Phase 1: Effusive eruption 2010 eruptions of Eyjafjallajökull

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1 phase 1: effusive eruption

1.1 evacuations
1.2 effects on river
1.3 fissure





phase 1: effusive eruption

the first phase of eruption lasted 20 march 12 april 2010 , characterised olivine basaltic andesite lava flowing various eruptive vents on flanks of mountain.


evacuations

about 500 farmers , families areas of fljótshlíð, eyjafjöll, , landeyjar evacuated overnight (including group of 30 schoolchildren , 3 teachers caistor grammar school in england), , flights , reykjavík , keflavík international airport postponed, on evening of 21 march, domestic , international air traffic allowed again. inhabitants of risk zone of fljótshlíð, eyjafjöll, , landeyjar area allowed return farms , homes after evening meeting civil protection department on 22 march , evacuation plan temporarily dismissed. instead, police closed road Þórsmörk , four-wheel-drive trail skógar village fimmvörðuháls mountain pass, these roads , trails reopened on 29 march, though suitable four-wheel drives. when second fissure appeared, road closed again because of danger of flash floods, have developed if fissure had opened near big ice caps or other snow reservoirs, road again opened @ around noon on 1 april.


effects on river

on 22 march, flow meter device in krossá glacial river (which drains eyjafjallajökull , mýrdalsjökull glaciers) in Þórsmörk area (a few kilometres north-west of erupting location) started record sudden rise in water level , in water temperature – total water temperature rose 6 °c (11 °f) on two-hour period, had never happened in krossá river since measurements began. shortly afterward, water level returned normal , water temperature decreased. rise in water temperature thought related eruption nearby , affecting part of krossá drainage basin. temperature of hruná river, flows through narrow hrunárgil canyon, part of lava stream flowing, recorded geologists between 50 , 60 °c (122 , 140 °f), indicating river cooling lava in canyon.


fissure

second fissure, viewed north, on 2 april 2010


the first phase of 2010 eruption began late on evening of 20 march @ eyjafjallajökull.


the initial visual report of eruption @ 23:52 gmt, when red cloud seen @ north slopes of fimmvörðuháls mountain pass, lighting sky above eruptive site. eruption preceded intense seismicity , high rates of deformation in weeks before eruption, in association magma recharging of volcano. before eruption, depth of seismicity had become shallow, not enhanced had been in previous weeks. deformation occurring @ rates centimetre day since 4 march @ various gps sites installed within 12 km (7.5 mi) eruptive site.


a fissure opened 150 metres (490 ft) in length running in north-east south-west direction, 10 12 erupting lava craters ejecting lava @ temperature around 1,000 °c (1,800 °f) 150 m (490 ft) air. lava alkali olivine basalt , relatively viscous, causing motion of lava stream west , east of fissure slow. molten lava flowed more 4,000 m (13,000 ft) north-east of fissure , hrunagil canyon, forming lava fall more 200 m (660 ft) long , approaching Þórsmörk, had not yet reached flood plains of krossá.


on 25 march 2010, while studying eruption, scientists witnessed, first time in history, formation of pseudocrater during steam explosion. crustal expansion continued @ Þorvaldseyri 2 days after eruption began, decreasing whilst volcanic activity increasing. indicates rate @ magma flowing magma chamber equaled rate @ being lost due eruption, giving evidence phase of volcanic activity reached equilibrium.


a new fissure opened on 31 march, around 200 m (660 ft) north-west of original fissure. many witnesses present while new fissure opened. bit smaller, around 300 m (980 ft) long according witnesses, , lava coming started flow hvannárgil canyon. these 2 erupting fissures shared same magma chamber, according geophysicists. no unusual seismic activity detected @ time new fissure appeared, nor crustal expansion according many seismometers , gps recorders situated in nearby areas.


geophysicist magnús tumi einarsson said (at press meeting in hvolsvöllur on 21 march) eruption small compared to, example, eruption of hekla in 2000. eruption, rather taking place under ice cap of glacier, occurred in mountain pass between eyjafjallajökull , mýrdalsjökull glaciers. long fissure not near glacier, risk of flooding minimal; however, fissure extend ice cap, thereby increasing risk of flooding.








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