Characteristics and possible evolution of the eruption in El Hierro

On this island, a volcanic eruption occurs fissure and surtseyana type. The volcanic materials could be found taquilitas.

Underwater volcanic eruption continues off the coast of South El Hierro. Eruptive focus closer to the surface of the sea it was located about 150 meters deep. The result of the shallowness on Saturday October 15 began to see the first magmatic material at the sea surface, but stopped a few days after coming to the surface, presumably because the eruptive mouth closed.

The eruption of El Hierro launched at sea pyroclastic

These pyroclastic materials collected by the ships that have come to the point eruption and even coastal areas south of the island rocks are composed of two distinct visually.

Characteristics of the materials recovered from the eruption magmatic

These pyroclasts were formed out of lava 150 meters deep and 2.4 kilometers from the coast El Hierro. On the outside are black and round or oval shaped, but inside is a white, porous material, full of gas bubbles formed by the magma dragged from deeper zones.
The dark material is, according to a preliminary study of non-tip, a taquilita. This type of rock is a volcanic glass formed after rapid cooling of basaltic magma. As for the white material needed more comprehensive analysis.

What kind of volcanic eruption is El Hierro

In addition, the volcanic eruption of El Hierro is fissural type, which means that the lava does go outside along a fracture that can break the surface along a fissure or opening several more or less aligned mouths .

And that is the underwater eruption that takes place on the island of El Hierro appears to have several sources. According to official information would be at least three places that have gone lava and gases.

The lava eruptions of this type of flow with relative ease, ie that are not highly viscous lavas and are not in their composition a high percentage of silica. Basic lavas would.

Surtseyana eruption in El Hierro, the four phases

Also described the surtseyana like rash, by the eruption of Surtsey Island in Iceland. However, in this case the name refers to a volcanic eruption under water near the sea surface and this name affect the eruptive mouths found in shallower waters. The deeper pockets of the underwater eruption does not fall under this denomination.

These eruptions are characterized by four distinct phases. In the first volcanic materials are sea surface as bubbles of lava. Then appear a white column of steam to be followed by explosions caused by the underwater volcano and acquire darker shades. In the fourth stage would form a small island where there would be a fountain of lava that would expand until it ceased to exit.

In the current situation shallower focus of eruptive fissure eruption of El Hierro , which was located about 150 meters deep according to the information given by the PEVOLCA, seems to have closed, although the eruption may continue in deeper areas Building island of El Hierro. However, the volcanic tremor continued on CHIE seismic station that could precisely target the lava is coming out somewhere.

Possible evolution of the volcanic eruption in El Hierro

Thus, the published data on this volcanic phenomenon, although difficult to predict the possible evolution glimpse. The volcanic eruption of El Hierro could be stopped at any time, although in view of the deformation on the island is not expected to be the case in the short term.

It could also continue the rash known foci and in the case of the shallowest, and after passing through the phases of the eruption surtseyana, become an island, but for this last step came to an end would require a large input of magma from below.

If the contribution of magma is higher than the amount of lava that comes out of the different foci or if one of these will be closed for any reason, then it can happen that will open new eruptive mouths, either at sea or on land. If this happened in the sea in shallow areas may be mentioned earlier phases of the eruption surtseyana .

How could last eruption of El Hierro

In any case, the data of deformation and earthquakes in El Hierro which records the IGN, they have not stopped, at least reflect the geological process continues its course, and even may point to the arrival of more magma beneath the island. As for the duration of the volcanic phenomenon , David Calvo, non-tip, aimed at RTVE that could be extended in time but the important thing is the observation and monitoring of underwater eruption near the island to be opened from other sources if any.

Translated by Google. Written by Daniel Martin

http://www.suite101.net/news/caracteristicas-y-posible-evolucion-de-la-erupcion-en-el-hierro-a69990

Red Alert Issued In El Hierro Town As Underwater Volcano Erupts

El Hierro. Google Maps

Spain’s Instituto Geográfico Nacional (IGN) confirmed on Tuesday that an underwater eruption has occurred five kilomtres off the southern coastline of El Hierro, the smallest of the Canary Island. The eruption is Spain’s first since the eruption in 1971 of the Teneguía volcano on the island of La Palma (Canary Islands).

The IGN says all three of its seismic stations on El Hierro in the Canary Islands have registered a volcanic tremor of low frequency in the south of the island at La Restinga, the southern-most village in the Canaries.  The estimated 537 residents of the town were summonsed to a local football field on Tuesday afternoon to be briefed on evacuation procedures.

A Red Alert has since been issued by local authorities for the town. A notice posted on the Emergencia El Hierro website on Tuesday evening stated: “Phase pre-eruptive. It involves the initiation of a preventive evacuation. Make yourself available to the authorities.”

Scientists from IGN and CSIC (Consejo Superior de Investigaciones Científicas), meanwhile, have conducted a reconnaissance flight over the sea to the area south of the island, where they have located dead fish floating on the surface five kilometres from the coast. The dead fish were identified in an area where lower seismic magnitude occurred on October 9, at a depth of approximately 2 km.

The present volcanic activity is understood to be occurring at a depth of 600 metres (just under one kilometre) below sea level, in the Las Calmas sea.

Scientists from IGN, CSIC and the University of Cadiz have established their monitoring base at La Restinga. Efforts are underway to determine if the subsea volcanic vent is widening and if so, in which direction (away or toward El Hierro).

Initial reports of the eruption were received from crews on board four separate ships. Local media agency Canarias7 reported on Monday that Government authorities have suspended ferry activities to and from the 285 square-kilometre island.

English language newspaper  islandconnections.eu reported: “The martime chief for the province of Santa Cruz de Tenerife Antonio Padrón has issued a recomendation that boats should not sail closer than four miles off El Hierro. Divers have also been told to suspend all activities.”

The eruption takes place amidst an unprecedented earthquake swarm in El Hierro. The number of earthquakes recorded since July 17, 2011 on El Hierro has now exceeded 10,000.

Hierro, a shield volcano, has had a single historic eruption from the Volcan de Lomo Negro vent in 1793. The eruption lasted approximately one month and produced lava flows.

The recent surge in the number and intensity of earthquakes prompted officials from the IGN and The Canary Islands Government to raise the alert level for the Hierro volcano to ‘Yellow’ late last month. The alert remained in place on Monday, but the estimated 11,000 residents of El Hierro were being reassured not to be alarmed.

The majority of the earthquake activity shifted from El Golfo in the island’s northwest to beneath the Las Calmas Sea in the south earlier this month. Surface deformations exceeding 35mm have also been recorded on the island in recent weeks.

Evacuations

A dramatic rise in recorded earthquakes on El Hierro prompted officials to evacuate some local residents, shut El Hierro’s main tunnel, and close local schools on 27 September.

The Spanish Civil Guard (Guardia Civil) advised almost 50 residents of the municipality of La Frontera to leave their homes because of landslide fears. Two units of the Spanish military’s emergency intervention unit (EMU) were also placed on standby to depart the nearby island of Tenerife to assist in the possible evacuation of hundreds of other El Hierro residents.

Meanwhile, the island’s main tunnel (Tunel del Golfo), which links Frontera to Valverde, was shut forcing motorists to travel across the 280-sq-km island via a mountain road. The Cabildo de El Hierro also ordered the closure of schools.

Read more: http://www.irishweatheronline.com/news/earth-science/geology/red-alert-issued-in-el-hierro-town-as-underwater-volcano-erupts/41346.html