| Summary: | The April-May 2010 eruption of Eyjafjallajökull volcano (Iceland) was characterized by a nearly continuous injection of tephra in the atmosphere that affected various economic sectors in Iceland and caused a global-wide interruption of air traffic. Eruptive activity during 4-8 May 2010 was characterized based on short-duration physical parameters in order to capture transient eruptive behavior of a long-lasting eruption (i.e., total grainsize distribution, erupted mass and mass eruption rate averaged over 30-minute activity). Resulting 30-minute total grainsize distribution based on both ground and MSG-SEVIRI satellite measurements is characterized by Mdphi of about 2 phi and a fine-ash content of about 30wt%. Accumulation rate varied by two orders of magnitude with an exponential decay away from the vent, whereas Mdphi shows a linear increase until about 18 km from vent reaching a plateau of about 4.5 phi between 20-56 km. Associated mass eruption rate is in between 0.6-1.2 x 10^5 kg s^-1. In-situ sampling showed how fine ash mainly fell as aggregates of various typologies. About 5 to 9 wt% of the erupted mass remained in the cloud up to 1000 km from the vent, suggesting that nearly half of the ash >7 phi settled as aggregates within the first 60 km. Particle sphericity and shape factor varied between 0.4 and 1 with no clear correlation with size and distance from vent. Our experiments also demonstrate how satellite retrievals and Doppler radar grainsize detection can provide real-time description of the source term but for a limited particle-size range.
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