Long-range volcanic ash transport and fallout during the 2008 eruption of Chaiten volcno, Chile

ADAM J. DURANT; ALFRED J. PRATA; GUSTAVO VILLAROSA; WILLIAM I. ROSE; PIERRE DELMELLE; JOSÉ G. VIRAMONTE

Viena

Congreso; European Geosciences Union General Assembly 2012; 2012

European Geosciences Union

The May 2008 eruption of Chaitén volcano, Chile, provided a rare opportunity to measure thelong-range transport of volcanic emissions and characteristics of a widely-dispersedterrestrial ash deposit. Airborne ash mass, quantified using thermal infrared satellite remotesensing, ranged between 0.2-0.4 Tg during the period 3-7 May 2008. A high level ofspatiotemporal correspondence was observed between cloud trajectories and changes insurface reflectivity, which was inferred to indicate ash deposition. The evolution of thedeposit was mapped for the first time using satellite-based observations of surfacereflectivity.The distal (>80 km) ash deposit was poorly sorted and fine grained, and mean particlesize varied very little beyond a distance >300 km. There were 3 consistent particle sizesubpopulations in fallout at distances >300 km which suggests that aggregation influencedparticle settling. Discrete temporal sampling and characterisation of fallout demonstratedcontributions from specific eruptive phases. Some evidence for winnowing was identifiedthrough comparison of samples collected at the time of deposition to bulk samples collectedmonths after deposition.X-Ray Photoelectron Spectroscopy (XPS) analyses revealed surface enrichments in Ca,Na and Fe and the presence of coatings of mixed Ca-, Na- and Fe-rich salts on ashparticles prior to deposition. XPS analyses revealed strong surface Fe enrichments (incontrast to the results from bulk leachate analyses), which indicates that surfaceanalysis techniques should be applied to investigate potential influences on oceanproductivity in response to volcanic ash fallout over oceans. Low S:Cl ratios in leachatesindicate that the eruption had a low S content, and high Cl:F ratios imply gas-ashinteraction within a Cl-rich environment. We estimate that ash fallout had potentialto scavenge 42 % of total S released into the atmosphere prior to deposition.