Eydis Salome Eiriksdottir

Characterization of Eyjafjallajökull volcanic ash particles and a protocol for rapid risk assessment

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.

The feedback between climate and weathering

Abstract Long-term climate moderation is commonly attributed to chemical weathering; the greater the temperature and precipitation the faster the weathering rate. To test this widely-held hypothesis, we performed a field study and determined the weathering rates of eight nearly pristine north-east Iceland river catchments with varying glacial cover over 44 y. Statistically significant linear positive correlations were found between mean annual temperature and chemical weathering in all eight catchments and between mean annual temperature and mechanical weathering and runoff in seven of the eight catchments. The runoff, mechanical weathering flux, and chemical weathering fluxes in these catchments are found to increase from 6 to 16%, 8 to 30%, and 4 to 14%, respectively, depending on the catchment for each degree of temperature increase. Positive correlations were found between time and mechanical and chemical weathering for all catchments. In summary, these results demonstrate a significant feedback between climate and Earth surface weathering, and suggest that this weathering rate is currently increasing with time due to global warming.

Major impact of volcanic gases on the chemical composition of precipitation in Iceland during the 2014-15 Holuhraun eruption

The Holuhraun eruption in 2014-15 was the largest in Iceland for more than 200 years. It resulted in emissions of large quantities of volcanic gases into the atmosphere (11 Mt SO2, 0.1 Mt HCl and 0.05 Mt HF). During the eruption the volcanic gases had major effects on F, SO4 and to a lesser extent Cl concentrations in precipitation throughout Iceland, effects not observed in recent decades. The concentrations of F, Cl and SO4 (n = 705) reached values of 444 μM, 12,270 μM and 17,324 μM during the eruption and were on average ~20 times higher for F and SO4 and much lower for Cl compared to pre-eruption times. The concentrations of major cations (Si, Na, K, Ca, Mg, Al and Fe) (n = 151) in the precipitation, were taken as having originated from seawater spray and dissolution of rock dust and aerosol. Based on the mixing model developed here, it is demonstrated that the source of the enrichment of F and SO4 was indeed the volcanic gas emissions with >60-100 mol% of SO4 and F in the precipitation originated from volcanic gas, whereas the Cl originated mostly from seawater spray, making the volcanic gas input of Cl relatively less important than for F and SO4. The results showed that large volcanic eruptions can have major effects on atmospheric chemistry and impact the composition of precipitation.