the night (and when I had unstable power) there was a small glacier flood from Mýrdalsjökull volcano. Some minor harmonic tremor change was detected following this glacier flood. This even was small one, many times smaller then what did happen on the 8 to 9 July 2011. Due to security concerns the Civil Emergency Authority did close the main road in Iceland for this area. Since they never know how big the flood can actually be. The main road was closed for about one hour. This glacier flood was detected around midnight 20 to 21 July 2011.

This flood is actually so small it is hard to see it on the harmonic tremor plot from the SIL stations around Katla volcano.


Tremor plot from 07:50 UTC this morning. It is hard to see the harmonic tremor from this minor glacier flood. Copyright of this image belongs to Icelandic Met Office.


Tremor plot from 07:50 UTC this morning. It is hard to see the harmonic tremor from this minor glacier flood. Copyright of this image belongs to Icelandic Met Office.


Tremor plot from 07:50 UTC this morning. It is hard to see the harmonic tremor from this minor glacier flood. Copyright of this image belongs to Icelandic Met Office.

What happens next is impossible to know for now. But it seems that activity continues to be high in Katla volcano. All that can be done is to wait and see what happens. But I am going to continue to monitor the changes in Katla volcano as best that I can do until I finish my summer job (29. July).

Icelandic News about this.

Aukin leiðni í Múlakvísl og órói í Mýrdalsjökli (Vísir.is, Icelandic)
Náið fylgst með Mýrdalsjökli (mbl.is, Icelandic)
Hringvegurinn opinn á ný (Rúv.is, Icelandic)
Breytingar í Múlakvísl (Rúv.is, Icelandic)

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Small harmonic tremor spike from Hamarinn volcano

There seems to be a small harmonic tremor spike taking place in Hamarinn volcano (Bárðarbunga volcano) at the moment. This tremor spike is not strong at the moment. This tremor spike appears to have been pre-seeded by few long period earthquakes (not all of the earthquakes seen on Skrokkalda are from Hamarinn volcano, few are from Katla volcano), but that suggests that magma is on the move in Hamarinn volcano. But this would the second harmonic tremor in a time period of 48 hours it seems.


The harmonic tremor spikes can be seen at the end of this tremor plot. Copyright of this picture belongs to Icelandic Met Office.

Currently it is impossible to know what happens in Hamarinn volcano. As it’s pre-eruption behaviour is rather unknown. But if there is a eruption in this area I am expecting a lot of earthquakes, with size well over ML3.0.

Blog post updated at 16:20 UTC.