El Hierro’s western part on “Code Yellow”.

Pevolca reacted on the earthquake series that happened yesterday and set the western part of the island to a “yellow alert zone”. All this happened in agreement with the government of El Hierro.

The dramatic events on CHIE yesterday.

The dramatic events on CHIE yesterday.

Full report (in spanish) and a short excerpt for your information: Closing the lane of the tunnel closest to the exit in Frontera, closing the length of road HI-50 between ‘Cruce de La Tabla’ and ‘Sabinosa’ and the access road to ‘Playa La Madera’, of ‘Pozo de la Salud’ until the crossing with road HI-503.

Yellow informative alert for the population at the zones limited by HI-500 at ‘Pozo de la Salud’ to the South, en the crossing between HI-500 with HI-400 at the crossing known as ‘El Tomillar’.

The best sites to get the newest information are:

Those 2 sites are not normal blogs like VolcanoCafe publishing a full post every few days but they report close to the “action”.

dfm created a brilliant plot and explained it:

This is the update till 18h43 today

Today there were a number of strong (for El Hierro) earthquakes with quite a few over mag 4 which is quite rare.

In the list of earthquakes you will notice that for the strongest earthquakes there is only one event of similar magnitude (4.6) and that in all the events with mag >=4 (16 out of more than 17000 !) 5 came to happen today.

(The ful list of quakes dfm used can be found in his comment on “Watching Hekla“: dfm says: March 27, 2013 at 21:15 )

Without wanting to be fear mongering, I find this situation unprecedented. If you add this to an also unprecedented trend in the upward component of the GPS, this situation begins to pose a number of questions. Happily (if one may say) the bulk of the seismicity is located at sea and not on the island emerged part.

Meanwhile here is the earthquake update for the period since March 26th 8h18 and 27th @ 18h43. It includes the 4.6 quake.

The color of the quakes is linked to their position on the list (more than 1200 events since March 18th).
I will probably change this next time as the color scale loses its interest.

It is interesting to note in the time-lapse animation that there are first some cluster of quakes in the previous parts, leading to a hypothesis of a “sill” of sorts or at least to an accumulation of rock breaking in the same place. Then most of the “strong” (meaning over Mag 3 ) quakes seem to appear on the border of that cluster (look at 0’20”). Could it be that there was some renewal of magma arrival (a new “bolus”) and that the constraints bring some rock breaking on the limit of the previous cluster. I will only repeat that these new events happen in a zone previously devoid of earthquakes.

The 4.6 event can be well see at 00’49” on the center-left part of the plot, over the 27,6 mark on the abscesses.

Do look at the end of the video in the zoom sequence (1’22” and 1’28”)

On the right side of the colorbar the terrain elevation scale is shown. Magnitude of the events (sorry I stopped at 4 !) is shown on the lower part of the plot.

Data from IGN and NOAA, made on Gnu Octave.

Peter Cobbold noted: Bearing in mind the GPS stations are ~15km away from the swarm centre the 100mm uplift in ten days is unusually high for Hierro. Previous swarms have been co-located with the GPS stations and resulted in smaller uplifts over longer periods,IIRC.

Yesterdays trend. El Nathan did not really see a tendency of the earthquakes coming closer to the island.

In case more earthquake swarms happen, there is the possibility of rockfall (or maybe even landslides). At the very moment an eruption on the island is unlikely in my eyes. (Personal layman opinion.)

Links to watch El Hierro (besides the cams) are to be found on Wonder what Bob is up to.

Lets not forget some here like Jamie and Islander are still on a 24hr Hekla watch.
Hekla is still on alert level yellow but not all too much happened close to it yesterday.
Islander also informed us:
Hekla “news service” latest scoop : IMO has brought back online the fourth (4) SIL for monitoring the greater Hekla area. These are HAU from the west, fedgar. (http://hraun.vedur.is/ja/oroi/fed.gif) from the north, VAT from the east and MJO from the south. Nothing EQ wise then can escape the sharp eyes of the IMO staff. http://hraun.vedur.is/ja/oroi/index.html
Fedgar is not on this overall map.

Again the Hekla links:


Other sites have the information about the earthquakes too but dfm’s plot is only on VC.


507 thoughts on “El Hierro’s western part on “Code Yellow”.

  1. Question for the chemists (posed above already but in danger of getting lost). I know sedimentary rock only gets into serious metamorphosis at great depth (something like 700 km for gneiss if I remember correctly) but is it possible that the heat from the plume plus the weight of the edifice could have altered the sedimentary layer sandwiched between the crust and the island? And if so, does this have any implications for magma transport/ fault propagation?

    • You can also have contact metamophism when there is a magmatic intrusion. This should be what we have at El Hierro. As to its effects on magma transport, your advice is as good as mine…..

      • Cheers! thanks dfm. I was wondering if this explains why the swarms are constrained in the oceanic crust and seem unable to penetrate the sedimentary layer.

    • Foliated intermediate species will tend to occur. Shale, Phylite, Schist, Gneiss…. in abouut that order. From pressure vs depths calcs from a while back, I estimate that phyllite is roughly what would be most likely. (in the Jurassic era sediment)

  2. Website is accessible again, seems no HT or something, so it seems we don’t have a winner but clearly a runner up…

      • As far as I remember, it never went over 4,3 up to now. But they had thousands of quakes in the whole, a lot of them over 3 and felt by the population. :(:

        • It must be absolutely terrifying for the poor people there: stronger quakes and coming thick and fast.

          • Earthquake of magnitude 4,6 as reported by IGN:
            11/11/2011 00:20:16
            27/03/2013 15:07:56
            29/03/2013 08:14:44

  3. Pingback: EL Hierro still going strong and a riddle | volcanocafe

  4. Today is now officially the busiest day in the history of VolcanoCafe 🙂 never before have we seen this much pageviews and visitors!

    A very big thanks to all commenters for making this place such a lively place! And also thanks to all Dragons for providing the posts and keeping the dungeons clean!

  5. Pingback: Rockfall at El Hierro after M4.9 Earthquake – 31st March 2013 | Family Survival Protocol

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