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Mondaca Volcano lahar of December 3, 1762, Maule Region (35°28’S): one of the largest volcanic disasters in Chilean history
No full textThe Mondaca Volcano comprises a thick rhyolitic lava-field and a dome of similar composition, located near the Lontué River Valley headwaters in the northern part of the Southern Andes Volcanic Zone. It reaches a total volume of ~0.85 km3, and it is formed by 4 subunits, named Mondaca 1, 2, 3 and 4, which correspond to successive rhyolitic blocky lava flows, emitted from a rounded dome structure. They present well-preserved flow structures and, in the surroundings, restricted to the south and east of the dome, pyroclastic fall, as well as block and ash deposits are also exhibited. Downstream, along the Lontué River, a laharic deposit is recognized. The lahar was produced after the collapse of an ephemeral ~0.44 km3 lake generated after the river obstruction by viscous lavas, during the 1762 first eruptive phase. Proximal lahar facies are well exposed between 5 and 30 km from their source. The profuse agricultural activity has completely obliterated the lahar’s medium facies deposits along the Central Depression, but are well identified at the mouth of the Mataquito River, 180 km downstream, as a beige-coloured layer, interbedded within dark coastal beachsands. The identification of overflows and super-elevation deposits formed during the debris flow emplacement along the Lontué River valley, allows to determine a high flow mobility, with estimated velocities that locally reached up to 114 km/h. Petrographic characteristics in addition to chemical composition of lavas from the volcano, pyroclasts and juvenile blocks of the laharic deposit, indicate that all they correspond to high K calcoalkaline rhyolites with subalkaline affinity. These backgrounds, together with the geographical continuity between the lavas and debris deposits along the Lontué and Mataquito rivers, verify facies correlation and common origin as the result of the 1762 Mondaca Volcano eruption complex evolution. Although it was a mainly effusive eruption that could not be observed from Curicó, the collateral consequences would have been catastrophic over a vast area to the south of that city, and evidences one of the largest volcanic disasters in Chilean history. Probably because of the low density polulation at that time, the consequences could have been minor.pp.514-52
Evaluación de peligro por remoción en masa en los sectores: Tres Espinos, Población Miramar y Agua de la Piedra, comuna de Valdivia, región de Los Ríos
No full textRevisor: Paola Ramírez ; Código de identificación interno: INF-LOS RIOS-07.202115 p
Caracterización y reconstrucción del deslizamiento Agassiz mediante el uso de datos geoespaciales. Patagonia Austral, Argentina
No full textLa glaciación y deglaciación modifican las tensiones de las laderas afectadas por estos procesos y pueden desencadenar su inestabilidad y deslizamientos. En el presente estudio se describe, caracteriza y reconstruye un deslizamiento rotacional de suelo y material morrénico de gran magnitud, ocurrido el 10 de febrero de 2013, sobre la ladera oeste del canal Upsala, brazo norte del lago Argentino, en la Patagonia Austral. Con este fin, se realizó un análisis cualitativo del estado de la ladera en épocas anteriores y posteriores a la fecha de ocurrencia del deslizamiento, se analizaron los posibles factores condicionantes y desencadenantes de la remoción en masa, y las consecuencias destructivas del tsunami relacionado que afectó las márgenes del lago. Para la reconstrucción del estado de las laderas antes y después del evento, se utilizaron técnicas de fotointerpretación de imágenes satelitales ópticas, modelos digitales de elevación, fotografías históricas, observaciones in situ, datos batimétricos y relatos del personal de guardaparques del Parque Nacional Los Glaciares. El retroceso del glaciar Upsala ha ocasionado la relajación de las laderas del canal condicionando así su estabilidad. Entre los factores condicionantes y desencadenantes que alimentaron el proceso de activación y generación del evento de remoción en masa se destacan la presencia de material morrénico no consolidado que cubre las laderas del canal, las pendientes empinadas expuestas hacia el Este, lo que aumenta su exposición al sol y derretimiento de nieve acumulada durante el invierno, y la existencia de procesos de reptación de suelo. Aunque se desconoce el factor gatillante específico se puede mencionar la saturación de los sedimentos por escurrimiento superficial e infiltraciones de agua, eventualmente lluvias intensas, erosión del pie de la ladera por la actividad glacial y la actividad sísmica local y regional como potenciales factores desencadenantes. La ladera mostró indicios de inestabilidad por más de 20 años antes de la generación del deslizamiento, y en la actualidad existen evidencias de que puede sufrir nuevas remociones en masa.pp.557-57
Reporte de visita técnica: Sector cerro La Virgen y cerro Corcovado, comuna de Coronel, región del Biobío
No full textRevisor: Alejandro Alfaro y Carolina Jara7 p
Remociones en masa e inspección de actividad de laderas en ruta W-637, comuna de Puqueldón, Provincia de Chiloé, región de Los Lagos
Get PDFInforme Técnico INF-Los Lagos-04.2021 -- Unidad Ejecutora: Oficina Técnica Puerto Varas, Región de Los Lagos17 p
Evaluación geológica del talud de la cuesta Beauchef en el ingreso sur a Río Bueno, comuna de Rio Bueno, región de Los Ríos
Get PDFRevisor: Paola Ramírez ; Código de identificación interno: INF-LOS RÍOS-11.202113 p
Antecedentes sobre el estado de los recursos hídricos del sector Cuarta Terraza-Alerce, Puerto Montt, Región de Los Lagos
No full textInforme Técnico INF-Los Lagos-05.2021 -- Unidad Ejecutora: Oficina Técnica Puerto Varas, Región de Los Lagos25 p
Evaluación de susceptibilidad de remociones en masa en calles Circunvalación Escuela Agrícola con Valle Colonia, comuna de Coyhaique, región de Aysén del General Carlos Ibáñez del Campo
No full textRevisor: Paul Duhart16 p
Quaternary glaciolacustrine deposits around a Triple Junction site: Paleolakes at the foot of the Northern Patagonian Ice field (Argentina and Chile)
No full textThe area involved by the triple junction between the South American, Nazca and Antarctic plates activity was affected by Quaternary glaciations. Before 12,800 yrs BP an extended ice field occupied the top of the Patagonian Andes, irradiating glaciers towards the east and the west dominantly. Towards the east, the ice melted in piedmont lakes; towards the west, fjords melted into the Pacific Ocean. The Upper-Pleistocene climate amelioration caused the recession of those glaciers. Some piedmont lakes reversed their Atlantic outflow towards to the Pacific Ocean. The glaciers retreat caused the fluvial reactivations along crustal former faults that were located below the ice. The Patagonian ice field became therefore split into present Northern and Southern fields. At the second largest lake of South America, the Buenos Aires-General Carrera Lake, the water level dropped from about 500 m over present mean sea level to 230 m. Several glaciolacustrine deposits from this area are indicating significant variations caused by climatic changes, volcanism and tectonics, differing in spatial and temporal magnitudes. The triple junction activity involved subduction of the Chile Ridge below the continental South American plate, volcanic activity and faulting. During the glacier melting the Baker River captured three eastern-moving glacial systems towards the southwest, towards the Pacific Ocean. This rapid event is thought to occur 12,800 yrs BP. The lowering of these glaciolacustrine systems should be also interpreted in terms of the tectonic activity in the region and considering other processes operating in the lakes and within the watersheds.pp.94-10
Las Quínoas oncoids: a new deposit of microbialites in the Salar de Antofalla (Catamarca, Argentina)
No full textThe Salar de Antofalla (salt flat) is located in the Puna region of Catamarca, in northern Argentina. In this paper we report and provide the first descriptive data of Las Quínoas, a modern system of oncoids located in the western margin of the salt flat. Oncoids were studied by insitu logging, polished and thin sections analysis. In addition, the 16s rRNA genes of microbial mats associated with these oncoids were amplified and sequenced to characterize the microbial biodiversity. Oncoids present discoidal to subrounded morphologies and sizes up to 15 cm in diameter. They are scattered along channels, which originate from the groundwater springs of a wetland and enter the salt flat. Its macrostructure is concentric and composed by three zones: 1. A nucleus zone built by clastic material in a carbonate matrix. 2. A well-laminated zone around the nucleus that shows two types of mesostructures: concentrically stacked spheroids (SS-C) and randomly stacked hemispheroids (SS-R), both showing an alternation of dense and dark micritic laminae with light micritic to microsparitic laminae. 3. A poorly-laminated zone, in the outermost sector of oncoids, with two types of mesostructures too: a laminated mesostructure composed also of an alternation of dense and dark micritic laminae with light micritic to microsparitic laminae, and a non-laminated mesostructure composed of agglomerated and cemented clastic material within a calcareous matrix (wackestones-packstones). Regarding the microbial diversity, the analyzed oncoids in this work are mainly inhabited by Proteobacteria (ca. 37.5%), Bacteroidetes (ca. 25.0%), and in less proportion Planctomycetes, Actinobacteria and Cyanobacteria.pp.281-30