CONICET | Buscador de Institutos y Recursos Humanos

The June 2011 eruption ofCordón Caulle volcano, Chile, dispersed tephra over ~ 350,000 km2,including productive agricultural land. This resulted in the death of nearlyone million livestock. Two distinct environments were affected: a proximaltemperate Andean setting, and the semi-arid Argentine steppe farther from thevolcano. The purpose of this study was to better understand the fate andagricultural consequences of leachable elements added to the environment bythis large silicic tephra fall. Tephra, soil and surface water samples acrossthe depositional area were collected both immediately after the eruption(tephra and water) and nine months afterwards (tephra, soil and water). Tephrasamples were analysed following a new hazard assessment protocol developed bythe International Volcanic Health Hazard Network (IVHHN). Water-extractableelement concentrations in freshly-collected tephra were very low to lowcompared to other eruptions, and showed no trends with distance from thevolcano. Surface water analyses suggested short-term changes to watercomposition due to the release of elements from tephra. No effect on thefertility of soils underlying tephra was apparent after nine months.Water-extractable fluorine (F) in freshly-collected tephra ranged from 12 to167 mg/kg, with a median value of 67 mg/kg. Based on parallels withthe 11?12 October 1995 eruption of Ruapehu volcano, New Zealand, we concludethat F toxicity was a possible contributing factor to the large-scale livestockdeaths as well as to chronic fluorosis widely reported in wild deer populationsacross the Cordón Caulle tephra depositional area. Finally, we recommend thateffective response to widespread tephra fall over agricultural areas shouldinclude: (1) rapid, statistically representative field sampling of tephra,soils, surface water supplies and forage crops; (2) analysis using appropriateand reliable laboratory methods; (3) modelling both short and long-term impactson the ecosystem, especially for elements that may generate chronic hazard; (4)timely dissemination of results to agricultural agencies; (5) longitudinalsampling and monitoring to adapt impact models; and (6) developing reliableanimal fatality diagnoses through autopsies and chemical analysis.