Flavia María Salani

Environmental assessment of 1991 Hudson volcano eruption ashfall effects on southern Patagonia region, Argentina

The August 1991 eruption of the Hudson volcano in the southern Andean volcanic zone affected an area of 1000 km in radius to the east in the Argentine Patagonic meseta. The thickness of ash ranged from 20 cm in the Andean area to less than 1 mm in the Atlantic coast zone. Wind storms reactivated the ash deposits, together with terrigenous material, more than one year after the eruption. In order to assess the potential risk of the ash, analyses of concentration, size, mineralogical composition, toxic elements, and irritating effects of gases were performed. In all samples, the percentage of particles of the 2-to 5-μm range is below the toxic threshold level. Trace elements are below the toxic threshold concentration for humans and animals. The major impact of the ashfall was on sheep herds; about one third of them were lost in the areas close to the volcano. Soil incorporated the ash layers, and a fast recovery of orchards was reported two years later. Rivers were loaded with sediment in the immediate aftermath, but one year later returned to previous conditions. Along the shores of the Buenos Aires Lake, a fresh tephra layer can be distinguished.

Petrografia, origen y paleoambiente sedimentario de las piroclastitas de la Formacion Remoredo (Jurasico Temprano), Argentina (35º30'S-70º15'W) .

Mediante el analisis de las facies piroclasticas de la Formacion Remoredo que afloran alrededor de un intrusivo fenoandesitico (Andesita Cerro Negro) se reconocieron dos asociaciones de facies: la Asociacion de Tobas Brechosas y la Asociacion de Tobas. Estas se interpretaron, respectivamente, como brechas coignimbriticas proximales e ignimbritas asociadas con depositos de caidas coignimbriticas, todas derivadas de colapsos gravitacionales de columnas eruptivas. Las paleo-corrientes, estructuras internas y proveniencia de los liticos senalan a la Andesita Cerro Negro como una de las bocas de emision, sin descartar otras localizadas al oeste del area de estudio. Las tobas de la seccion media de la Formacion Remoredo se depositaron en un lago efimero mientras las restantes lo hicieron bajo condiciones subaereas.