Why did the Eyjafjallajokull erupt?

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Eyjafjallajökull - Subglacial volcanism in Iceland

Whether the Eyjafjallajökull is a stratovolcano or a shield volcano is a matter of controversy among experts. It is certain that the subglacial volcano has a caldera at its summit, which is covered by a 150-200 m thick ice sheet. The caldera has a diameter of 3 x 4 kilometers and contains several craters.

The formation of the volcano began around 800,000 years ago. 12 eruption cycles of Eyjafjallajökull are known from the times before the conquest of Iceland and only 4 eruptions since there have been people on the island. These took place in the years 920, 1612-1613 and 1821-1823. The last eruption so far occurred in spring 2010. The three previous eruptions were followed by the neighboring volcano Katla a short time later.

Eyjafjallajökull lies on a NE-SW trending fissure system that forms the eastern volcanic zone of Iceland. The divergence of this fault zone is due to the fact that the European continental plate is moving away from the North American plate here. This creates a spreading zone along which magma can rise from the earth's mantle. The eastern volcanic zone stretches from the Westman Islands, over the Eyjafjallajökull-Katla system and further over the Laki Fissure, to below the Vatnajökull glacier. A few more subglacial volcanoes such as Barabunga and Grimsvötn formed there.

Pictures from Eyjafjallajökull

Long shot of the eruption crevice at Fimmvörduhals Pass.

Eruption crevice at the Fimmvörduhals Pass.

Eruption cloud and the Eyjafjallajökull.


The volcanic rock of Eyjafjallajökull consists mainly of a transition basalt between tholeiite and alkali basalt. Andesite, Dazite and Trachyte were also promoted. These rocks suggest that basaltic magma differentiates over long periods of time in the magma chamber.
The eruption on the volcano is as different as the rocks; purely effusive eruptions are known, as are explosive eruptions and volcanic eruptions, which combined both types of eruptions. Explosive eruptions are predominantly of the volcanic eruption type; But volcanologists also discovered evidence of a large Plinian eruption in prehistoric times. The 1612 eruption began with a magmatophreatic eruption and ended with Strombolian activity.

The last eruption in spring 2010 took place in two phases. First, an effusive fissure opened on the western flank of the volcano. The crevice was created on a saddle between Eyjafjallajökull and Myrdalsjökull and interrupted the hiking trail at the Fimmvörduhals pass at an altitude of 1000 m. The hiking trail connected the Skogar waterfall on the south coast with the Thormörk valley in the north of the glacier. During this eruption phase, red-hot lava fountains and lava flows were produced. Shortly after the end of the first eruption phase, the second phase followed: an explosive eruption of the volcanic type that started from the summit caldera of Eyjafjallajökull. Melt water increased the explosiveness of the eruption and a powerful ash cloud rose up to 9 km high. It was directed south by strong air currents. On the second day of the volcanic eruption, the airspace had to be closed over large parts of Europe, including in Germany.

The ice cover makes exploring the volcano difficult. Before the volcanic eruption in 2010, relatively little was known about Eyjafjallajökull. It was only in the course of the eruption that interest arose and the most modern measuring methods were used. Radar images of the ice-covered caldera were taken from an airplane. Some of the data such as seismics and LiveCam are available to the public via the Internet.

A glacier tongue (Gígjökull) extends from the summit caldera and extends down to an altitude of 1200 m. Meltwater runs above it into the Markarfljót River. This flows into the Sandere Plain on Iceland's south coast near Thorsmörk.
Volcanic eruptions under the ice of the glaciers harbor a particular danger: a glacier run (Jokulhlaup) can arise from meltwater that is formed by the heat of the eruption and accumulates under the glacier. It usually takes days or weeks for the meltwater to break through at the foot of the glacier and flood the sander plains in a tremendous flood.

Eyjafjallajökull means translated into German something like "island glacier". This name goes back to the fact that the volcano looks like an island under the ice from the Westman Islands, which are 50 km away.
The name Eyjafjallajökull actually refers to the glacier, whereby "Jokull"in Icelandic"glacier"means. The volcano should therefore"Eyjafjalla"(ie" island "), which in turn could cause confusion. The name also appears in English-language literature"Eyjafjoll", or"Eyjafjöll"During 2010 coverage, the tongue twister's pronunciation posed a problem for many reporters; Icelanders pronounce the name" Eyja, fjatla, jökytl ".

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