Graniya: “Gigantic hunks of Ulexite are found in the form of fibrous, compact veins. When polished, these specimens become the well-known “Television Stone” or “TV Stone” sold to amateur collectors. The optical effect exhibited by Television Stone is caused by each of its individual fibers acting as fiber-optic cables, transmitting light from one surface to the other. Since all the fibers are parallel and compacted together, any image at below is transmitted through each crystal fiber to the top surface. For this effect to be seen, the specimen must be polished with smooth surfaces. Fibrous Ulexite bundles can also be carved into cabochons that display strong chatoyancy. However, due to its low hardness, it is unsuitable for gem use.“
Alan C: “Well, ’tis obvious that our Granyia is well read-up on AA Milne! Winnie the Pooh fell into a gorse bush honey hunting gorse is genus Ulex – the prckly subject – so we have Ulexite!! DING!!! Ulexite (NaCa hydroxyborate) – nickname TV Mineral from optics c/f fibre optic cables“
Graniya had not read AA Milne but still got the right answer.
dmf: “Here is the update on the density plotting for El Hierro. Up to the 12th. In this plot the first part shows daily earthquake density with a mesh of 90 x 90 m. For the last days the plot shows the limitation of the system. Too few earthquakes and too much dispersion (see the scale on the right blocked at 0.9) The second part shows a cumulated earthquake density, with a day by day cumulation. Data is from IGN & NOAA, made on Gnu Octave. The second part shows very well the most active areas and the evolution of the quakes focus.“
Still lots more earthquakes as on a regular day in Iceland in the last few months…
El Hierro seems to go dormant at the moment too. There were earthquakes in the region today but not on the places we watched around El Hierro. So most likely normal tectonic earthquakes.
And the run-up time for Etna next ( maybe) paroxysm is probably at least another week.
As for the run-up for Hekla. This is the very best image i have seen so far from the 2013 (possible) eruption:
Tjörnes Fracture Zone is the northern one of the two big fracture zones in Iceland. They connect the northern resp. the southern parts of the rift and there is also a theory about microplates underlying these zones (s. Foulger, etal.).
Bouguer anomaly map showing gravity anomalies of Iceland and its surroundings showing very clearly how it is “embedded” in the MAR, region we are talking about is in the north of the country at the connection of the Arctic part of the MAR; image from Commons Wikimedia
The main geological features in the north of Iceland are this TFZ and the Northern Volcanic Zone which is connected by the TFZ to the Kolbeinsey Ridge, the part of the MAR north of Iceland out in the Arctic Ocean. The Northern Volcanic Zone comprises 5 volcanic systems (from S to N): Kverkfjöll, Askja, Fremrinámur, Krafla and Þeistareykir.
Two, probably even three constituent parts make out this zone from N to S: The Grímsey Oblique Rift (GOR), sometimes also called Grímsey lineament, the Húsavík-Flatey-Fault (HFF) and sometimes there is named a third fault reaching from south of Húsavík over to the Eyjafjarðar Trough, where the last earthquake swarm event took place during the winter. (for a map, see Metzger, p. 422) http://www.n.ethz.ch/~smetzger/download/GJI_2012.pdf )
The now ongoing quake swarm didn’t come as a surprise to the scientists involved, because there has been continuously ongoing research on the region and the newest GPS measurements indicated very strongly a locking at rather shallow depth. This means that plate movements are arrested in a way, and therefore stress builds up – explaining the non-continous rifting events as described eg. by Irpsit. Plates seemingly often move in jumps and bolts and seldom smoothly (silent slip as an exception from the rule).
The locking was found out by analysing eg. seismology, also seismologic history of the region, which has often had heavy quakes in the past (2 magn. 6,5 in 1872), but also last not least GPS. And this is where the newest research comes in. The scientists discovered strong uplift in parts of the TFZ, i.e. in the southeast esp. And that even, after they had taken out by calculation the 2007-8 uplift at the volcanic system of Þeistareykir . While at the same time there was some subsidence in the west, which describes a plate movement to the southeast, meeting some hindrance around the valley of Jökulsá á Fjöllum, the biggest river valley in the region. Such blocking normally is released in considerable quake activity. And that is what is going on at the moment.
Copyright: Icelandic Meteorologic Institute, via RÚV, 03. April 2013
Up to now, there have been 4 big earthquakes and over 700 earthquakes within 3 days at a whole, the map showing the location of the hypocenters of the big ones and the rupture direction. Interesting that three of them have the same rupture direction and that the development is such that there is another center of activity now to the southwest of the first action.
Copyright: IMO by Inge B. (disclaimer: I am just an interested layman, no geologist). Literature:
Th. Thordarson, A. Hoskuldsson: Iceland. Classic Geology in Europe 3. Harpenden 2002, esp. pp.136 …
Some parts (?) of El Hierro experienced a short power outage last night, This was also viewable on the solitary working webcam at the moment which was noticed by some regulars. Quite some earthquakes Mag. 3+ and even some Mag 4+ have been recorded.
chryphia created a new plot which shows the action going on:
Quote:” Here is another 3D plot, no overlays this time . It shows the current swarm and the older earthquakes in two separate color scales. I wanted to see where the central El Golfo bay earthquakes are located exactly: they are slap-bang in the middle of the northernmost, deep (magenta) swarm, barely visible in this plot. This is where all the other swarms originated, thus I am worried that there is even more magma arriving now. For a good 2D view look athttp://www.01.ign.es/ign/resources/volcanologia/html/eventosHierro.html
Earthquake-report.com also used chryphias plot without giving her credit which I personally find absolutely not OK.
Many can explain the current crisis much better than I ever could. So here there are some comments to good to be lost:
GeoLurking says: March 29, 2013 at 04:37
Quote: “when this whole thing was first bopping along, the gov was reticent about doing anything until it became clear that Mag 4.0 quakes were a possibility. Mag 4.0 was where they flinched and it was clear that something could shake loose and hurt somebody, so that was about when they started taking precautions.
One thing that Carl noted was that the seismic gear was probably not set up for volcano monitoring and that IGN and Pevloca had to undergo a paradigm shift from watching for potential landslides to watching for volcanic activity. Outside experts were consulted and new gear was brought in. (the temporary seismic stations and the additional GPS units.)
Now 4.0s seem to be regular fare. It doesn’t lessen the hazard. A 4.0 still releases considerably more energy than a 3.0. For now, the most immediate threat is still the same. Something getting shaken loose from the bluffs.
Then there is how it plays in the volcano scheme of things. If the quakes are being caused by magma forcing it’s way through the rock, the best that I can envision is a series of normal mode faults. A 3.0 has a maximum displacement of 0.275cm. A 4.0 has 1.17cm. That’s would be a crack about 4.3 times the size of the 3.0. Keep in mind that this is probably pushing the Wells-Coppersmith equations a bit outside of what they were intended for, but it does illustrate the differences in the two quake sizes.
If it is magma pushing through rock, what has happened is that the hoop stress of the rock around the area of the magma has been exceeded and the magma breaks open the rock with what is probably a mode 1 crack. This realm of math is beyond me, so I rely on the Wells-Coppersmith crutch to provide some level of understanding. Going whole hog, and looking at the rest of the formula… a normal mode fault of Mag 4.0 has a down dip rupture width of 1.82 km. If intruding magma is what is at play, it could conceivably make a path about half of that width higher each time it happens. If that starts to show up in the quakes…“
Read the whole comment by clicking it.
Renato Rio says: March 29, 2013 at 13:34 Quote: “The PEVOLCA maintains civil protection measures in El Hierro and follows the evolution of the phenomenon 03/29/2013 … 12:38 – Ministry of Economy, Finance and Security * The data indicate that the seismicity has migrated to the southwest in the last 24 hours. The direction of the Civil Protection Plan for Volcanic Risk (PEVOLCA) maintains civil protection measures that were taken last Wednesday in El Hierro given the magnitude of the seismicity that is occurring to the west of the island. As you may recall the steps taken by the management of PEVOLCA are the following: Disabled the lane closest to the on the output side of Frontera tunnel closing the stretch of road between the HI 50 between Cruce de la Tabla and Sabinosa and the access road to the Playa La Madera, the Pozo de la Salud to the confluence with the HI 503. It is important to avoid transit through these areas because of the risk of landslides. Accesses are opened to the Ermida de los Reyes and the southern Sabinar area, HI 400 Meanwhile it is maintained the yellow alert of information to the population in the area bounded by the HI 500 and the height of the Pozo de la Salud to the south, at the confluence of the HI HI 500 with 400 in the crossroads known as El Tomillar. As for the seismo-volcanic phenomena, earthquakes located in the last 24 hours have migrated slightly to the southwest over previous days, reaching the west of Orchilla between 15 and 20 kilometers deep at a distance from the coast between 12 and 15 kilometers. The values of CO2 in the atmosphere have increased but are still within normal parameters. The direction of PEVOLCA wants to remind you that they are doing continuous monitoring and real-time of thr phenomenon, so any change in the pattern of movements that imply risk will be communicated immediately. It also recommends considering the advice of self-protection in the event of earthquakes, known to all, and can be viewed in http://www.gobiernodecanarias.org/dgse/descargas/sismo_hierro/autop_sismo.pdf“
Bruce Stout did some drawings: To understand the images one needs to read Bruce’s comment and all the follow up’s by Peter Cobbold and Bruce. Bruce Stout says: March 29, 2013 at 14:23
Richie Lee gave us a link to a TV station in the Canary islands where some news might be broadcasted. Canary TV: They don’t stream everything but most live newscasts are available. The last few days they have had coverage of the El Hierro activity.
I personally do not think any eruption is imminent, but it is interesting to watch. And in case you need the links again, just holler.
Spica
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A riddle for tonight, while we are watching what is happening in El Hierro and Iceland!
Same as last week …. so link the each clue to a volcano and spot the red herring ….
1 point for each volcano and 1 point for each red herring (with brief explanation)
All solved … Red herrings in bold … Answers ..
No 1 Big Ben
No 2 Mount Churchill
No 3 Hekla
No 4 Glen Coe
No 1 – 2745; Furious 50s; New York landmark; Augustus Pugin; SOLVED
No 2 – Bobsleigh run; Radiocarbon; Battle of Stepney; Infantry Tank; SOLVED
No 3 – 1750; 1104; 1864; 4892; SOLVED
No 4 – 1692; Easter Island; Cauldron subsidence; Harry Potter; SOLVED
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.
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’.
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.)
HEKLA
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.
