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Information on the explosive eruptie phase in Iceland

From: "Freysteinn Sigmundsson" <fs@hi.is>

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Hello,

Information on the explosive eruptie phase in Iceland

On behalf of the many contact persons.

Regards,

Freysteinn

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Freysteinn Sigmundsson

Nordic Volcanological Centre, Institute of Earth Sciences

Askja, University of Iceland

Sturlugata 7, IS-101 Reykjavik, Iceland

Phone +354 5254491 / +354 893 4607

Fax +354 562 9767

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Explosive eruptive phase of the Eyjafjallajökull volcano, Iceland, begins

14 April 2010

The eruption plume from Iceland that has caused the unprecedented

catastrophic disruption of air traffic and closure of airspaces over

northern Europe is due to an explosive eruptive phase that began at the

Eyjafjallajökull volcano on April 14. It is a continuation of eruptive

activity in the Eyjafjallajökull volcanic system that began 20 March 2010.

During an initial eruptive phase from 20 March to 12 April lava flowed

from eruptive vents on the volcano flanks, outside its ice cover. The lava

erupted in the initial phase is alkali-olivine basalt, with silica content

of about 47%.

After a short hiatus in eruptive activity a new set of craters opened up

in early morning of 14 April under the volcano’s ice covered central

summit caldera. This eruptive phase was preceded with a swarm of

earthquakes from around 23:00 on 13 April to 1:00 on 14 April. The

earthquake swarm was followed by the onset of seismic eruption tremor.

Meltwater started to emanate from the ice cap around 7 o’clock on April 14

and eruption plume was observed in the early morning. Visual observations

were limited by cloud cover over the volcano, but an airplane of the

Iceland coast Guard imaged with eruptive crates with radar instrument.

Series of vents along a 2 km long north-south oriented fissure were

active, with meltwater flowing down northern slopes of the volcano, but

also to the south. Ash loaded eruption plume rose to more than 8 km

height, deflected to the east by westerly winds.

Jokulhlaups (floods of meltwater) reached the lowlands around the volcano

with peak flow around noon on April 14, with destruction of roads,

infrastructure, and farmlands. No fatalities as people had been evacuated

from hazardous areas. Tephra fall begins in southeast Iceland. A second

jokulhlaup/lahar emanates from the ice cap down the Markarfljot valley in

the evening.

On 15 April the eruption plume reaches mainland Europe with closure of

airspace over large part of Northern Europe. Activity continues at a

similar level with ash generation and flow of meltwater in pulses.

Jokulhlaup/lahar occurs in the evening. On April 16 some variability

occurs in seismic tremor and tephra generation, but overall the eruptive

activity remains stable. Pulsating eruptive plume reaches above 8 km, with

overall height of 5 km. Large closures of airspace continue.

Chemical analyses of ash samples reveal fluorine rich intermediate

eruptive products with silica content of 58%, more evolved than in the

initial lava producing phase of the eruptive activity. The magma

composition may reflect evolution from alkali-olivine basalt by crystal

fractionation as erupted in the initial phase.