[aktueel] Vulkaanuitbarsting bij Canarische Eilanden #3

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Recordaantal aardbevingen op Canarisch eiland

Nog nooit eerder werden er zoveel aardbevingen achter elkaar geregistreerd op het kleine vulkanische eilandje El Hierro, het kleinste van de Canarische Eilanden. De reeks van maar liefst 720 bevinkjes heeft de overheid van deze eilandengroep voor de kust van West Afrika ertoe doen besluiten om voor het eerst in de geschiedenis een vergadering bijeen te roepen van het Stuurcomité van Vulkanische Monitoring. Dit comité werd opgericht om specifieke plannen te realiseren, die de burgerbevolking dienen te beschermen en noodplannen voor vulkanische risico’s moeten ontwikkelen. Inmiddels wordt gesproken over een ‘significante dreiging van seismische activiteit’.

Het Nationaal Geografisch Instituut (IGN) en het Volcanologische Instituut van de Canarische eilanden blijft nauwlettend de aardbevingen in de gaten houden, waarvan de kracht van de bevingen (elke dag!) ligt tussen de 1 en 3 op de Richterschaal. De meerderheid van de bevingen vindt plaats tussen 5 en 15 km diepte.

Volgens de autoriteiten betekent deze seismische activiteit nog niet direct dat een grotere, significante aardbeving zal plaatsvinden. Het merendeel van de bevingen die zijn geregistreerd, vonden plaats in het Noord Westen van het 280 vierkante kilometer kleine eilandje, bij het plaatsje El Golfo (zie foto hieronder). Een aardbeving op deze plaats zorgde er zo’n 50.000 jaar geleden voor, dat er een enorme landverschuiving plaatsvond, waarbij de helft van de vulkaan in zee gleed. Hierdoor ontstond een ca. 100 meter hoge tsunami die naar de overzijde van de Atlantische oceaan zou zijn gegleden. Schuin tegenover dit eilandje, in het verlengde van de resterende halve kratermond, ligt het Noord Amerikaanse continent..

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El Hierro Earthquake Swarm Enters Third Week
The intensity of earthquakes recorded on the smallest of the Canary Islands, El Hierro, has increased slightly during the last 24 hours. However, the total number of earthquakes recorded daily has lessened since the earthquake swarm initially began on 17 July.

The total number of tremors recorded during the past two weeks has now exceeded 1,050, according to the Instituto Geografico Nacional (IGN).

The majority of the earth tremors ranged between 1-2 magnitude, but during the past 24 hours there have been least five tremors measuring in excess of 2.0 magnitude on the Richter Scale. A 2.4 magnitude earthquake was recorded at 4:56 p.m. local time on Sunday (31 July 2011).

Approximately 50 earth tremors were recorded on Sunday, according to local earthquake monitoring agency Actualidad Volcánica de Canarias (AVCAN). The number is slightly down on the number of tremors recorded on Saturday and significantly less than the 195 earthquakes recorded on 22 July.

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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 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 met again on Friday 29 July to discuss the low magnitude seismic activity. It reported that it had stepped up its seismic monitoring operations to identify the source of the earthquakes.

Following an evaluation of seismic and volcanological information gathered by the IGN and volcanological Institute of the Canary Islands, the Committee agreed to activate “monitoring and surveillance mechanisms necessary to coordinate the actions of civilian self-protection and information to people listed in the Plan” (translated from Spanish press release). It remains unclear, however, if the unprecedented seismic activitiy on El Hierro is a precursor to a possible future increase in earthquake or volcanic activity.

Earthquake swarms are events where a local area experiences sequences of many earthquakes striking in a relatively short period of time. The length of time used to define the swarm itself varies, but the United States Geological Survey (USGS) points out that an event may last for days, weeks, or months.

El Hierro’s Volcanic/Seismic Past

El Hierro is situated in the most southwestern extreme of the Canaries. The island was formed after three successive eruptions, and consequent accumulations, the island emerged from the ocean as an imposing triangular pyramid crowned by a volcano more than 2,000 metres high.

The volcanic activity, principally at the convergence of the three ridges, resulted in the continual expansion of the island. A mere 50,000 years ago, as a result of seismic tremors which produced massive landslides, a giant piece of the island cracked off, crashed down into the ocean and scattered along the seabed. This landslide of more than 300km3 gave rise to the impressive amphitheatre of the El Golfo valley and at the same time caused a tsunami that most likely rose over 100 metres high and probably reached as far as the American coast.

Nuevas imágenes de la mancha de emisiones volcánicas en la costa de El Hierro

Material piroclástico en superficie tras la erupción de El Hierro. Día 15-10-2011

Imágenes de la erupción el día 17-10-2011 donde se aprecia el foco principal de la misma

Underwater volcano errupting of coast Canary Islands emits toxic gases

Birth of a new vent on November 23

El volcán de La Restinga, El Hierro.

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NOTE AVCAN 343 - EARTHQUAKE ACTIVITY-VOLCANIC - HIERRO ISLAND - 25 November 2011-10:30 h peninsular - seismic-volcanic activity continues with moderate to high seismicity in the Gulf marine area. According to the PEVOLCA have appeared "quite often a type of volcanic signals (LP). Continued significant volcanic tremor signal in the Restinga area, which remains small amplitude oscillations, more unstable and more explosions, possibly hydromagmatic . the magnitude of the earthquakes between 3.1 and 1.5. New quakes 6. earthquakes senses 1. Depths one to 15, and the rest to 20km. the day before yesterday 21. Yesterday 8. Today van 4. A total of 11,807 earthquakes are located in El Hierro by IGN from 9:00 am of July 19, 2011 (Enrique).

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The truth is that the photos of non-tip / Guardia Civil of the last day November 23, 2011 are beautiful, and one more thing to show us how small is the nucleus of the Restinga, at the foot of a volcanic cone aligned with other more behind and in line with the town, besides the spot next to the town, the thing is close, too much for my taste, so if the picture is very good, is a cover of National Georgraphic so far indicating eruption in el Hierro (Enrique).

Picture of intense volcanic gas discharge by submarine eruptive activity south of the Restinga on the morning of November 23, 2011. Photo: Civil Guard / InVolCan

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Todo se cuadra para la erupción en el norte

The great stain that is leaving the volcano on La Restinga overshadowed on Thursday what is happening in the north of El Hierro, where the location of small tremors in the seismicity and the increase in the rate of CO2 targets shallower magma movements.

The seismicity in the north of El Hierro is decreasing to the point that this Thursday there were only three earthquakes, however, and according to the committee of scientific work to the direction of the Civil Protection Plan for Volcanic Risk (Pevolca) have appeared "quite often a type of volcanic signals (lp) in the Stations of the North Coast." These signals volcanic long period (long period) are equivalent to small tremors associated interrupted movement of magma.

The director of the National Geographic Institute (IGN), María José Blanco, rejected that means full already tremor signal in the north and, therefore, a rash, but admitted that the magma is moving appreciably off the coast . And it does more superficial positions if one looks at it this concatenation of small tremors is linked to a shallower seismicity in recent days in the north, between 15 and 18 kilometers deep.

Furthermore, these two elements adds an increased gas pressure in the magmatic thermal system. The last measurement of the diffuse emission of carbon dioxide (CO2) from the Canary Islands volcanological Institute (Pevolca) on day 20 is around 2,200 tonnes per day (400 tons more than four days before), a value equivalent to 6.34 times the normal average value on the island.

CO2 is the driving force of eruptions, which is why some experts have the feeling that they may be facing an eruptive phase in the north.

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Clouds and transit seismic hypocenters of seismicity to 11/24/2011

Nubes sísmicas de hipocentros y tránsito de la sismicidad al 24-11-2011

Clouds of seismic events and daily traffic of seismicity for seismic-volcanic crisis on the island of El Hierro to 24 November. of 2011

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The diffuse emission of carbon dioxide by the insular volcanic system is already six times the normal average

The diffuse flux measurements of carbon dioxide (CO2) since last July by scientists at the Institute of the Canary Islands volcanological (involcan) at El Hierro reflect an upward trend in their emission into the atmosphere by the volcano island, which is about the 2,200 tons per day. This is a value equivalent to 6.34 times the normal average for the island of El Hierro, which is 345 tons per day.

On the other hand, as reported in a statement, the stain caused by the underwater eruption off the coast of La Restinga has remained widespread in surface and appreciated "some sporadic changes in hue." The sending center has presented a brown color associated with the emission of fine material. On the tremor signal, its amplitude has remained constant and low throughout the day, with some slight increases and no evidence of any second source of tremor . Similarly, with respect to deformation, the results of processing the data obtained with the GPS stations do not reflect any clear trend in the horizontal components other than the regional. Vertically majority view stations and only a collapse of the Gulf seem to point to stability, mainly in the east. Also, the National Geographic Institute (IGN) confirmed the direction of the Civil Protection Plan for Volcanic Risk (Pevolca), that during this eight earthquakes were located Thursday, with only one of them felt by the population, with an intensity of II. Most of these events are located in the Gulf, aligned in the northeast-southwest in the sea at a depth between 15 and 24 kilometers. The more intense, with a magnitude of 2.8 on the Richter scale, had place at 20:54 hours west of La Frontera at a depth of 16 kilometers. In total, since the day July 17, 2011 11 832 earthquakes have been located.

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The evolution curve of the cumulative seismic energy released looks set moderating its rise, releasing less and less energy.

This may be because the system is relaxing or on the contrary it has been re-hitches and a few days ago, since it is still early to rely, as the last time you did this, ended with a 4.6, Will this in the coming days? or else I still relax, releasing less and less energy?

We'll see what happens, but seeing the gases and the deformation does not seem to be relaxed, especially gases (Enrique)
[bron]

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Update 26/11 – 12:42
The best you can do at the moment is staring at our webcam. For minutes in a row, we have seen periods of smoking magma. The smoking magma was first seen by reader Hans-Werner who also captured the image on his screen. Hans-Werner has told us also that the webcam was operated in the right direction when it happened. This is also great news to hear as the webcam operators seem to have learned from past critics.


Update 26/11 11:30
Joke reports that her friend, the La Restinga human webcam, has growing fear that a new evacuation is not far away as the stain is very visible from the village this morning (Ian reported the same in his 09:52 update). She thinks that if the wind eventually changes, La Restinga might be in the center of the storm again.
Update 26/11 11:28
- The volcanic earthquakes have picked up their daily work again. Since 09:21 this morning 4 M+1.5 earthquakes have been listed by IGN, the strongest one being a M 2.7 earthquake NW of Frontera
Update 26/11 09:52 Ian Carson reports :
A lot of stain right to coast at La Restinga but no emission points can be seen by me. I don't think the earlier mention of a closer one was true. Harmonic calm.
Update 26/11 09:43
- 3 earthquakes have occurred since midnight, all of them less than 1.5, the reason why these quakes are not listed in the IGN main list. 2 of these quakes had a depth of 14.8 km
- while looking at the webcam for a longer period a lot of mysteries are showing up. Here are a few of them :
- why can toppling waves almost only be spotted in the stain waters ?
- why do we have sudden color change in parts of the stain ?
Update 26/11 09:05
- the beautiful calm Las Calmas sea enables us this morning to trace the eruption vent. The arrow on the picture below is the location were we expect that the vent is (probably) degassing. About 15 to 30 minutes ago, we have spotted here the source of a white stain. Unfortunetely the Telefonica operators have since zoomed more to the left . The Telefonica operators have since zoomed the image and probable stirring action has to be located at the upper right corner.

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Data Update 26/11 – 23:42
- A lot of action in the sea means mostly a limited number of earthquakes. Today only 8.
- Depth in between 14.8 and 20.3 km
- Medium harmonic tremor with a limited number of bursts

Ian Carson reports from El Hierro :
I went to La Restinga at first light to see any overnight developments - there weren't any - just the usual stain a bit closer to the shore. After an hour and as it was lovely morning, I went sightseeing. I was returning to La Restigna when I got the message of smoking lava stones.
When I arrived there were little 'bombs coming to the surface intermittently. These got more frequent for a while and then only one every 5 mins. After a while the activity again increased, bright Jacuzzi and many stones coming up, generally smaller than the first batch. Stones were visible on the surface. The affected area seemed to be getting larger and the activity seemed quite intense when I had to leave at 17.40. I look forward to first light ! The Ian Carson images are included in the group below. Click on the image to watch the entire group of pictures.

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Data Update 27/11 – 09:14
The activity at the eruption area gets even stronger than before. The webcam operator just zoomed out a little to have a wider scoop. Earthquake-report.com expects more action today. A stronger Jacuzzi and from time to time a swelling geyser type action.

Data Update 27/11 – 08:50
The coast guard boat on the image will have the best pictures. What he does is however very risky as nobody can predict the start of a subaerial phase of the eruption.

Data Update 27/11 – 08:09
- the action which started yesterday by floating smoking stones is continuing this morning, hot pyroclastic material is floating to the surface. Just behind a weak Jacuzzi is formed. All this can be seen on the Telefonica eruption webcam.

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NOTE AVCAN 346 - EARTHQUAKE ACTIVITY-VOLCANIC - HIERRO ISLAND - 26 November 2011-21:30 h peninsular - seismic-volcanic activity continues with moderate to high seismicity in the Gulf marine area. Continue an important sign of volcanic tremor in the Restinga area, which is maintained in amplitude with increasing trend (10%) since the last note, with small oscillations and some explosions, possibly hydromagmatic (by the way the pattern has repeated explosions every 3 hours approx). The magnitude of the earthquakes between 2.2 and 1.5. New earthquakes 4. Depths to 17, 19, 19 and 20km. Before yesterday 8. Yesterday 10. Now go 8. A total of 11,821 earthquakes are located in El Hierro by IGN from 9:00 am of July 19, 2011 (Enrique).

NOTE AVCAN 347 - EARTHQUAKE ACTIVITY-VOLCANIC - HIERRO ISLAND - 27 November 2011-11:15 h peninsular - seismic-volcanic activity continues to moderate, with seismicity in the Gulf marine area. Continue an important sign of volcanic tremor in the Restinga area, which is maintained in amplitude with the low tendency (5-10%) since the last note, with small oscillations, and more unstable, with some explosions, possibly hydromagmatic (indeed the pattern of repeated explosions every 3h approx). The magnitude of the earthquakes between 2.3 and 1.1. New earthquakes 11. 17 and 20km depth (and two at 2 and 14km and three to 21, 22 and 25km). The day before yesterday 10. Yesterday 9. Today are 10. A total of 11,832 earthquakes are located in El Hierro by IGN from 9:00 am of July 19, 2011 (Enrique).

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Data Update 28/11 – 10:01 – Ian Carson reports
Just had long chat with scientists. Depth of vent yesterday was imprecise according to the captain. Now the real news, a new scientific ocean survey ship is coming tomorrow to map the area. It will also do work in the north (El Golfo region).

Data Update 28/11 08:33
- Harmonic tremor remained strong all night
- Contrary to yesterday, no smoking stones this morning. We have just watched a time lapsed period since the beginning of daylight and no surface activity has been noticed on the webcam
- Ian Carson reports that the usual stain is visible but no stirring activity
- 3 earthquakes since midnight, the strongest one being a M 2.0
- depths in between 17 and 21 km
- weather outlook for today : beautiful weather today, wind blowing from the east, maximum wave height : 0.6 meter, wind speed : 1 to 2 knots only in other words a perfect day for volcano activity spotting