A brief update on El Hierro

This image from the tourist bureau gives quite a good perspective on the island of El Hierro and La Restinga. One just need to lift the eyes to see the volcanic edifices looming over the villcage.

As the smoke starts to clear at El Hierro we get a much more detailed picture of what is happening. As data has poured in we can now deduce a few things.

First of all GPS figures today confirmed that this is indeed a fourth bolus of magma coming up from the depth.  The first one in July 2011 started the entire hubbub and in the end caused the sub-aquatic eruption south of La Restinga. A second bolus in January that followed the same path revigorated the ongoing eruption briefly, but was too small to keep up the pressure in the volcanic system and the eruption dwindled to a halt. The third bolus is so far the most interesting, during a few days more magma arrived than during the first one that caused the eruption. The magma arrived at the same place as for the first two (around the Tanganasoga volcano), but then it took an entirely new path and created quite a few earthquakes as it moved towards the western point of the Island. The fourth bolus also arrived at Tanganasoga, and immediately started to move south and slightly downwards.

Image by IGN. GPS data points for the uplift, figures are aproximatly 2 days old.

We still have only one set of data points for the GPS, but since it is visible on many of them it is still credible. What is a good test for if there is actual inflation or not is to check for motion in EW and NS directions. A false read normally does not show that.

The earthquake swarm is very vigorous with more then 100 earthquakes per day. The pattern is still continuing with a south and slightly down dipping motion. We will see if the hard tested village of La Restinga will have to suffer both the knowledge and the feeling of magma moving straight down under their feets.

Image by IGN.

We can also rule out any degassing or actual small eruption, what initially looked like harmonic tremor are most likely small earthquakes, there is no clear signal showing harmonic tremor to this date.

Image by IGN. No harmonic tremor showing on the charts now. So, no eruption, or no de-gassing.

There is no way to know if this bolus will cause an eruption or not. The lack of harmonic tremor says that it will at least not happen within the next 24 hours or so. But, for the residents on El Hierro the same advice is always valid, stay on top of the news.

CARL

Salud El Hierro!

The thermal hot spring bath of Balneario Pozo la Salud. Quite likely the new “to be at” spot for Jacuzzi watching.

The volcanic island of El Hierro is really turning into the Little Volcano that Could.

3 earthquakes seem to have changed the ballgame around once more.  First came two deep earthquakes at a new spot at 10.10 in the morning, both of them at the depth of 20 km. 26 minutes later followed a 2.6M at 10 kilometers depth.

Within minutes a sharp increase was noticed in the high frequency tremor. The tremor lacks low frequency components making this a dead giveaway that we are seeing a de-gassing event. What has happened is that a persistent earthquake swarm north of Balneario Pozo La Salud most likely finally cracked through and things started to move up beyond the de-gassing threshold.

Image by IGN. Please notice the lack of tremor at the lower frequencies.

After the 10.36 earthquake the shallower earthquakes pretty much disappeared and we had an onset of a new active deep earthquake swarm. In retrospect it is clear that we most likely caught the arrival of a new bolus of magma arriving from depth. If so it is the fourth time new magma arrives from the depth.

The deep earthquake swarm roughly follows the same pattern as for the previous 3 arrivals. Activity started at 20 kilometers depth at Tanganasoga, and then moved outwards and slowly dipped deeper. Every arrival has taken a slightly different direction; this one is moving into what can only be seen as pristine territory.

Image by IGN. Notice the 10km swarm north of Pozo la Salud, and the arrival of the new magma at 20km around Tanganasoga, this time moving roughly towards La Restinga area with a slow dip downwards. Remember that it never went this way during the Eruption of Bob south of La Restinga.

It is still too early to see anything on the GPS, but it should start to be visible tomorrow.

Question then is where is the de-gassing happening? My guess is that the guests of Balneario Pozo La Salud might have an interesting wake up call. If they are lucky they will have a brand new hot water Jacuzzi out in the ocean. For those who do not know, Pozo La Salud is a thermal spring bath in El Hierro.

CARL

Friday riddle is still unsolved:

I am the stony product of music that make Pavarotti mate a canis canis sheep mixture, I am spawned out of the apothecary.

What am I? And what is my origin? 3 points to be had, 2 for the name of “What am I”, and 1 for the origin. There is also a cunningly hidden bonus point out there…

El Hierro – What did Elvis have to do with the Island?

Photograph by unknown. Orchilla Lighthouse, famous for being “The end of the World”.

During the night life got fairly interesting in El Hierro as the residents woke up from no less than two earthquakes above 4M. The larger of these two reached 4.4M.

Otherwise it seems like the magma continues to move in a general southwesterly direction. This has had as an effect that many of the GPS stations on the island is registering a downfall. It is at the moment uncertain where the magma is going.

The activity that we have seen during the last weak and a half is a sill intrusion, or a horizontal oblong shaped flat intrusion between different layers of rock. The intrusion has happened at great depth, around 20 kilometers deep. The activity started roughly under the old volcano of Tanganasoga, and then progressed towards the south east, passing the famous lighthouse of Las Orchillas on the way. The lighthouse is famous for being called “The End of the World”, a strangely fitting denominator when taking the current activity into account.

If we look closer at the 4.4M earthquake it had some rather intriguing features. It had a very weak transient in the beginning. The transient is the initial earthquake that is starting the rift of the fault plane, it was around 1.9M in this initial phase. After that a heavy magmatic component started as magma gushed in to fill the void left by the earthquake, and as the magma entered it further delaminated the layers in the rock, and more magma flooded in and so on and so forth. Let us just say that it was a lot of magma moving very rapidly.

Image by IGN. The earthquake starts at roughly 41 minutes, and it continued for 6 minutes before ending.

The angle was also rather interesting. The fault plane was tilted at 134 degrees, so the propagation of the earthquakes fault plane was going upwards at an angle. This gave the earthquake a fairly hard profile to plot, and both location and depth was changed due to this. Initial depth was set at 12 kilometers, as that was the end point of the faulting, but the beginning of the faulting was at 21 kilometers. And at an angle of 134 degrees this makes the start and finish line of the earthquake being somewhat different in location.

The earthquake was both Long Period, and a of the Broadband type. What I like to call a wet earthquake as oposing the dry earthquake that is associated with tectonic movement. It also look quite a bit like the sonic signature of water moving unexpectedly in a tube.

Worried in El Hierro?

The activity is right now inconclusive. The activity has started to show higher up, but the bulk of the earthquakes is still deep down. So it is fairly impossible to say where an eruption might occur. Some believe that it will happen in the western part of the island, or out at sea south to southwest of the lighthouse. Some believe it will in the end be an eruption closer to land from the vent called Bob, or even on land close to La Restinga.

In the end it is more likely that we will have another Effusive Lava Vent In the Sea, or to put it in short, another ELVIS.

If you are feeling really worried, or things get worse you should read the splendid article on volcano preparedness written by our resident Icelander. More volcano wisdom in that article than anywhere else, a wisdom coming out of extended experience of volcanic eruptions.

http://volcanocafe.wordpress.com/2012/06/29/icelanders-do-prepare-for-eruptions-a-personal-observation/

I would also recommend that if you feel the need to relocate yourself quickly, go to the eastern part of the Island. It should be fairly safe since there has been no activity there. In the light of things, if you are really worried, or things heat up even more, do not wait for an official call for evacuation. Just go if you can or feel the need. Remember that in the end it is you who are responsible for your decisions regarding you and your loved ones.

CARL

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