quote: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..
quote: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.
quote: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.
quote:The Swarm of earthquakes which started during July of 2011 have continued into August with 3277 earthquakes being recorded since August 1st 2011 until 23rd August 2011, this is a significant rise of earthquakes and has Experts keeping a close eye on the island.
The news may have lost interest when the swarm started in early July with over 1300 earthquakes being recorded for the month which was a huge increase in activity compared to the average 300 micro-quakes the area experiences a month.
But burying these facts wont make it go away, as figures and records show it is getting much worse with already 3277 Earthquakes being recorded in just the past 23 days. These are the figures that should cover the whole YEAR not 23 DAYS.
2010 the area registered 3661 earthquakes for the year.
2009 the area registered 4536 earthquakes for the year.
2008 the area registered 5158 earthquakes for the year.
2007 the area registered 5384 earthquakes for the year.
2006 the area registered 3689 earthquakes for the year.
2005 the area registered 4229 earthquakes for the year.
For 2011 the total stands at 6614, of which 4617 have happened in just the past 7 weeks.
2010 eruptions of Eyjafjallajökull saw thousands of Micro-quakes prior to the Eruption of this volcano.
(A microearthquake (or microquake) is a very low intensity earthquake which is usually three or less on the Richter scale. Microquakes occur often near volcanoes as they approach an eruption, and frequently in certain regions exploited for geothermal energy)
El Hierro Volcano: Is one of the Smallest of the Canary Islands, the origins of the Island date back some 100 million years when the Ocean floor shifted with the movement of the Earth's mantle. The crust cracked into a three pointed star releasing flows of Magma.
After 3 Eruptions, the island emerged from the ocean as an imposing volcano more than 2,000 Meters high.
It has now been over 200 years since the last Eruption but El Hierro although being the smallest Island has the Largest number of Volcanoes with over 500 open Sky Cones and another 300 covered by the most recent outflows.
There has been uncertainty surrounding reports of a historical eruption taking place in 1793.
Ditquote:Op woensdag 24 augustus 2011 12:34 schreef spijkerbroek het volgende:
Hmm zat ik net te kijken of ik in m'n vakantie in oktober naar de Canarische Eilanden wil, lees ik dit topic.. toch nog maar ff goed over nadenken
Tevens is de TT fout. Gran Canaria =/= El Hierro
--------------------------------------------------------------------------------quote:More than 1,000 calls were made to the emergency number after the quake on the south east of the island. There was no damage or injuries. The 112 emergency number on the Canary Islands received more than 1,000 calls from concerned members of the public after an earthquake in Agüimes, on the south east of Gran Canaria, on Monday afternoon. None reported any injury or damage to property however. The quake at 2.15 pm was a 3.4 magnitude on the Richter scale, with the epicentre at sea off the coast of Playa del Inglés. Its effects were also felt in Santa Brígida, Telde, La Aldea de San Nicolás and Santa Lucía de Tirajana. There was a small tremor on El Hierro earlier on Monday, where EFE notes more than 3,700 seismic movements have been detected since July 19 this year.
Ja die 3.4 quake was een andere dan de zwerm bij El Hierroquote:Op woensdag 24 augustus 2011 12:51 schreef zenkelly het volgende:
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Zowel het eilandje El Hierro, maar sinds maandag ook Gran Canaria zelf, dus. Ik heb het idee, dat het hier om 2 verschillende epi-centra gaat?
quote:Op woensdag 24 augustus 2011 12:38 schreef Anakin24 het volgende:
Als ik er zo naar kijk heb ik mijn vermoedens over een "boem" die daar gaat plaatsvinden
Iets met een magmakamer die zich fijn aan het vullen is...
tja en we kunnen er niks aan doen
MMMmmm(agma)... afwachten...quote:Magma under El Hierro building up?
Well, we've been wondering when we might see more signs of magma rising underneath El Hierro in the Canary Island and now we seem to have got some. Over the last month, the island/volcano has experienced thousands of earthquakes that have waxed and waned in number, but seem to be increasing over time. A GPS survey of the area effected by the earthquakes has now found deformation - namely inflation - over part of the volcano. This inflation is on the order of ~1 cm over the last 20-25 days according to the Instituto Volcanologico de Canarias. There are also slightly increased carbon dioxide and temperature (above background) at the volcano as well. All of these signs add to up new magma rising in the volcano -
So the big question becomes "does this mean an eruption is around the corner?" Well, my answer to that is a resounding "maybe". Sure, these are all signs of magma emplacement, but there is likely as much chance of it all "stalling" in the crust as an eruption occurring. It will be how these factors - earthquakes, deformation, gas emissions, temperature - change over the next weeks to months that will give us a better idea of whether we will see the first documented eruption at El Hierro since 550 B.C. (or 1793 A.D., depends on if you trust the historical reports from the late 18th century).
Ik zat al te denken van "zitten daar geen vulkanen?" Dat zou idd ook nog wel eens de oorzaak kunnen zijn.quote:
Vind je, er zijn af toe nog wel kleine clusters van bevingen: http://www.avcan.org/index.php?m=Mapas&a=mapa&mf=53quote:
Eerste keer dat ElHierro nu genoemd wordt op deze sitequote:El Hierro: 6200 seismic events until 7 September
The Spanish Geographic Institute (IGN) reported that since 16 July, seismicity at Hierro was high above the background levels. Until 7 September more than 6,200 events had been located, most of them in the El Golfo area with hypocenters that were 10 km deep, all magnitudes were below 3. The seismic activity alternated between relatively calm periods and high-energy periods. GPS local network stations showed deformations of about 2 cm. High rates of carbon dioxide flux were measured in the anomalous area.
Geologic Summary.
The triangular island of Hierro is the SW-most and least studied of the Canary Islands. The massive Hierro shield volcano is truncated by a large NW-facing escarpment formed as a result of gravitational collapse of El Golfo volcano about 130,000 years ago. The steep-sided 1500-m-high scarp towers above a low lava platform bordering 12-km-wide El Golfo Bay, and three other large submarine landslide deposits occur to the SW and SE. Three prominent rifts oriented NW, NE, and south at 120 degree angles form prominent topographic ridges. The subaerial portion of the volcano consists of flat-lying Quaternary basaltic and trachybasaltic lava flows and tuffs capped by numerous young cinder cones and lava flows. Holocene cones and flows are found both on the outer flanks and in the El Golfo depression. Hierro contains the greatest concentration of young vents in the Canary Islands. Uncertainty surrounds the report of an historical eruption in 1793.
en als we niks meer van je horen dan zullen we op je leuke tijd hier drinkenquote:Op donderdag 25 augustus 2011 13:38 schreef Keiichi het volgende:
Over 3 weken ben ik daar in de buurt, ik zal wel even gaan kijken
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