Processes, time scales and unrest of monogenetic volcanism

[eng] Seismic, deformation, and gas activity (unrest) typically precedes volcanic eruptions. Successful volcanic event forecasting depends on the quality of the surveillance network for detecting any changes in volcano behaviour. To interpret the geochemical and geophysical precursors correctly it is important to understand the volcanic processes that occur prior and during volcanic eruptions. Detailed knowledge of the volcano internal structure, the rheology of the magmas, the time scales of the processes occurring at depth and the characteristics of past unrest episodes, must be combined with an adequate monitoring network to improve the volcanic hazard forecast. However, these aspects have received little attention in monogenetic volcanoes. The aim of my PhD Thesis is to improve our understanding on monogenetic volcanism, its causes and dynamics, and to help anticipating the volcanic activity. I have focused on three main aspects of this problem. The first one is the calculation of the rheological properties of magmas during mixing. The second aspect I have addressed are the processes and time scales that lead to monogenetic eruptions with the aim to better interpret volcanic unrest and improve eruption forecasts. Finally, I have investigated the seismic unrest periods of historical monogenetic eruptions from a compilation of historical accounts worldwide. The results provide a conceptual framework for better anticipating monogenetic eruptions and should lead to improved strategies for mitigation of their associated hazards and risks.[spa] Las erupciones volcánicas están generalmente precedidas por la actividad sísmica, la deformación y la desgasificación (unrest). El éxito en la predicción del evento volcánico depende de la calidad de la red de vigilancia para detectar cualquier cambio en el comportamiento del volcán. Para interpretar los precursores geoquímicos y geofísicos correctamente es importante entender los procesos volcánicos que ocurren antes y durante las erupciones volcánicas. El conocimiento en detalle de la estructura interna del volcán, la reología de los magmas, las escalas de tiempo de los procesos que ocurren en profundidad y las características de los episodios pasados de unrest, debe combinarse con una red de vigilancia adecuada para mejorar el pronóstico de los eventos volcánicos. Sin embargo, estos aspectos han recibido poca atención en los volcanes monogenéticos. El objetivo de mi tesis doctoral es mejorar nuestra comprensión sobre el vulcanismo monogenético, sus causas y su dinámica, con el objetivo de mejorar la posibilidad de anticiparse a la actividad volcánica. Me he centrado en tres aspectos principales de este problema. El primero es el cálculo de las propiedades reológicas de los magmas durante los eventos de mezcla. El segundo aspecto es el estudio de los procesos, junto con sus escalas temporales, que llevan a erupciones monogenéticas con el fin de interpretar mejor la actividad volcánica y mejorar los pronósticos de una erupción. Por último, he investigado los períodos de unrest sísmico de erupciones monogenéticas históricas en todo el mundo mediante una compilación de documentos históricos. Los resultados proporcionan un marco conceptual que permite mejorar la predicción de erupciones monogenéticas y deberían conducir a mejores estrategias para mitigar sus peligros y riesgos asociados

Characterization of the Outer Coast Tuff Formation - A way to unravelling the magmatic processes preceding and triggering Deception Island's caldera-forming eruption (Antarctica)

Deception Island (South Shetland Islands), discovered in 1820, is one of the most active volcanoes in Antarctica with more than 20 eruptions (including the historic eruptions of 1967, 1969 and 1970) and three documented volcanic unrest events (1992, 1999 and 2014-15) over the past two centuries. Deception Island currently hosts two scientific bases, which operate every year during the Austral summer, and is also one of the most popular tourist destinations in Antarctica. The island is a composite volcano with a centrally located caldera of 8.5 x 10 km dated at 3,980 ± 125 yr. BP. During the caldera-forming event, between 30 and 60 km3 (Dense Rock Equivalent-DRE) of magma, erupted in the form of dense basaltic-andesitic pyroclastic density current deposits. During the last decades, Deception Island has been intensively investigated but some aspects regarding the magmatic processes associated with the formation of its caldera collapse are still under research and debate. For instance, characterizing the magmatic conditions and processes that triggered the huge explosive event is crucial to understand the past (and in turn the future) magmatic and volcanic evolution of the island

Descifrando los procesos magmáticos desencadenantes de la formación de la caldera en Isla Decepción (Antártida)

Isla Decepción (Islas Shetland del Sur) es uno de los volcanes más activos de la Antártida, con más de 20 erupciones en los últimos 200 años (las más recientes en 1967, 1969 y 1970) y tres episodios de unrest documentados (1992, 1999 y 2014-15). La isla está formada por un sistema volcánico compuesto con una caldera central de 8,5 x 10 km datada en unos 3.980 ± 125 años. Durante la formación de la caldera de colapso, se emitieron entre 30 y 60 km3 (Dense Rock Equivalent-DRE) de magma basáltico-andesítico en forma de flujos piroclásticos, que dieron lugar a la Outer Coast Tuff Formation (OCTF), la principal unidad sin-caldera. Caracterizar las condiciones magmáticas y los procesos que desencadenaron el evento explosivo es crucial para entender el pasado (y futuro) de la evolución magmática de la isla. El objetivo de este trabajo es establecer, a partir de la petrología y la geoquímica, las condiciones y los procesos magmáticos que tuvieron lugar antes y durante la formación de la caldera de colapso. Los resultados preliminares confirman la existencia de dos magmas coexistiendo e interactuando antes (y durante) la erupción caldérica y procesos de cristalización fraccionada. Esta investigación es parte de las iniciativas de investigación POLARCSIC y PTIVolcan

Mineralogy of the Hydrothermal Alteration in the Námafjall Geothermal Field (Iceland)

Present-day rift zones in Iceland commonly develop high-temperature geothermal systems related to central volcanoes (Trønnes, 2003). This study was developed at the high-temperature geothermal field of Námafjall, located at the Iceland Northern Rift Zone, near the Krafla central volcano. In this area, the constant hydrothermal activity alters Pleistocene hyaloclastites sequences and Holocene lavas and scoria cones especially to clay minerals. Different degrees of alteration, anisotropic distribution of fissures, faults and permeable zones, and accumulation of different minerals, generates a spotty distribution of red, brown, yellow, pink and white patches, reflecting the mosaic character of hydrothermal alteration (Geptner et al., 2005, 2007). A detailed mineralogical study of the altered volcanic rocks from the outer edge of the Námafjall geothermal field has been carried out in order to determine the surface alteration processes associated with geothermal activity, inferring pH conditions and, where appropriate, the temperature of the alteration processes.Peer reviewe

Identifying metamorphic rocks with the help of the petrographic microscope

El metamorfismo es un proceso que tiene lugar en el interior de la corteza y el manto superior, generalmente asociado a los límites de placas tectónicas, y que da lugar a la formación de rocas metamórficas. Este proceso se caracteriza por un conjunto de cambios en la textura y la mineralogía, en el estado sólido, que experimenta cualquier roca sometida a condiciones de presión y temperatura diferentes a las de su formación, excluyendo los procesos diagenéticos propios de rocas sedimentarias. La clasificación de las rocas metamórficas resulta bastante compleja ya que están constituidas por una gran variedad de minerales y de texturas que a menudo requieren ser identificados con la ayuda del microscopio petrográfico. En las aulas de Secundaria y Bachillerato siempre es un reto para el profesorado la enseñanza de estas rocas. Por ello, en este trabajo se describen los aspectos más relevantes a cerca del metamorfismo y se propone una actividad didáctica la cual incluye fichas de apoyo a la identificación del tipo de metamorfismo y los grupos composicionales y 13 descripciones de rocas metamórficas en lámina delgada

Las rocas ígneas en el microscopio petrográfico. Estrategias y recursos para su aprendizaje

En este documento se incluyen distintos archivos que forman parte del artículo "Las rocas ígneas en el microscopio petrográfico. Estrategias y recursos para su aprendizaje". los archivos contienen: (1) microfotografías de rocas ígneas realizadas al microscopio petrográfico, (2) catorze fichas descriptivas de rocas ígneas, (3) archivo .kmz para ser visualizado a través de Google Earth. Este documento se irá ampliando progresivamente con la inclusión de nuevas microfotografías y fichas, así como la actualitzación del archivo .km

Stoma-free survival after anastomotic leak following rectal cancer resection: worldwide cohort of 2470 patients

Background: The optimal treatment of anastomotic leak after rectal cancer resection is unclear. This worldwide cohort study aimed to provide an overview of four treatment strategies applied. Methods: Patients from 216 centres and 45 countries with anastomotic leak after rectal cancer resection between 2014 and 2018 were included. Treatment was categorized as salvage surgery, faecal diversion with passive or active (vacuum) drainage, and no primary/secondary faecal diversion. The primary outcome was 1-year stoma-free survival. In addition, passive and active drainage were compared using propensity score matching (2: 1). Results: Of 2470 evaluable patients, 388 (16.0 per cent) underwent salvage surgery, 1524 (62.0 per cent) passive drainage, 278 (11.0 per cent) active drainage, and 280 (11.0 per cent) had no faecal diversion. One-year stoma-free survival rates were 13.7, 48.3, 48.2, and 65.4 per cent respectively. Propensity score matching resulted in 556 patients with passive and 278 with active drainage. There was no statistically significant difference between these groups in 1-year stoma-free survival (OR 0.95, 95 per cent c.i. 0.66 to 1.33), with a risk difference of -1.1 (95 per cent c.i. -9.0 to 7.0) per cent. After active drainage, more patients required secondary salvage surgery (OR 2.32, 1.49 to 3.59), prolonged hospital admission (an additional 6 (95 per cent c.i. 2 to 10) days), and ICU admission (OR 1.41, 1.02 to 1.94). Mean duration of leak healing did not differ significantly (an additional 12 (-28 to 52) days). Conclusion: Primary salvage surgery or omission of faecal diversion likely correspond to the most severe and least severe leaks respectively. In patients with diverted leaks, stoma-free survival did not differ statistically between passive and active drainage, although the increased risk of secondary salvage surgery and ICU admission suggests residual confounding

Stoma-free Survival After Rectal Cancer Resection With Anastomotic Leakage: Development and Validation of a Prediction Model in a Large International Cohort.

Objective:To develop and validate a prediction model (STOMA score) for 1-year stoma-free survival in patients with rectal cancer (RC) with anastomotic leakage (AL).Background:AL after RC resection often results in a permanent stoma.Methods:This international retrospective cohort study (TENTACLE-Rectum) encompassed 216 participating centres and included patients who developed AL after RC surgery between 2014 and 2018. Clinically relevant predictors for 1-year stoma-free survival were included in uni and multivariable logistic regression models. The STOMA score was developed and internally validated in a cohort of patients operated between 2014 and 2017, with subsequent temporal validation in a 2018 cohort. The discriminative power and calibration of the models' performance were evaluated.Results:This study included 2499 patients with AL, 1954 in the development cohort and 545 in the validation cohort. Baseline characteristics were comparable. One-year stoma-free survival was 45.0% in the development cohort and 43.7% in the validation cohort. The following predictors were included in the STOMA score: sex, age, American Society of Anestesiologist classification, body mass index, clinical M-disease, neoadjuvant therapy, abdominal and transanal approach, primary defunctioning stoma, multivisceral resection, clinical setting in which AL was diagnosed, postoperative day of AL diagnosis, abdominal contamination, anastomotic defect circumference, bowel wall ischemia, anastomotic fistula, retraction, and reactivation leakage. The STOMA score showed good discrimination and calibration (c-index: 0.71, 95% CI: 0.66-0.76).Conclusions:The STOMA score consists of 18 clinically relevant factors and estimates the individual risk for 1-year stoma-free survival in patients with AL after RC surgery, which may improve patient counseling and give guidance when analyzing the efficacy of different treatment strategies in future studies