Geologists on Canary Islands commence study on El Hierro swarm of 6000 quakes

September 15, 2011CANARY ISLANDS – The Canary Islands Government says it has commenced an in-depth geological survey of El Hierro, the smallest of the islands, in an effort to determine the source of an earthquake swarm. The unprecedented seismic activity commenced on 19 July. In excess of 6,000 earthquakes have been recorded up to 14 September 2011. More than two dozen tremors were recorded during Wednesday (14 Sept.) alone. The vast majority of the tremors have been recorded in the northwest of the 278.5-square-kilometre island at El Golfo, the location of a massive landslide that created a 100-metre high tsunami almost 50,000 years ago. The earth tremors have ranged between 1 and 3 magnitude, the National Geographic Institute (IGN) reported. However, the Volcanological Institute of the Canary Islands and Actualidad Volcánica de Canarias have both reported a sizeable decrease in the number of tremors recorded during the first two weeks of September, compared to the latter half of August. The National Geographic Institute confirmed on Wednesday that it has commenced a geological study of the epicentre of the tremors in the town of Frontera. Local officials admitted that the origin of the seismic movements could be volcanic, but further examination is required. The Council of Hierro noted that there is no imminent threat to the residents of the sparsely populated island (10600 inhabitants), but refused to rule out an evacuation of island residents in the event of a heightened risk of a volcanic eruption. The earthquake swarm, prompted the Canary Islands Government to convene the first ever meeting on 22 July of the Steering Committee and Volcanic Monitoring, reflected in the Specific Plan Protection Civil and Emergency for Volcanic Risk, given what it described “the significant increase in seismic activity.” The Committee has met numerous times since then to discuss the low magnitude seismic activity. It reported on Monday that it had stepped up its seismic monitoring operations to identify the source of the earthquakes. It remains unclear if the unprecedented seismic activity on El Hierro is a precursor to a possible future increase in earthquake or volcanic activity.  However, the latest surge in recorded earthquakes and the inflation of the volcano could indicate magma rising underneath El Hierro. –IWO
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7 Responses to Geologists on Canary Islands commence study on El Hierro swarm of 6000 quakes

  1. luisport says:

    This week’s Global Volcanism Program Weekly Volcanic Activity Report from the Smithsonian Institute and the USGS is a little busier than previous weeks, so let’s check out some highlights:

    Canary Islands: For the first time this year, the seismicity at El Hierro has made the report. The volcano, as many of you know, has been experiencing increased seismicity since June, with over 6,200 earthquakes thus far, along with increased carbon dioxide emissions as well. However, beyond this there have been little in the way of other signs that an eruption in coming soon – AVCAN (Actualidad Volcánica de Canarias) still has El Hierro on green alert status, even with all this seismicity.

    Indonesia: We can add Ranakah on Flores Island in Indonesia as another volcano to watch. Ranakah is a dome complex that most recently saw a VEI 3 eruption in 1987 when the youngest dome was formed. Right now, small steam plumes and increased seismicity have prompted the PVMBG to raise the alert status to 2. Ranakah isn’t the only Indonesian volcano to see its alert status go up, as Tambora was raised to alert status 3 after continued rumbling – preparations for possible evacuations are underway by the Regional Disaster Mitigation Agency (BPBD) of West Nusa Tenggara. Even Merapi has been puffing away, producing diffuse ash plumes along with GVP Report regular Dukono. Finally, Soputan, saw a marked decrease in activity so the alert status there was lowered to 2.

    http://bigthink.com/ideas/40208

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  2. I don’t get it. From what I have seen and read, it appears obvious that they are volcanic in origin??? On Eruptions blog, “lurking” has mapped all the epicenter points, and it seems rather obvious from his findings that the magma chamber can be clearly seen in his diagrams. Any comment on this Alvin?

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    • It’s definitely magmatic. Both the Canary Islands and Azores sit over magma plumes. If 6000 earthquakes erupted in Yellowstone, an intraplate magma plume, over a 8 week period in the U.S.- there would be mass panic.

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    • luisport says:

      Lurking on September 16, 2011, 3:48 AM
      Meh.

      El Hierro Six hour Quake Count 7/15/2011 to present.

      Inflation data isn’t readily available… and I don’t have a handle on the “Mogi” model anyway. What is available are variations in separation among a few stations in the Canaries.

      http://www.01.ign.es/ign/resources/volcanologia/deformacion.html

      You could try to derive an x and y offset from the data by working with the data, and then try to shoe horn it into a guestimate from the Mogi model, but that’s above me and a bit tedious for getting a ball park estimate of potential eruptive volume.

      So… I took a semi-educated guess to come up with my estimate of what is available should it go, based on what data we do have.

      Assumption #1 – The quakes define the area of fresh magma. This may not be accurate, and the main body of magma could lie just below where the quakes are at, with the quakes being nothing but dike emplacements.

      Assumption #2 – Some percentage of the rock in the quake area contains eruptible material. (this is a big variable and drastically affects my estimate)

      Assumption #3 – That the Normal distribution accurately describes the structure. With 5830 individual quakes, I at least hope that it’s close.

      The first thing I did was to find out what the three radii were for an ellipsoid based on the distribution of the quakes. For the latitude and longitude, I converted the standard deviation to meters. (stdev for depth was also converted to meters).

      According the the Normal Distribution, 68.26% of the members lie within one standard deviation (sd) of the mean. 95.44% lie within two sd.

      Finding that volume and then making a guess (Assumption #2) gives you the following data.

      Standard caveat, I am not a geologist and this is just a guestimation by an amateur.

      Your guess/estimate may be better. If you can find the needed data and can gnaw your way through the equations, here is a link to the Mogi Model (that I did not use but it supposed to be pretty good)

      http://www.geophys.uni-stuttgart.de/oldwww/ew/volcano/node8.html

      http://www.pressan.is/frettir/lesafrett/jardvisindamenn-uggandi-naesta-eldgos–i-krysuvik-land-ris-og-vatnsyfirbord-i-kleifarvatni-laekkar

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  3. luisport says:

    Peter Tibben on September 16, 2011, 6:41 AM
    @ Erik and all
    I follow news of the Canary Islands with special interest. therefore
    I posted some pictures of El Hierro in my Picasa webalbum. And a few other things which might interest you.

    https://picasaweb.google.com/103122365692586389301/ElHierro?authkey=Gv1sRgCLjCnc_b2pi4KQ#5652886273657266466

    For more information on El Hierro and the other Canary Islands I recommend Classic Geology in Europe, Canary Islands, its a musthave for anyone visiting the Canaries for its geology and volcanoes. It is still available at Amazon:

    http://www.amazon.com/Canary-Islands-Classic-Geology-Europe/dp/1903544076/ref=sr_1_3?s=books&ie=UTF8&qid=1316167178&sr=1-3

    On October 23 it is exactly 40 years ago that the latest eruption took place in the Canaries. On La Palma the Teneguia cone was build. A report of the eruption can be viewed on the Global Volcanism web page:

    http://www.volcano.si.edu/world/volcano.cfm?vnum=1803-01-&volpage=var

    I posted an excerpt of a dvd of the eruption on YouTube, the narrator first mentions the 1866 eruption, but the footage is from 1971:

    A lot of links to keep you busy.

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  4. Dominic says:

    Can anyone shed any light??
    I had a report that El Hierro had a small eruption a week or so ago and can not find any info on this anywhere.. Bull or true? Anyone know…

    Cheers,
    Dom

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