The Eyjafjallajokull 2010 eruption was an extraordinary event in that it led to widespread over Europe. Volcanicprocesses which lead to eruptions can be investigated by monitoring a variety of parameters, including the compositionof ash leachates. Fine-grained tephra erupted from active vents, and transported through volcanic plumes,can adsorbs, and therefore rapidly scavenge, volatile elements such as S, halogens, and metal species in the formof soluble salts adhering to ash surfaces. Analysis of such water-soluble phases is a suitable complement for the remotesensing of volcanic gases at inaccessible volcanoes, like Eyjafjallajokull. The 2010 Eyjafjallajokull eruptiondeveloped in four main phases, whose difference in gas chemistry and products has been marked in ash-leachatesdata too. The recurrent ash fallout provided a unique opportunity to characterize the compositional features ofash leachates, and to identify their relation (if any) with the eruptive activity styles of the volcano. By these considerations,we report on the chemical composition of leachates of 20 volcanic ash samples deposited during themost explosive Eyjafjallajokull activities (from 14 April to 8 May) and during the lava fountaining event (on 26thMarch 2010). We found that ash-leachate solutions are dominated - among cations - by Na and Ca, while theydisplay nearly equal S : Cl : F abundances (mean S=Cl and S=F molar ratios of 0.85 and 0.33, respectively),as characteristic of divergent-plate and within-plate volcanism. The strong correlations between leached Ca F,Ca SO4, and Na Cl (r2 = 0:7 0:9), suggest that fluorite, anhydrite, and halite are the most likely solublesurface minerals formed in the plume (and therefore leached during our experiments), as also reported at manyactive volcanoes. Our data bring evidence for variations in S and halogens proportions, with samples from 5 8thMay which show the highest S=Cl and lowest Cl=F ratios. By combining the concentration of leached SO4, Fand Cl with the mass/area ratio of deposited ash (normalized to 30 min of 5-8 May 2010 volcanic phase), weestimated mean depositional elemental fluxes of about 1:0 10 5, 1:1 10 3 and 1:2 10 3 g m 2s 1, for thewater-soluble SO4, Cl and F, respectively. By integrating these data over the whole sampling area, we estimateda total depositional flux of about 864, 605 and 691 t day 1, for SO4, Cl and F, respectively. These data meanthat 15% of Sgas and 29% of Clgas discharged into the plume during the same eruptive phase, may have beenscavenged by adsorption processes on ash surfaces within the eruption column.
|Numero di pagine||1|
|Stato di pubblicazione||Published - 2012|