********************************************************************* From: Claire Horwell <claire.horwell@xxxxxxxxxxxx> ********************************************************************* A mineralogical and geochemical assessment of the potential health hazard of the Chaitén volcanic ash is now available through the International Volcanic Health Hazard Network website. Please visit www.ivhhn.org to download the full report. The key results of the report are: . Bulk composition analysis (XRF) of the samples showed that the samples are rhyolitic (72.5-74.5 wt. % SiO2). . Grain size analysis found the samples to be fine-grained, with similar grain size characteristics to the Soufrière Hills volcano (Montserrat), Mt St Helens (USA) and Merapi (Indonesia). The quantity of respirable (< 4 ?m) particles ranged from 8.8-11.9 vol %. . Morphology - the ash particles are angular, being composed of fragmented crystals and glass. It is not possible to distinguish mineralogical composition by observations of the morphology of the particles. . Crystalline silica - The cristobalite content ranges from 2.2-7.4 wt. % with the highest quantities observed in ash deposited at Jacobaci. This compares with 15-17 wt. % cristobalite from the Soufrière Hills Volcano, Montserrat, which produces abundant cristobalite in its dome. Quartz quantities range from 0.5-1.9 wt. % and no tridymite was observed. . Surface area - the surface area of the particles is low, ranging from 0.6-1.3 m2g-1 which is in keeping with analyses from other volcanoes. . Surface reactivity - all samples generated hydroxyl radicals (through an iron-catalysed reaction which can potentially be a carcinogenic and inflammatory factor in the lungs). The samples generated between 0.3-0.9 ?mol m-2 hydroxyl radicals after 30 mins. of reaction which is at the lower end of the range of results obtained previously for other volcanic ash samples. . Iron release - the Chaitén samples released low amounts of iron (a measure of the iron available for surface reactions (11.5-30.5 ?mol m-2 after 7 days incubation). These results are in keeping with the rhyolitic (high silica, low iron) magmatic composition of the samples. Health message - from Dr Peter Baxter, Cambridge University, UK The Chaitén ash is sufficiently fine to have the potential to trigger asthma attacks in susceptible people, and aggravate respiratory symptoms in people with chronic lung problems. All people should wear masks in situations where exposure to the ash is going to be high, e.g., dry, windy days and where heavy traffic or tasks such as ash removal create dust in the air. In public health terms, the potential for the development of long-term respiratory problems depends mainly upon the amount of crystalline silica in the ash and proportion of the ash which can be easily breathed into the deep parts of the lung. Taking these results into account and the experience acquired from other volcanoes over the last 25 years, the health hazard is low unless frequent eruptive activity commences which repeatedly exposes the population to high ash levels over long durations. In this case, careful monitoring of exposure and ash composition is required to make a full risk assessment. Best wishes, Claire Horwell ============================================================== To unsubscribe from the volcano list, send the message: signoff volcano to: listserv@xxxxxxx, or write to: volcano-request@xxxxxxxx To contribute to the volcano list, send your message to: volcano@xxxxxxxx Please do not send attachments. ==============================================================
