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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.

Based on their petrography and chemistry, 18 tephra analyzed from two lake and bog cores and one outcrop in the upper Río Cisnes valley are believed to have been derived from nine different eruptions of the Mentolat volcano, four of the Melimoyu volcano, and one from the Hudson volcano. Some of these tephra correlate chronologically and petrochemically with previously documented large eruptions of these volcanoes, including the Late-Glacial Ho eruption of Hudson (17,340 cal yrs BP), the mid-Holocene MEN1 eruption of Mentolat (7,710 cal yrs BP), and the Late-Holocene MEL2 eruption of Melimoyu (1,680 cal yrs BP). A Melimoyu-derived tephra from the outcrop occurs in glacial-lacustrine sediments and is considered to pre-date the Last Glacial Maximum (>19,670 cal yrs BP). The data suggest that none of the tephra were produced by explosive eruptions of the Maca, Cay and Yanteles volcanoes.

Based on their petrography and chemistry, 18 tephra analyzed from two lake and bog cores and one outcrop in the upper Río Cisnes valley are believed to have been derived from nine different eruptions of the Mentolat volcano, four of the Melimoyu volcano, and one from the Hudson volcano. Some of these tephra correlate chronologically and petrochemically with previously documented large eruptions of these volcanoes, including the Late-Glacial Ho eruption of Hudson (17,340 cal yrs BP), the mid-Holocene MEN1 eruption of Mentolat (7,710 cal yrs BP), and the Late-Holocene MEL2 eruption of Melimoyu (1,680 cal yrs BP). A Melimoyu-derived tephra from the outcrop occurs in glacial-lacustrine sediments and is considered to pre-date the Last Glacial Maximum (>19,670 cal yrs BP). The data suggest that none of the tephra were produced by explosive eruptions of the Maca, Cay and Yanteles volcanoes. Dieciocho tefras provenientes de testigos de un lago y un mallín, junto a un perfil expuesto en el alto valle del río Cisnes fueron caracterizadas sobre la base de su petrografía y química y corresponderían a nueve diferentes erupciones del volcán Mentolat, cuatro del volcán Melimoyu y una del volcán Hudson. Algunas de estas tefras se correlacionan cronológica y petroquímicamente con grandes erupciones de estos volcanes previamente documentadas, incluyendo la erupción Ho del volcán Hudson (Tardiglacial, 17.340 años cal. AP), la erupción MEN1 del volcán Mentolat (Holoceno medio, 7.710 años cal. AP) y la erupción MEL2 del volcán Melimoyu (Holoceno tardío, 1.680 años cal. AP). Una tefra perteneciente a la erupción del volcán Melimoyu, hallada en un perfil expuesto en un contexto de depósitos glaciolacustres, tiene una edad (>19.670 años cal. AP) que precede al término del Último Máximo Glacial en Patagonia Central. Los datos sugieren que ninguna de las tefras fueron producidas por erupciones explosivas de los volcanes Maca, Cay y Yanteles.