Fate and agricultural consequences of leachable elements added to the environment from the 2011 Cordón Caulle Volcanic Complex tephra fall

CAROL STEWART; THOMAS WILSON; SHANE CRONIN; HEATHER CRAIG; OUTES, VALERIA; CHRISTOPHER OZE; SALLY GAW; VILLAROSA, GUSTAVO

Puerto Varas

Congreso; Cities on Volcanoes 9; 2016

SERNAGEOMIN-IAVCEI

The June 2011 eruption of Cordón Caulle Volcanic Complex,Chile, dispersed tephra over ~350,000 km2, including productive agriculturalland. This resulted in the death of nearly one million livestock. Two distinctenvironments were affected: a proximal temperate Andean setting, and thesemi-arid Argentine steppe farther from the volcano. The purpose of this studywas to better understand the fate and agricultural consequences of leachableelements added to the environment by this large silicic tephra fall. Tephra,soil and surface water samples across the depositional area were collected bothimmediately after the eruption (tephra and water) and nine months afterwards(tephra, soil and water). Tephra samples were analysed following a new hazardassessment protocol developed by the International Volcanic Health HazardNetwork (IVHHN). Water-extractable element concentrations in freshly-collectedtephra were very low to low compared to other eruptions. Surface water analysessuggested short-term changes to water composition due to the release ofelements from tephra. No effect on the fertility of soils underlying tephra wasapparent after nine months. Water-extractable fluorine (F) in freshly-collectedtephra ranged from 12-167 mg/kg, with a median value of 67 mg/kg. Based onparallels with the 11-12 October 1995 eruption of Ruapehu volcano, New Zealand,we suggest that the role of F toxicity cannot be ruled out as a contributingfactor to large-scale livestock deaths and also to reported cases of chronicfluorosis in wild deer and livestock populations in the CC-VC tephra falldepositional area. Finally, we recommend that effective response to widespreadtephra fall over agricultural areas should include: rapid, statisticallyrepresentative field sampling of tephra, soils, surface water supplies andforage crops; analysis using appropriate and reliable laboratory methods;timely dissemination of results to agricultural agencies; provision forlongitudinal sampling; and provision for reliable diagnoses of fluorosis casesthrough autopsies and chemical analysis.