Volcanic ash-leachates: a review and recommendations for sampling methods

Tephra in plumes can scavenge and thereby rapidly deposit volatiles including sulphur, halogen and metal species. These may then be leached (e.g. by rainfall), potentially releasing heavy loadings to soils and water bodies. Several eruptions have resulted in contamination of pasture, sometimes with serious impacts on livestock. Water quality has also been an issue in some areas affected by tephra fall. This work synthesises the literature on volcanic ash-leachates and considers the controls on volatile adsorption. General trends emerge for basaltic, intermediate and silicic tephra, as well as for variable particle size and transport distance. The applications of ash-leachate data to plume-gas geochemistry, calculation of volatile budgets and environmental impact assessment are evaluated. Comparisons for different eruptions are hampered by disparities in leachate analysis techniques. A standardised methodology is therefore proposed to facilitate future health impact assessment and volcanological interpretation of results from different sites.