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Sediment cores from lakes and bogs in the Río Cisnes valley contain tephra from explosive eruptions of volcanoes in the southern part of the Andean Southern Volcanic Zone (SSVZ). These tephra, which thicken and coarsen to the west, are attributed to eruptions from Melimoyu, Mentolat, Hudson, and potentially either Macá, Cay or one of the many minor eruptive centers (MEC) located both along the Liquiñe-Ofqui Fault Zone (LOFZ) and surrounding the major volcanoes. Correlation of the tephra between two new cores in the lower Río Cisnes valley, and amongst other cores previously described from the region, and source volcano identification for the tephra, has been done using lithostratigraphic data (tephra layer thickness and grain size), petrography (tephra glass color, vesicle morphology, and type and abundance of phenocryst phases), and by comparison of bulk tephra trace-element characteristics with previously published whole-rock and bulk tephra chemical analysis. Four tephras in these cores are attributed to eruptions of Mentolat, four to eruptions from Melimoyu, one possibly to Hudson, and six cannot be assigned to a specific source volcano. Some of these tephra correspond to pyroclastic tephra fall deposits previously observed in outcrop, including the MEL2 eruption of Melimoyu and the MEN1 eruption of Mentolat. However, others have not been previously observed and represent the products of newly identified small to medium sized eruptions from volcanoes of the SSVZ. These results provide new information concerning the frequency and magnitude of explosive eruption of SSVZ volcanoes and contribute to the evaluation of volcanic hazards in the region. RESUMEN Los testigos de sedimentos de lagos y pantanos obtenidos en el valle del río Cisnes contienen niveles de tefra originados por erupciones explosivas de volcanes localizados en la parte sur de la Zona Volcánica de los Andes del Sur (SZVS). Estos depósitos de tefra, que aumentan de espesor y tamaño del grano hacia el oeste, son atribuidos a erupciones de los volcanes Melimoyu, Mentolat, Hudson y potencialmente a los volcanes Macá, Cay o alguno de los numerosos centros eruptivos menores (CEM) localizados a lo largo de la Zona de Falla Liquiñe-Ofqui (ZFLO) y que rodean a los volcanes principales. La correlación de los niveles de tefra identificados en dos nuevos testigos, obtenidos en el curso inferior del valle del río Cisnes, con aquellos presentes en testigos descritos con anterioridad en la región y la identificación de los volcanes fuente de las tefras, se realizó con la ayuda de datos litoestratigráficos, (espesor de la capa de tefra y tamaño del grano), petrografía (color de los fragmentos de vidrio, morfología de las vesículas y tipo y abundancia de fenocristales) y por comparación de sus patrones de elementos trazas con análisis químicos de roca total y tefra total publicados con anterioridad. Cuatro niveles de tefras identificados en estos nuevos testigos se atribuyen a erupciones del volcán Mentolat, otros cuatro se asignan al volcán Melimoyu y uno, posiblemente, fue originado por el volcán Hudson. Otros seis no pueden ser asignados a un volcán específico. Algunas de estas tefras corresponden a depósitos de tefras observados previamente en afloramientos, asignados a las erupciones MEL 2 del volcán Melimoyu y MEN 1 del volcán Mentolat. Sin embargo, otros niveles de tefra no han sido reconocidos previamente y representan los productos de erupciones de tamaño pequeño a mediano de los volcanes de la SZVS recientemente identificadas en este trabajo. Estos resultados proporcionan nueva información sobre la frecuencia y magnitud de las erupciones explosivas de los volcanes de la SZVS y contribuyen a la evaluación de los peligros volcánicos en la región.

Sediment cores from lakes and bogs in the Río Cisnes valley contain tephra from explosive eruptions of volcanoes in the southern part of the Andean Southern Volcanic Zone (SSVZ). These tephra, which thicken and coarsen to the west, are attributed to eruptions from Melimoyu, Mentolat, Hudson, and potentially either Macá, Cay or one of the many minor eruptive centers (MEC) located both along the Liquiñe-Ofqui Fault Zone (LOFZ) and surrounding the major volcanoes. Correlation of the tephra between two new cores in the lower Río Cisnes valley, and amongst other cores previously described from the region, and source volcano identification for the tephra, has been done using lithostratigraphic data (tephra layer thickness and grain size), petrography (tephra glass color, vesicle morphology, and type and abundance of phenocryst phases), and by comparison of bulk tephra trace-element characteristics with previously published whole-rock and bulk tephra chemical analysis. Four tephras in these cores are attributed to eruptions of Mentolat, four to eruptions from Melimoyu, one possibly to Hudson, and six cannot be assigned to a specific source volcano. Some of these tephra correspond to pyroclastic tephra fall deposits previously observed in outcrop, including the MEL2 eruption of Melimoyu and the MEN1 eruption of Mentolat. However, others have not been previously observed and represent the products of newly identified small to medium sized eruptions from volcanoes of the SSVZ. These results provide new information concerning the frequency and magnitude of explosive eruption of SSVZ volcanoes and contribute to the evaluation of volcanic hazards in the region.

Two Holocene tephras encountered in outcrops, cores and trenches in bogs, and lake cores in the area around Cochrane, southern Chile, are identified (based on their age, tephra glass color and morphology, mineralogy, and both bulk and glass chemistry) as H1 derived from Hudson volcano, and MEN1 derived from Mentolat volcano. New AMS radiocarbon ages indicate systematic differences between those determined in lake cores (MEN1=7,689 and H1=8,440 cal yrs BP) and surface deposits (MEN1=7,471 and H1=7,891 cal yrs BP), with the lake cores being somewhat older. H1 tephra layers range from 8 to 18 cm thick, suggesting that both the area of the 10 cm isopach and the volume of this eruption were larger than previously suggested, but not greatly, and that the direction of maximum dispersion was more to the south. MEN1 tephra layers range from 1-4 cm in thickness, indicating that this was probably a reasonably large (>5 km³) eruption. Some of the lake cores also contain thin layers (5km³). Algunos testigos lacustres también incluyen niveles más finos (