Tephra fall deposits of the 22-23 April 2015 Calbuco eruption: new field data and potential health hazard from ash characterization

JORGE ROMERO; ELIZABETH ROVERE; ROMINA DAGA; FABIO ARZILLI; FREDERICK SWANSON; FLORENCIA RECKZIEGEL; DANIELE MORGAVI; MARGHERITA POLACCI; JULIA JONES; CLAIRE J. HORWELL; GUSTAVO VILLAROSA

PUERTO VARAS

Congreso; Cities on Volcanoes 9; 2016

SERNAGEOMIN-IAVCEI

On22-23 April 2015 Calbuco erupted 0.26-0.28 km3 of bulk tephra (Jan 2016mapping). Scanning electron microscopy (SEM), mechanical and laser grain size,X-ray diffraction (XRD) and X-ray fluorescence (XRF) analyses were carried outon 4 proximal (5-30 km downwind; DW) and 12 distal (100-280 km DW) tephrasamples from this eruption, in order to assess its spatial variations andpotential impacts on human and animal health. Also, contours of PM5 (PM5 =<5 µm), PM10 and PM20 concentrations at ground level were computed withFALL3D. Tephra is polymodal at proximal (<6 km DW) areas, while at greaterdistances (30 and 100 km) it is unimodal, with the exception of a bimodalregion 200 km DW. The ash is basaltic andesite in composition (~55.4 wt.%SiO2), and is composed of plagioclase, volcanic glass, pyroxene (augite,diopside and orthopyroxene) and lithics. Crystalline silica was not recognizedvia XRD (e.g. quartz, cristobalite or tridimite). The ash particles arelow-vesicular, blocky glass shards, with relatively thick inter-vesicular walls,while fibrous particles were not observed within any sample. The <63 µmfraction averages 47 wt.% of bulk ash. The ?thoracic? (<10 ?m) fractionranges from 3.9 to 14.3 wt.% (13.08 ±5.23 theoretical wt.%) and consists ofirregular shards and blocky particles with inclusions of Fe Ti oxides, whichare seen to aggregate and coat larger glassy fragments (<100 ?m). The?respirable? ash (<4 µm) comprises 0.3-5.6 wt.% (5.55 ±2.22 theoreticalwt.%) in all samples. These characteristics suggest that any potential healthhazard of Calbuco ash would be related to grain size or chemical features butnot to morphology or crystalline silica content, thus silicosis is notexpected. New studies should include leachate analyses, plus clinical andepidemiological studies at areas affected by abundant fine ash recognized bydirect sampling and FALL3D modeling