2011 El Hierro eruption
Encyclopedia
The 2011 El Hierro eruption is an on-going volcanic
event just off the island of El Hierro
, the smallest and farthest south and west of the Canary Islands
(an Autonomous Community
of Spain
), in the Atlantic Ocean
off the coast of Africa
. As of 25 November 2011 the eruption is underwater
, with vents located approximately 2km to the south of the fishing village of La Restinga on the southern coast of the island.
’s seismic monitoring station located in Valverde
. The seismic monitoring network was increased in density on 21 July to allow better detection and location of the seismic events. There was an earthquake swarm
with in excess of 400 minor tremors
between 20 July and 24 July; by
27 July a further 320 earthquakes had been recorded. On 25 August there were reports that some horizontal deformation had been detected, but that there was no unusual vertical deformation. At that time, the total number of tremors had exceeded 4000. By the end of September, the tremors had increased in frequency and intensity, with experts fearing landslides affecting the town of La Frontera
, and also a small possibility of a volcanic eruption through a new vent. In late September emergency services evacuated several families in the areas at most risk, and made plans to evacuate the island if necessary.
. Harmonic tremors are produced by magma
movements and can indicate that an eruption has begun. It was thought that a small submarine eruption may have begun, 2km south of La Restinga.
In early November the 600 residents of La Restinga were evacuated for the second time. A confirmed surtseyan
type of eruption phase started at the fissure on 7 November 2011. On 25 November 2011 the eruption was ongoing with vigorous phreatic bubbles emerging.
Three webcams in La Restinga have been focussed on the 'stain', the area of the sea under which the eruption is taking place.
The main volcano on the island, Tanganasoga, is currently undergoing rapid inflation and increased carbon dioxide
gas emissions, which are a cause for concern. On 24 November there were various report of a sulphorous smell in the El Golfo area of the island.
The eruption is currently ongoing. On 27 November the coast guard vessel Salvamar Adhara collected a 'floating lava bomb', one of many that had been ejected by the underwater eruption and floated to the surface of the sea.
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...
event just off the island of El Hierro
El Hierro
El Hierro, nicknamed Isla del Meridiano , is the smallest and farthest south and west of the Canary Islands , in the Atlantic Ocean off the coast of Africa, with a population of 10,162 .- Name :The name El Hierro, although phonetically identical to the Spanish word for 'iron', is generally thought...
, the smallest and farthest south and west of the Canary Islands
Canary Islands
The Canary Islands , also known as the Canaries , is a Spanish archipelago located just off the northwest coast of mainland Africa, 100 km west of the border between Morocco and the Western Sahara. The Canaries are a Spanish autonomous community and an outermost region of the European Union...
(an Autonomous Community
Autonomous communities of Spain
An autonomous community In other languages of Spain:*Catalan/Valencian .*Galician .*Basque . The second article of the constitution recognizes the rights of "nationalities and regions" to self-government and declares the "indissoluble unity of the Spanish nation".Political power in Spain is...
of Spain
Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...
), in the Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
off the coast of Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
. As of 25 November 2011 the eruption is underwater
Submarine volcano
Submarine volcanoes are underwater fissures in the Earth's surface from which magma can erupt. They are estimated to account for 75% of annual magma output. The vast majority are located near areas of tectonic plate movement, known as ocean ridges...
, with vents located approximately 2km to the south of the fishing village of La Restinga on the southern coast of the island.
Earthquakes
Beginning on 17 July 2011, increased seismic activity was detected by the Instituto Vulcanológico de Canarias (Volcanological Institute of the Canary Islands) and National Geographic InstituteInstituto Geográfico Nacional (Spain)
The Instituto Geográfico Nacional , or National Geographic Institute is a Spanish government agency, dependent on the Spanish Ministry of Public Works...
’s seismic monitoring station located in Valverde
Valverde
Valverde is a province of the Dominican Republic. It was split from Santiago Province in 1958.-Municipalities and municipal districts:The province as of June 20, 2006 is divided into the following municipalities and municipal districts and the municipal Seat within them:* Santa Cruz de Mao, head...
. The seismic monitoring network was increased in density on 21 July to allow better detection and location of the seismic events. There was an earthquake swarm
Earthquake swarm
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 points out that an event may be on the order of days, weeks, or...
with in excess of 400 minor tremors
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
between 20 July and 24 July; by
27 July a further 320 earthquakes had been recorded. On 25 August there were reports that some horizontal deformation had been detected, but that there was no unusual vertical deformation. At that time, the total number of tremors had exceeded 4000. By the end of September, the tremors had increased in frequency and intensity, with experts fearing landslides affecting the town of La Frontera
Frontera, Santa Cruz de Tenerife
La Frontera is the westernmost municipality in El Hierro, Santa Cruz de Tenerife and the Canary Islands, Spain. It is situated on the western coast of El Hierro. Until 2007, Frontera was one of the two municipalities in population that was larger than the island capital...
, and also a small possibility of a volcanic eruption through a new vent. In late September emergency services evacuated several families in the areas at most risk, and made plans to evacuate the island if necessary.
Eruption
Between 4.15 and 4.20am on 10 October 2011 the earthquake swarm changed behaviour and produced a harmonic tremorHarmonic tremor
Harmonic tremor describes a long-duration release of seismic energy, with distinct spectral lines, that often precedes or accompanies a volcanic eruption...
. Harmonic tremors are produced by magma
Magma
Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...
movements and can indicate that an eruption has begun. It was thought that a small submarine eruption may have begun, 2km south of La Restinga.
In early November the 600 residents of La Restinga were evacuated for the second time. A confirmed surtseyan
Surtseyan eruption
A Surtseyan eruption is a type of volcanic eruption that takes place in shallow seas or lakes. It is named after the island of Surtsey off the southern coast of Iceland....
type of eruption phase started at the fissure on 7 November 2011. On 25 November 2011 the eruption was ongoing with vigorous phreatic bubbles emerging.
Three webcams in La Restinga have been focussed on the 'stain', the area of the sea under which the eruption is taking place.
The main volcano on the island, Tanganasoga, is currently undergoing rapid inflation and increased carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
gas emissions, which are a cause for concern. On 24 November there were various report of a sulphorous smell in the El Golfo area of the island.
The eruption is currently ongoing. On 27 November the coast guard vessel Salvamar Adhara collected a 'floating lava bomb', one of many that had been ejected by the underwater eruption and floated to the surface of the sea.
External links
- Daily updated webpage on the eruption
- Photo of the floating lava bombs on 27 November
- Instituto Vulcanológico de Canarias page with many photos (in Spanish)
- 4D model of earthquake swarm July to September 2011
- Global Volcanism Program, Smithsonian Institute
- Daily Mail article with photographs
- James M. Day, e.a.: Evidence for distinct proportions of subducted oceanic crust and lithosphere in HIMU-type mantle beneath El Hierro and La Palma, Canary Islands, 2010 (Science Direct, PDF)
- Martin J.R. Gee, e.a.: Landslides and evolution of El Hierro in the Canary Islands, Marine Geology 177 (2001), 271-93 (PDF)
- M. R. Gee, e.a.: Offshore continuation of volcanic rift zones, El Hierro, Canary Islands, Journal of Volcanology and Geothermal Research, 105 (2001), 107 - 119 (PDF)
- F.G. MONTESINOS: New study of the local gravity field of El Hierro (Canary Islands), Física de la Tierra, 2005, 17, 113-127 (PDF)
- Longpre, M.; Troll, V.; Hansteen, T. H.; Anderson, E.: Ankaramitic Lavas and Clinopyroxene Megacrysts From the Tanganasoga Volcano, El Hierro Island (Canary Archipelago), American Geophysical Union, Fall Meeting 2009, abstract #V51A-1662, Publication Date: 12/2009 (Abstract)
- N. A. Stroncik, e.a.: The magmatic plumbing system beneath El Hierro (Canary Islands): constraints from phenocrysts and naturally quenched basaltic glasses in submarine rocks, Contrib Mineral Petrol (2009) 157:593–607, DOI 10.1007/s00410-008-0354-5 (PDF)
- J. J. Hernandez, e.a.: Volcanic caves in El Hierro island, Canary Islands, Spain (PDF)
- J. de Nuez Pestana, e.a.: Geology and volcanology of La Palma and El Hierro, western Canaries , Estudios geológicos, Vol. 57 no.56, 175-273 (Abstract)
- Serie Sísmica de El Hierro, Grúpo de Investigación de Ingeniería Sísmica, Universidad de Madrid , act. 29.9.2011 (Spanish)