Quantifying the impact of volcanic ash on the environment
Magmatic gasses condense onto the surface of ash particles during volcanic eruptions. As the particles react with atmospheric air and water vapour, the condensed gasses form sulphuric and halogen acids and the ash surfaces dissolve. The acid leaches cations from the bulk ash and secondary minerals may precipitate as a thin coating. This coating is highly water soluble, leading to rapid dispersal of potentially harmful elements and or nutrients into the enviroment upon contact with rainfall or surface waters. Landsvirkjun Power have a number of reservoirs, on rivers in the vicinity of Mt Hekla, Iceland. If these reservoirs are loaded with volcanic ash from Hekla during future eruptions, it will potentially harm the turbines in power ploants down stream from the reservoirs, and pollute the rivers. We have sampled pristine volcanic ash samples from Icelandic explosive eruptions since 2000; Hekla 2000, Grímsvötn 2004, and 2011, and Eyjafjallajökull 2010. These samples provide a unique opportunity to study the nature of the surface coatings of the ash, down to molecular level and the isotope composition of the metal salts forming the coating.
The aim of this project is to determine the isotope composition of these surface salts and the bulk volcanic ash, and for the stable isotopes the fractionation that occurs when these salts first dissolve first in the surface environment. This will be achieved first, through controlled dissolution experiments of the ash and second, the study of river water samples taken during some of the eruptions noted above. This will involve, in particular the measurement of Li isotopes (which serve as tracers of chemical weathering processes. Fe, Si and Mg (which are additionally sensitive to bio-utilization, and the highly siderophile elements (HSEs: Os, Ir, Ru, Rh, Pt, Pd and Re). These data will allow us to develop tracers with which to quantify the impact of volcanic ash on the surface environment, and on rivers and material delivered to the oceans.