El Hierro – Day 7

Photograph by Cestomano. The lighthouse of the Orchillas was once known as the end of the world. Under this lighthouse is where the new magma chamber is forming.

This will mainly be a short update. Not much new has happened during the last few days, I will just try to explain why.

What we are seeing now is the formation of a new part of the magma chamber(s) under the island of El Hierro. The progression of earthquakes that we have seen moving roughly from Tanganasoga volcano towards the WSW is magma following a weak seam between two rock layers in the crust. This is creating a rather low, but wide, layer filled with magma. You can think of it as a cake, where the magma is a layer of custard cream between two pieces of bread.

Initially I thought that this layer would not be able to take a lot of magma before the magma would break through into the two older layered magma chambers that were created before the last eruption. My line of thinking was that as soon as that happened magma would move up into the old feeder channel leading towards the volcanic vent known as Bob south of La Restinga.

Image by IGN. The darkblue and read area is where a new magma chamber has started to form like a stacked layer in a cake.

Instead a large quantity of magma has gushed into this new formative magma chamber, which is continuing to grow. There is a rule in fluid dynamics that state that as a bladder (balloon) grows the rate of growth will decrease as the volume increases. This is why it takes more and more magma to keep the pressure at a constant level during the expansion. This is why we see fewer earthquakes as the size grows. It takes a larger amount of magma going into the system to create the pressure for the earthquakes to happen. We will also soon see that the rate of rapid uplift will be decreasing. Do not take this as a sign of the risk for an eruption decreasing. It is quite the opposite. Why? The rate of magma arriving is still constant, so, in due time it will break through.

Magma seems to have entered into the old feeder channel to Bob, how far up though is anyone’s guess. But, it seems to have stopped flowing upwards now, probably due to the opening being plugged up.

Instead we are now seeing a small amount of earthquakes entering into the zone between 16 and 8 kilometers from the surface. What is most likely is that we will see more of them during the next 48 hours; with a bit of luck we will be able to pinpoint the formation of an earthquake stack. That would be good since that could point towards a general area where there could be an eruption. Currently that is pointing towards the western area of the island, but that might change rapidly.

Image by IGN. A few earthquakes have started in the 16 to 8km depth range.

When the magma enters the region 8 kilometers and above the earthquakes will most likely stop, or be few and far apart. The reason for this is that there is a layer of old sediment there. Then there will be a brief flurry of earthquakes as the magma breaks through to the surface, unless it finds an old lava-tube, then it would be a quiet onset of eruption. The eruption would be of basalt or basanite, so it would most likely be a quiet effusive eruption. In the beginning it could be more vigorous due to gas pressure release.

I would still not rule out that the eruption will happen somewhere along the old feeder channel that lead out to Bob. If that happens I believe the eruption to happen somewhere closer to land than during the last eruption. It could also happen on land.

During this second phase of the eruptive cycle the level of information given out has been much improved. IGN is now giving out real GPS data instead of cumulative data. That is a huge improvement. Also Pevolca has started to write reports that are filled with technical details that helps a lot, and removes any chance of people accusing them of hiding data. If IGN and Pevolca keep up with this new openness they will find that people will be much happier. So, from us a big thanks for this new approach.

I would also like to point out to the political establishment of El Hierro that the last eruption will in the end be a big boon for the Island. Before nobody pretty much knew that El Hierro existed. Now many do. And that should in the end raise the number of visitors, especially from the rather large cadre of volcano aficionados. So, instead of trying to hide your volcano, flaunt it a bit. Be proud of it, and people will come to watch your beautiful island.

CARL

El Hierro – Day 3!

Photograph by photosaereasdecanarias.com Tanganasoga volcano, one of the possible places where the new eruption will occur.

Today we have seen a change in the behaviour at Pevolca, now they have changed the level of alarm from green all over the island, to yellow for Julan and La Dehesa. They are also asking everyone on the island to familiarise themselves with the plans for evacuation and self protection.

Image courtesy of IGN for Volcano Café. The image is showing the Seismograph station of Julan. It was during yesterday giving the highest values of all the stations on El Hierro. The center of the probable source yesterday was in the area from Tanganasoga to Humilladores.

The center for the current magmatic earthquake swarm has moved slowly since yesterday to the west and south. And the magmatic component of the waveforms have increased in clarity. As you can see in the image above (provided directly by courtesy from IGN to Volcano Café) the center of attention yesterday was at Julan.

There has also been rapid inflation during the last two days with clear movement patterns associated with magmatic movement, and new magma arrival. The numbers are high for such a short time period, between 2 and 3 centimeters.

Commentator Vishy pointed me to a paper by Stroncik regarding chrystalization in magmatic chambers, and in this case the depth necessary is somewhere between 16 and 23 kilometers down. This means that the earthquakes we have seen in this depth region is where the magma chambers are.

Image by IGN. As you can see the band of red and blue is moving to the southwest. The area is showing part of the magma chamber system under El Hierro.

As you can see in the image this increases the risk for an eruption occuring in the southern fissure zone ranging from La Restinga up towards Tanganasoga. If a new feeder channel is opening up we will first see migratory earthquakes in the region between 16 and 8 kilometres, after that we will most likely see an onset of eruption within a few hours. It is therefore very important to study carefully the plots to see where the conduit is forming.

The likelihood of a new eruption starting is now very high. I would like to tell any readers of this blog who lives on El Hierro to check often for new data, especially the IGN Earthquake positioning map. If you live in the area ontop of where the earthquakes are forming in the 16 – 8 kilometer depth level, you would do well by moving yourself away to safer grounds, best and safest part is to the northeast on the island (very low risk for eruption there). You are of course welcome to check in here also for new information in the comments, if anything happens it is most likely to find the information you need there.

http://www.01.ign.es/ign/resources/volcanologia/jpg/Eventos_HIERRO_2D.jpg

Image by IGN. A nice and very clear image of a Longperiod Earthquake (LP event). Thanks to commenter Judith who pointed it out for me.

CARL

El Hierro – Day 2

The face of El Hierran politics, Alpidio Armas.

This will just be a short update with the information that has come at hand.

There seems to be a full on war between Pevolca, Involcan and José Luis Barrera VP of the ICOG (Spannish Association of Geologists). Pevolca has stated that there are some reneval of tectonic earthquakes, with no risk for the population or any need for any measurments to be taken. They also point out that there is no increase in gases. They do though mention that they will be watching things. They have also stated that there is no inflation at El Hierro (GPS).

Involcan has stated there is inflation after studying the GPS system of Professor Sagiya from Nagoya. They also point out that the reason for Pevolca not being able to see any heightened gas levels is that they have not measured the gas since April 5.

http://www.facebook.com/pages/INSTITUTO-VOLCANOLÓGICO-DE-CANARIAS/134042953295772

José Luis Barrera and the ICOG have issued a statement that the more than 350 earthquakes are tectonic, but that they might be a run-up phase for renewed volcanic eruption. They also note that the activity is unusual.

http://www.europapress.es/comunicados/noticia-comunicado-colegio-geologos-muestra-incertidumbre-repunte-actividad-simica-hierro-20120626152109.html

Meanwhile in the real World

While the Spannish authorities and organisations are involved in their usuall pissing contest there are some things worthy of comment.

A little tidbit on the earthquakes during the 48 last hours…
Yesterday had the fifth highest recorded number of earthquakes (241), the highest recorded number is close to 454, and that was in August as the former wad of magma had it’s peak of arrival.
But what is really interesting is that if one take a look at how those quakes break down into size…
Yesterday first, then August number-record.
0-2M 55 (448)
2-3M 180 (6)
3<M 8 (0)

And that would have made yesterday into releasing 5 times as much energy and destroying about 32 times as much rock. It was the record of all time energywhise. This leads me to believe that the amound and speed of arrival is higher this time around. So, the last two days have had the largest accumulated seismic energy release since onset of activity at El Hierro. Energy record in short. And that is note noteworthy according to Pevolca.

LP Earthquakes

The earthquakes today has long amplitude component to them normally associated with magmatic movement into the cracks. These LP earthquakes is considered to be magmatic. There has during the last 8 hours been at least 3 of them. The 17.16 is one of them.
I believe this is onset of movement upwards of magma into the actual system of Tanganasoga.

First LP

Image by IGN. The First LP Earthquake.

Second LP

Image by IGN. The Secong LP Earthquake.

Third LP

Image by IGN. Third LP Earthquake, and what is most likely onset of a heavy magmatic intrusion upwards.

The third LP seems to have opened a conduit somewhere, most likely from the crustal boundary (MOHO) up to the chamber under Tanganasoga, or directly towards Bob. The Long Periodicity Earthquake is caused by an initial earthquake that opens up a fissure, sill or dyke, after that magma moves in to fill the opening, and that creates and unusual type of earthquakes.

Conclusion

There is no reason that I should recant on what I wrote yesterday. I still believe that there is a rather high risk of a new eruption at El Hierro. I still see no reason to not believe it will be in the southern part of the island, or out in the ocean south of La Restinga. I still feel that La Restinga is not entirely safe for it’s population.

Update

While I was writing this post the signal changed sufficiently for me to believe that there is risk that the eruption is either about to start, or has already started. We are all waiting for news, and think about the unprotected civilians in El Hierro.

CARL

Eruption warning for El Hierro

The earthquake that started either the pre-eruptive run up, or a new eruption.

On the seventeenth of June a new phase of increased earthquakes was observed by commentators on this blog. The level of seismicity was both larger and more numerous than during the previous 3 months. The location of these earthquakes corresponded with the place where the first earthquakes happened during the run up to the previous eruption.

As I have said before, when new magma comes up from the deep via the mantle plume we would see earthquakes at this spot. On the twenty-second of June low frequency harmonic tremor started at two distinct frequencies (0,29 and 0,59Hz) that previously has proved to be related with renewed activity. The frequencies are believed to be a sign of new magma arriving from the deep.

At 21.23 hours on the twenty-fourth of June (yesterday evening) an earthquake of magnitude 3.1 occurred, and within minutes the harmonic tremor had increased in sufficient numbers to herald movement of magma up the magmatic conduit system. After that there has been 49 earthquakes ranging from 2M to 3.8M, which is a rather good sized earthquake swarm for an already active volcanic system.

It has been noted that the earthquakes are not at the exact spot where they were during the previous eruptive phase. The answer is rather simple, the previous earthquake loci have by now gone above the solidus point and is not any longer brittle enough; therefore the renewed pressure breaks the adjacent rock. In other words, the magma chamber has matured and evolved.

As the pressure started to build up from the recently arrived new magmatic material from deep it started to move towards the old conduit. This conduit is by now fairly blocked by solidified magma at the opening.

A renewed eruption will start somewhere along the old conduit leading south from the Tanganasoga volcanic system towards the old eruptive vents that build up the edifices of Bob south of La Restinga. The question is if the new eruption will take place at the original pillow lava and pumice cone of Bob, or up at the new vent slightly closer to La Restinga. Another option is that the old vents by now are to plugged for the lava to be able to escape that way. Then the most likely place is somewhere along the route of the old conduit. And that means closer to the town of La Restinga, or even on land close to or inside the town.

Currently I would say that there is a high risk of an eruption starting, or that it already has started. Visible signs of the eruptions should be coming within the next 3 days judged on previous behavior. The eruption will most likely not be larger than the previous one due to the pressure being lower, but if it happens closer to shore, or even on land, the effects might be more dramatic for the residents.

My judgment would have been to immediately evacuate La Restinga until the eruptive locus has been confirmed.

IGN and Pevolca has declined to comment on this.

Update:

Regarding why I wrote that unusual and stark warning directed to the residents of La Restinga. I want to clarify why.

1. From the current signs and previous behaviour of the Tanganasoga volcanic system I judge that there is a 2/3 risk for a new eruption soon.
2. I am fairly certain that Bob and the newer vent on the ridge above Bob towards La Restinga is congested by solidified lava and not viable any longer as eruptive vent.
3. During the end of the previous eruptive phase there was anomalous gas ventings closer to La Restinga, and 2 earthquakes located close to the port of La Restinga (one was inside the actual port).
4. We know that the conduit leads from Bob towards a magma chamber under Tanganasoga. The usual behavious for volcanoes of this type is propagating vents erupting ever closer to the central part of the volcano.
5. From all of this I judge it to be about a 50 percent risk that the new eruption would be sufficiently much closer to La Restinga to cause risk for the inhabitants, or even on land close to or inside La Restinga. One should remember that there is a scoria cone 100 meters outside of La Restinga.
6. The current harmonic tremor episode is of the broadband type that is normally associated with sudden heavy degassing caused by the earthquakes. This can in a few eruptions increase the likelyhood of a non benign type of eruption. Ie, that the next eruptive phase may be having a more vigorous start than the previous due to a lot of gas pressure building up.
7. IGN and Pevolca is not the most warningsome agencies on the planet, to put it mildly.

All of this put together gave me a bit of a judgement call crisis. Based on my consciense, my experience, and so forth I decided that someone should issue the warning that IGN and Pevolca most likely will not give. So, I gave a warning that I myself would adhere to. I personally would not be inside of La Restinga right now. I would rather have someone say I am an idiot and should shut up, or even in the end try to sue me, than feeling that I through being quiet was part in people dying.

I would though like to say that those who so far have questioned me (privately) have been quite correct in doing so, specifically since I was in a hurry when writing and therefore a bit vague.

Pevolca has notified that there will be a statement after their meating this afternoon, and also commented that the afternoon today was the fastest possible oportunity for the meeting regarding the current new activity.

Update 2

People have noticed down in the comments that the harmonic tremor is higher in frequency this time and look different. That is because it does.

Click on the image for a bigger view. Do not be alarmed by the text, what is stated there is about volcanoes that have had a long repose period.

The earthquakes have knocked off a lot of gas from the lava, and this causes something called a Broadband signal. These are normaly associated with more vigorous eruptions. The text in the image states the limit here as being a VEI-3 eruption following a broadband signal. But that is for a volcano that has been dormant for a while. At Tanganasoga the plumbing system is still in large parts open, so the pressure can not build up sufficiently to produce a VEI-3 eruption, and that most likely gives the broadband signal for a smaller possible event.

CARL

Bob – Why bother to stop erupting?

Photograph by Santiago Ferrero. Southern part of El Hierro.

The volcanic vent affectionately known as Bob, a part of the Tanganasoga Volcano, south of El Hierro has resumed its eruption. Many people have declared it dead, Pevolca, IGN and Nemesio Perez has together declared the volcano dead more than 20 times. Declaring an active volcano to be dead seems like a rather futile endeavor. Something the learned gentle-persons should have learned by now.

Yesterday reports started to come in that there was a visible disturbance in the waters south of La Restinga (El Hierro). About the same time there was a marked uptick in earthquake strength and number. The Earthquakes are deep, mainly between 15 and 25 kilometers in depth. The distribution of the earthquakes is well spread, this points towards it being a non-localized event, probably a shock-result as new magma arriving from the depth hits the underside of the crust.

Image by IGN. Earthquakes during the last 48 hours.

This is probably confirmed by the return of the 0.59Hz harmonic tremor visible at the CCAN and EOSO (Gran Canaria) SIL-station.

Image by IGN. Clear and visible harmonic tremor at 0.59Hz.

Today there have been reports at various sites (AVCAN among them) that there is now a visible stain, something that requires an ongoing eruptive process. Also, there is a photograph published at Earthquake Report showing a side scan SONAR image of the ongoing eruption.

Photograph of a sidescan SONAR image, source IGN (via Earthquake Report).

The image is very well defined, a sign of a large amount of coarser ashes and solids being suspended, and ejected upwards in the water. Light ashes and gases are less well defined than shown on the image. To the right one can see a spot where material is falling back onto the sea-floor. This is where the heavier aggregate looses buoyancy and gets separated from the lighter material.

Effects

I have written many times that as long as the eruption continues at Bob there is not any great risk for the island and its inhabitants. This is due to Bob functioning as a pressure release valve stopping pressure to build up enough for a catastrophic failure in the volcano proper’s overburden (the volcanic edifice of Tanganasoga).

The current spot of eruption is the original cone that started the eruption, not the later vent up on the ridge (a bit further to the right than the image shows). Last figure set the vent at 120 meters depth. The reason for it being lower now is that it is constructed mainly out of loose material (pillow-lava and tephra) that has both compacted due to its own weight, and been reduced in volume by the local currents in the water.

There is currently no indication that this new eruptive phase will stop any time soon since the earthquake activity is continuing to increase in frequency and strength.

Sadly due to the supression of GPS data by Involcan and its managing director Nemesio Perez there is no GPS data whatsoever that can be published. Due to this censorship we can not say anything about how and if the volcano is inflating. I find this behaviour despicable and dangerous for the residents of El Hierro. I would also state that it is sad that the webcams are now gone as a result of Alpidio Armas machinations.

CARL