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The effusive six months long 2014-2015 Bárðarbunga eruption (31 August-27 February) was the largest in Iceland for more than 200 years, producing 1.6 ± 0.3 km 3 of lava. The total SO 2 emission was 11 ± 5 Mt, more than the amount emitted from Europe in 2011. The ground level concentration of SO 2 exceeded the 350 µg m −3 hourly average health limit over much of Iceland for days to weeks. Anomalously high SO 2 concentrations were also measured at several locations in Europe in September. The lowest pH of fresh snowmelt at the eruption site was 3.3, and 3.2 in precipitation 105 km away from the source. Elevated dissolved H 2 SO 4 , HCl, HF, and metal concentrations were measured in snow and precipitation. Environmental pressures from the eruption and impacts on populated areas were reduced by its remoteness, timing, and the weather. The anticipated primary environmental pressure is on the surface waters, soils, and vegetation of Iceland.

On April 14, 2010, when meltwaters from the Eyjafjallajökull glacier mixed with hot magma, an explosive eruption sent unusually fine-grained ash into the jet stream. It quickly dispersed over Europe. Previous airplane encounters with ash resulted in sandblasted windows and particles melted inside jet engines, causing them to fail. Therefore, air traffic was grounded for several days. Concerns also arose about health risks from fallout, because ash can transport acids as well as toxic compounds, such as fluoride, aluminum, and arsenic. Studies on ash are usually made on material collected far from the source, where it could have mixed with other atmospheric particles, or after exposure to water as rain or fog, which would alter surface composition. For this study, a unique set of dry ash samples was collected immediately after the explosive event and compared with fresh ash from a later, more typical eruption. Using nanotechniques, custom-designed for studying natural materials, we explored the physical and chemical nature of the ash to determine if fears about health and safety were justified and we developed a protocol that will serve for assessing risks during a future event. On single particles, we identified the composition of nanometer scale salt coatings and measured the mass of adsorbed salts with picogram resolution. The particles of explosive ash that reached Europe in the jet stream were especially sharp and abrasive over their entire size range, from submillimeter to tens of nanometers. Edges remained sharp even after a couple of weeks of abrasion in stirred water suspensions.

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Citation for published item:ogge von trndmnnD FeFiF nd furtonD uFF nd ypfergeltD F nd iir¡ %ksd¡ ottirD iFF nd wurphyD wFtF nd iinrssonD eF nd qislsonD FF @PHITA 9he e'et of hydrotherml spring wethering proesses nd primry produtivity on lithium isotopes X vke wyvtnD selndF9D ghemil geologyFD RRS F ppF REIQF Further information on publisher's website: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. for Lake Myvatn, Iceland. We also present a time-series from the Laxa River, 25 which is the single outflow from the lake. The  7 Li values in the input springs to 26 Lake Myvatn are highly variable (5-27‰), and correlate inversely with 27 temperature and total dissolved solids. These co-variations imply that even in 28 such waters, the processes controlling  7 Li variations during weathering still 29 operate: that is, the ratio of primary rock dissolution to secondary mineral 30 formation, where the latter preferentially incorporates 6 Li with a temperature-31 dependent fractionation factor. In high-temperature geothermal waters 32 (>300°C) secondary mineral formation is inhibited, and has a low fractionation 33 2 factor, leading to little  7 Li fractionation. Even in waters that have cooled 34 considerably over several months from their geothermal temperatures, 35 fractionation is still low, and  7 Li values are similar to those reported from 36 waters measured at >350°C. In contrast, cooler groundwaters promote relatively 37 high proportions of clay formation, which scavenge dissolved solids (including 38 6 Li). The time series on the Laxa River, the single outflow from Lake Myvatn, 39 shows little  7 Li variation with time over the 12 month sampling period (17-40 21‰), demonstrating that in contrast to tracers such as Si isotopes, Li isotopes 41 are unaffected by the significant seasonal phytoplankton blooms that occur in 42 the lake. Thus, these results clearly illustrate that Li isotopes are ideally suited to 43 constrain silicate weathering processes, because fractionation by secondary 44 mineral formation operates even when groundwater and hydrothermal inputs 45 are significant, and because Li isotopes are demonstrably unaffected by 46 phytoplankton or plant growth. 47

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