Examinando por Materia "volcanism"
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Ítem Community participation in natural risk prevention: Case histories from Colombia(GEOLOGICAL SOC PUBLISHING HOUSE, 2008-01-01) Hermelin, M.; Bedoya, G.; Universidad EAFIT. Departamento de Geología; Ciencias del MarMore than 75% of Colombia's 42 million people live in urban areas located in the mountains and are exposed to numerous natural hazards: floods, flash floods, landslides, earthquakes and volcanism. The Armero disaster of 1985 triggered the creation of the National System for Disaster Prevention and Relief. National, regional and local committees started to operate across the country, accompanied by education commissions that produced diverse audiovisual materials to help educate people living in these areas. The experiences of working with local committees gained during the last two decades are presented here. Case histories are from cities such as Pereira, Manizales and Medellín, where the local committees are run by people with little or no formal education but who understand that they must participate as a group to prevent or mitigate the effects of natural disasters. The co-operation between technical experts and trained residents represents an outstanding example of good communication and co-operation for urban populations living in dangerous areas. Although many problems have yet to be resolved, these case histories show that this type of organization seems to be more effective than direct intervention from national government agencies. The models of community participation and communication developed and refined here may have application to similar social environments in other countries. © 2008 Geological Society of London.Ítem Community participation in natural risk prevention: Case histories from Colombia(GEOLOGICAL SOC PUBLISHING HOUSE, 2008-01-01) Hermelin, M.; Bedoya, G.; Hermelin, M.; Bedoya, G.; Universidad EAFIT. Departamento de Ciencias; Geología Ambiental y TectónicaMore than 75% of Colombia's 42 million people live in urban areas located in the mountains and are exposed to numerous natural hazards: floods, flash floods, landslides, earthquakes and volcanism. The Armero disaster of 1985 triggered the creation of the National System for Disaster Prevention and Relief. National, regional and local committees started to operate across the country, accompanied by education commissions that produced diverse audiovisual materials to help educate people living in these areas. The experiences of working with local committees gained during the last two decades are presented here. Case histories are from cities such as Pereira, Manizales and Medellín, where the local committees are run by people with little or no formal education but who understand that they must participate as a group to prevent or mitigate the effects of natural disasters. The co-operation between technical experts and trained residents represents an outstanding example of good communication and co-operation for urban populations living in dangerous areas. Although many problems have yet to be resolved, these case histories show that this type of organization seems to be more effective than direct intervention from national government agencies. The models of community participation and communication developed and refined here may have application to similar social environments in other countries. © 2008 Geological Society of London.Ítem Hydrogeochemical characteristics at Doña Juana Complex (SW Colombia): A new area for geothermal exploration in the Northern Andes region(Elsevier Ltd., 2020-01-01) Gómez Diaz E.; Marín Cerón M.I.; Gómez Diaz E.; Marín Cerón M.I.; Universidad EAFIT. Departamento de Ciencias; Geología Ambiental y TectónicaThe Doña Juana Volcanic Complex (DJVC) is an active volcanic zone located in southern Colombia, an area lacking geothermal exploration data. Using the results of hydrogeochemical analyses of hot springs, thermal waters were divided into two groups: Doña Juana System (DJS) and Las Animas System (AS). The DJS thermal waters are sulphate-bicarbonate and the AS dilute-chloride waters with relatively high concentrations of alkalis. The stable isotope and some element ratios suggested a mixing process between geothermal fluids and meteoric waters where AS is related to the upflow with a reservoir temperature around 180 °C estimated through solute geothermometers and mineral equilibrium geothermometry, showing a high temperature system in which the fault systems apparently play an important role in the flow of the geothermal fluids. © 2019 Elsevier LtdÍtem Tectonic and climate driven fluctuations in the stratigraphic base level of a Cenozoic continental coal basin, northwestern Andes(PERGAMON-ELSEVIER SCIENCE LTD, 2008-12-01) Tamayo, J. C. Silva; Sierra, G. M.; Correa, L. G.; Tamayo, J. C. Silva; Sierra, G. M.; Correa, L. G.; Universidad EAFIT. Departamento de Ciencias; Geología Ambiental y TectónicaChanges in the sedimentologic and stratigraphic characteristics of the coal-bearing middle Oligocene-late Miocene siliciclastic Amagá Formation, northwestern Colombia, reflect major fluctuations in the stratigraphic base level within the Amagá Basin, which paralleled three major stages of evolution of the middle Cenozoic Andean Orogeny. These stages, which are also traceable by the changes in the compositional modes of sandstones, controlled the occurrence of important coal deposits. The initial stage of evolution of the Amagá Basin was related to the initial uplift of the Central Cordillera of Colombia around 25 Ma, which promoted moderate subsidence rates and high rates of sediment supply into the basin. This allowed the development of aggradational braided rivers and widespread channel amalgamation resulting in poor preservation of both, low energy facies and geomorphic elements. The presence of poorly preserved Alfisols within the scarce flood plains and the absence of swamp deposits suggest arid climate during this stage. The compositional modes of sandstones suggest sediment supply from uplifted basement-cored blocks. The second stage of evolution was related to the late Oligocene eastward migration of the Pre-Andean tholeitic magmatic arc from the Western Cordillera towards the Cauca depression. This generated extensional movements along the Amagá Basin, enhancing the subsidence and increasing the accommodation space along the basin. As a result of the enhanced subsidence rates, meandering rivers developed, allowing the formation of extensive swamps deposits (currently coal beds). The excellent preservation of Entisols and Alfisols within the flood plain deposits suggests rapid channels migration and a humid climate during deposition. Moderate to highly mature channel sandstones support this contention, and point out the Central Cordillera of Colombia as the main source of sediment. Enhanced subsidence during this stage also prevented channels amalgamation and promoted both, high preservation of geomorphic elements and high diversity of sedimentary facies. This resulted in the most symmetric stratigraphic cycles of the entire Amagá Formation. The final stage of evolution of the Amagá Basin was related to the early stage of development of the late Miocene northwestern Andes tholeitic volcanism (from ~10 to ~8 Ma). The extensive thrusting and folding associated to this volcanism reduced the subsidence rates along the basin and thus the accommodation space. This permitted the development of highly aggradational braided rivers and promoted channels amalgamation. Little preservation of low energy facies, poor preservation of the geomorphic elements and a complete obliteration of important swamp deposits (coal beds) within the basin are reflected by the most asymmetric stratigraphic cycles of the whole formation. The presence of greenish/reddish flood plain deposits and Alfisols suggests a dry climate during this depositional stage. The presence of channel sandstones with high contents of volcanic rock fragments supports a dry climate, and suggests an incipient phase of the Combia tholeiitic magmatism present during deposition of the Amagá Formation. The subsequent eastward migration of the NW Andes magmatic arc (after ~8 Ma) may have produced basin inversion and suppressed deposition along the Amagá Basin. © 2008 Elsevier Ltd. All rights reserved.