Sunday, April 18, 2010

Icelandic eruption - eyjafjallojokull volcano

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.

Eyafallajökull: subglacial volcanic eruption (continued)

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.

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