| Summary: | On 14 April 2010 the summit of Eyjafjallajökull started to erupt, following an effusive eruption at the volcanoes flank. This was a hybrid eruption that featured pulsating explosive activity along with lava effusion. On 17 April 2010, which is the focus of this study, the magma discharge rate was estimated around 6.0 x 105 kg s-1 with a plume reaching over 9 km. Plume monitoring covering seven hours of the afternoon on the 17th, revealed eight distinct pulsating periods of dark explosive plume pulses, following periods of little or no activity. The deposits from the afternoon on 17 April consists of six alternating pumice lapilli and ash-grade units, thus matching the main pulses of explosive activity. The sampled tephra units contain fairly high amounts (7-45%) of ash (<2 mm), which presence at such a proximal site is best explained by ash aggregation induced by water vapor derived from the melted glacier ice. Density measurements, along with image analysis of the vesicles, revealed mainly two types of clasts: 1) Pumices, typified by densities of 600 to 1000 kg m-3) and showing evidence of at least two nucleation events and substantial growth upon decompression. 2) Juvenile lithics with densities of 1400 to 1800 kg m-3, outgassed and with evidence of collapsed bubble framework. A formation of a plug from outgassed magma at top of the rising magma column is proposed as the mechanism controlling the pulsating explosive activity on 17 April 2010. Þann 14 apríl 2010 hófst blandgos í toppgíg Eyjafjallajökuls sem myndaði hvort tveggja benmorít gjósku og hraun. Þann 17. apríl 2010, sem er dagurinn sem er til umfjöllunar í þessari ritgerð var sprengigosið í hámarki. Kvikuframleiðni gossins var um 6.0x105 kg s-1 og gosstrókurinn náði í meira en 9 km hæð. Athuganir á gosmekkinum á sjö klukkustunda tímabili þann 17. apríl sýna átta afgerandi tímabil þar sem gosmökkurinn var kraftmikill og dökkur á litinn (þ.e. öskuríkur). Þessi tímabil voru aðskilin af tímabilum þar sem sprengivirknin lá niðri og gosmökkurinn var ...
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