Constraining the potential respiratory health hazard from large volcanic eruptions

Part I. Inhalation of fine-grained volcanic ash particles is known to cause irritation of the airways, acute and chronic health problems. The health effects of volcanic ash inhalation depend upon particle size and the proportion of the fine ash particles. It is the respirable fraction (< 4 mum diameter) that can enter the deep parts of the lung where respiratory diseases are initiated. The amount and the proportion of respirable particles vary between volcanoes and even between eruptions of the same volcano. In order to provide a rapid form of hazard assessment, 23 ash samples from around the world were analyzed for their grain size and examined for possible correlations with the eruption dynamics parameters. The data presented here show that eruption dynamics and eruption style have a strong influence on the amount of respirable ash produced and can be used as predictive parameters in volcanic respiratory health hazard assessment.; Part II. Crystal size distribution (CSD) analysis has been applied to quartz crystals of the Ordovician Millbrig K-bentonite, which represents one of the largest fallout ash deposits known in the Phanerozoic Era, to establish crystal growth histories and conditions in the magma chamber prior to eruption. Specific CSDs were examined for crystal growth conditions. The CSDs of the Millbrig are lognormal and have concave-down shapes. Concave down CSDs are possibly an intrinsic property of phenocryst growth in large volume silicic magmas as documented in the literature. Although all samples follow concave-down shapes, two ash samples exhibit rather different CSD shapes. These findings appear to fingerprint a separate magma batch with different crystal growth conditions. Therefore, the multiple ash beds in the Millbrig must have been a product of series of separate eruptions that represent separate magma layers or batches that had different crystal growth conditions.