41 research outputs found
Lithostratigraphic analysis and geochemistry of a vitric spatter-bearing ignimbrite: the Quaternary Adeje Formation, Cañadas volcano, Tenerife
"The 1.5-Ma Adeje Formation in SW Tenerife contains an ignimbrite sheet with remarkable textural and chemical complexity. A basal Plinian pumice-fall layer is overlain by a partly welded compound ignimbrite in which phonolitic pumice lapilli and dense obsidian spatter rags with irregular, fluidal-shaped margins are supported in a poorly sorted tuff matrix. The lower ignimbrite flow-unit contains accretionary lapilli in its upper part, overlain by an ash-pellet-bearing fallout layer from a co-ignimbrite plume. The upper ignimbrite flow-unit comprises a locally welded massive lapilli-tuff that grades up into lithic breccia containing juvenile obsidian blocks and both cognate and vent-derived lithic blocks. Geochemically, the Adeje Formation shows two distinct juvenile populations that relate to crystal-poor and crystal-rich magma types. Crystal-rich juvenile clasts contain multiple compositions of ilmenite and magnetite, and crystal aggregates of bytownite (An79-86). The varied assemblage of juvenile clasts reflects an eruptive style that may have involved rapid changes in magma chamber pressure associated with caldera collapse, and possibly the disruption of a lava lake. The Adeje eruption started with a Plinian explosive phase that rained ash and pumice lapilli across SW Tenerife; followed by pyroclastic fountaining feeding density currents with explosive ejecta of juvenile glassy material producing the coarse, spatter-bearing ignimbrite facies. A short pause between pyroclastic density currents is recorded by the co-ignimbrite ash and pellet-fall bed. The climactic phase of the eruption probably involved caldera subsidence as recorded by a widespread massive heterolithic breccia.
How Polygenetic are Monogenetic Volcanoes: Case Studies of Some Complex MaarâDiatreme Volcanoes
The increasing number of field investigations and various controlled benchtop and largeâscale experiments have permitted the evaluation of a large number of processes involved in the formation of maarâdiatreme volcanoes, the second most common type of smallâvolume subaerial volcanoes on Earth. A maarâdiatreme volcano is recognized by a volcanic crater that is cut into country rocks and surrounded by a lowâheight ejecta rim composed of pyroclastic deposits of few meters to up to 200âm thick above the synâeruptive surface level. The craters vary from 0.1âkm to up to 5âkm wide and vary in depth from a few dozen meters to up to 300âm deep. Their irregular morphology reflects the simple or complex volcanic and cratering processes involved in their formation. The simplicity or complexity of the crater or the entire maar itself is usually observed in the stratigraphy of the surrounding ejecta rings. The latter are composed of sequences of successive alternating and contrastingly bedded phreatomagmaticâderived dilute pyroclastic density currents (PDC) and fallout depositions, with occasional interbedded Strombolianâderived spatter materials or scoria fall units, exemplifying the changes in the eruptive styles during the formation of the volcano. The entire stratigraphic sequence might be preserved as a single eruptive package (small or very thick) in which there is no stratigraphic gap or significant discordance indicative of a potential break during the eruption. A maar with a single eruptive deposit is quantified as monogenetic maar, meaning that it was formed by a single eruptive vent from which only a small and ephemeral magma erupted over a short period of time. The stratigraphy may also display several packages of deposits separated either by contrasting discordance surfaces or paleosoils, which reflect multiple phases or episodes of eruptions within the same maar. Such maars are characterized as complex polycyclic maars if the length of time between the eruptive events is relatively short (days to years). For greater length of time (thousands to millions of years), the complex maar will be quantified as polygenetic. These common depositional breaks interpreted as signs of temporal interruption of the eruptions for various timescales also indicate deep magma system processes; hence magmas of different types might erupt during the formation of both simple and complex maars. The feeding dikes can interact with groundwater and form closely distributed small craters. The latter can coalesce to form a final crater with various shapes depending on the distance between them. This observation indicates the significant role of the magmatic plumbing system on the formation and growth of complex and polygenetic maarâdiatreme volcanoes
AnĂĄlisis crĂtico de las facultades probatorias de las partes en segunda instancia en el proceso civil chileno
This article makes a critical analysis about the regulation contemplated in the civil procedure code regarding the means of proof whose initiative corresponds to parties during the processing of the second instance. The evaluator of this regulation will be the burden of objective proof, which includes certain objectives in good procedural faith. It is argued that the possibility of testing in the second instance allows strategic behaviors and a divergence between public and private interests. Therefore, the presentation of evidence in that instance must be limited to the existence of new facts. The latter is more in line with the review purpose of the appeal.El presente artĂculo realiza un anĂĄlisis crĂtico de la regulaciĂłn contemplada en el cĂłdigo de procedimiento civil de los medios probatorios cuya iniciativa corresponde a las partes durante la segunda instancia. El evaluador de dicha regulaciĂłn serĂĄ la carga de prueba objetiva, la que comprende ciertos objetivos de buena fe procesal. Se sostiene que la posibilidad de rendir prueba en segunda instancia permite comportamientos estratĂ©gicos y una divergencia entre los intereses pĂșblicos y privados. Por tanto, la presentaciĂłn de prueba en esa instancia debe limitarse a la existencia de hechos nuevos. Esto Ășltimo es mĂĄs acorde con la finalidad revisora del recurso de apelaciĂłn.
 
The impact of hydrothermal alteration on the physiochemical characteristics of reservoir rocks: the case of the Los Humeros geothermal field (Mexico)
Hydrothermal alteration is a common process in active geothermal systems and can significantly change the physiochemical properties of rocks. To improve reservoir assessment and modeling of high-temperature geothermal resources linked to active volcanic settings, a detailed understanding of the reservoir is needed. The Los Humeros Volcanic Complex, hosting the third largest exploited geothermal field in Mexico, represents a natural laboratory to investigate the impact of hydrothermal processes on the rock properties through andesitic reservoir cores and outcropping analogs. Complementary petrographic and chemical analyses were used to characterize the intensities and facies of hydrothermal alteration. The alteration varies from argillic and propylitic facies characterized by no significant changes of the REE budget indicating an inert behavior to silicic facies and skarn instead showing highly variable REE contents. Unaltered outcrop samples predominantly feature low matrix permeabilities (â1.67Â WÂ mâ1Â Kâ1;â>â0.91Â 10â6Â m2Â sâ1), but a significant loss of magnetic susceptibility (10â3â10â6 SI). In particular, this latter characteristic appears to be a suitable indicator during geophysical survey for the identification of hydrothermalized domains and possible pathways for fluids. The lack of clear trends between alteration facies, alteration intensity, and chemical indices in the studied samples is interpreted as the response to multiple and/or repeated hydrothermal events. Finally, the proposed integrated field-based approach shows the capability to unravel the complexity of geothermal reservoir rocks in active volcanic settings
Contrapicados y puntos de fuga. Las otras historias de la historia de la filosofĂa
Depto. de LĂłgica y FilosofĂa TeĂłricaFac. de FilosofĂaFALSEsubmitte
Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries
Abstract
Background
Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres.
Methods
This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and lowâmiddle-income countries.
Results
In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of âsingle-useâ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for lowâmiddle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia.
Conclusion
This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both highâ and lowâmiddleâincome countries
Stratigraphy of the 8.5 - 9.0 ka B.P. Citlaltépetl pumice fallout sequence
Citlaltépetl is an active volcano presently in a dormant state, belonging to the easternmost part of the Mexican Volcanic Belt. Although the volcano is characterized by long periods of volcanic repose, some explosive plinian eruptions occurred in Holocene time. In particular, an eruptive period between 8.5-9.0 ka B.P. originated an alternated sequence of pumice and scoria flows called Citlaltépetl Ignimbrite (0.26 km3 DRE) and a few ash and lapilli fallout deposits (Citlaltépetl Pumice) with a wide dispersion range around the cone. In this work we present a detailed reconstruction of the fallout Citlaltépetl Pumice stratigraphy based on the combined study of 107 vertical sections, grain-size and component analysis of each layer. The eruptive sequence comprises a succession of pyroclastic deposits, including four major eruptive episodes. New radiocarbon dating on charcoal fragments interbedded in the flow deposits beneath the fallout and in the fallout itself show ages younger than 9,475±160 yr. B.P. and older than 8,505±50 yr. B.P., respectively, which is in accordance with previous dates. Stratigraphy and dating allowed a precise stratigraphic correlation of the most representative fallout deposits of the Holocene history of Citlaltépetl volcano and their relationship with associated pyroclastic flows. Such data provide new insights on the formation and eruptive history of the Citlaltépetl Ignimbrite that is of basic importance for further eruptive column modeling with important implications in the volcanic hazard assessment
Stratigraphy of the 8.5 - 9.0 ka B.P. Citlaltépetl pumice fallout sequence
Citlaltépetl is an active volcano presently in a dormant state, belonging to the easternmost part of the Mexican Volcanic Belt. Although the volcano is characterized by long periods of volcanic repose, some explosive plinian eruptions occurred in Holocene time. In particular, an eruptive period between 8.5-9.0 ka B.P. originated an alternated sequence of pumice and scoria flows called Citlaltépetl Ignimbrite (0.26 km3 DRE) and a few ash and lapilli fallout deposits (Citlaltépetl Pumice) with a wide dispersion range around the cone. In this work we present a detailed reconstruction of the fallout Citlaltépetl Pumice stratigraphy based on the combined study of 107 vertical sections, grain-size and component analysis of each layer. The eruptive sequence comprises a succession of pyroclastic deposits, including four major eruptive episodes. New radiocarbon dating on charcoal fragments interbedded in the flow deposits beneath the fallout and in the fallout itself show ages younger than 9,475±160 yr. B.P. and older than 8,505±50 yr. B.P., respectively, which is in accordance with previous dates. Stratigraphy and dating allowed a precise stratigraphic correlation of the most representative fallout deposits of the Holocene history of Citlaltépetl volcano and their relationship with associated pyroclastic flows. Such data provide new insights on the formation and eruptive history of the Citlaltépetl Ignimbrite that is of basic importance for further eruptive column modeling with important implications in the volcanic hazard assessment
Stratigraphy of the 8.5 - 9.0 ka B.P. Citlaltépetl pumice fallout sequence
Citlaltépetl is an active volcano presently in a dormant state, belonging to the easternmost part of the Mexican Volcanic Belt. Although the volcano is characterized by long periods of volcanic repose, some explosive plinian eruptions occurred in Holocene time. In particular, an eruptive period between 8.5-9.0 ka B.P. originated an alternated sequence of pumice and scoria flows called Citlaltépetl Ignimbrite (0.26 km3 DRE) and a few ash and lapilli fallout deposits (Citlaltépetl Pumice) with a wide dispersion range around the cone. In this work we present a detailed reconstruction of the fallout Citlaltépetl Pumice stratigraphy based on the combined study of 107 vertical sections, grain-size and component analysis of each layer. The eruptive sequence comprises a succession of pyroclastic deposits, including four major eruptive episodes. New radiocarbon dating on charcoal fragments interbedded in the flow deposits beneath the fallout and in the fallout itself show ages younger than 9,475±160 yr. B.P. and older than 8,505±50 yr. B.P., respectively, which is in accordance with previous dates. Stratigraphy and dating allowed a precise stratigraphic correlation of the most representative fallout deposits of the Holocene history of Citlaltépetl volcano and their relationship with associated pyroclastic flows. Such data provide new insights on the formation and eruptive history of the Citlaltépetl Ignimbrite that is of basic importance for further eruptive column modeling with important implications in the volcanic hazard assessment