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451 results on '"Alvarado, Guillermo E."'

203. Emisión difusa de dióxido de carbono en el Volcán Irazú, Costa Rica

Author

Galindo, Inés, primary, Melián, Gladys V., additional, Salazar, José M.L., additional, Hernández, Pedro A., additional, Pérez, Nemesio M., additional, Ramírez, Carlos, additional, Fernández, Mario, additional, Alvarado, Guillermo E., additional, Sumino, Hirochika, additional, and Notsu, Kenji, additional

Published
2011
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231. Geología de la hoja San Isidro, Costa Rica

Author

Alvarado, Guillermo E., primary, Barquero, Rafael, additional, Taylor, Waldo, additional, Mora, Mauricio, additional, Peraldo, Giovanni, additional, Salazar, Guillermo, additional, and Aguilar, Teresita, additional

Published
2008
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248. LA ACTIVIDAD EXPLOSIVA DEL VOLCÁN TURRIALBA (COSTA RICA) EN EL PERÍODO 2010 - 2016.

Author

Alvarado, Guillermo E., Brenes-André, José, Barrantes, Manuel, Vega, Eduardo, de Moor, J. Maarten, Avard, Geoffroy, Dellino, Pierfrancesco, Mele, Daniela, DeVitre, Charlotte, Di Piazza, Andrea, Rizzo, Andrea L., and Carapezza, Maria L.

Subjects
*VOLCANOES, *VOLCANIC eruptions, *VOLCANIC ash, tuff, etc.
Abstract

The most recent eruptive activity of Turrialba volcano began on the 5th of January 2010, after more than a century of dormancy. The fragmentation process and aerodynamic behavior of the ash from Turrialba’s vulcanian eruptions were investigated by combining grain-size, petrography, mineralogy, Scanning Electron Microscopy (SEM) and Energy Dispersive System (EDS) analyses. The ash components include variable percentages of accessory fresh (no necessary juvenile) to hydrothermally altered lithics (15 - 50 % vol.) with hydrothermal minerals (≤ 12 % vol.: anhydrite, gypsum, bassanite, alunite, hexahydrite, pyrite, heulandite, native sulfur), clay minerals (8 - 17 % vol.: montmorillonite, halloysite, allophane), and a smaller quantity of fresh glassy ashes (5 - 49 % vol.) as fragments and shards (3 - 20 % vol. tackylite and 2 - 26 % vol. sideromelane), as well as primary and eroded/recycled phenocrysts (3 - 13 % vol.: 1 - 5% vol. plagioclase, 1 - 7 % vol. pyroxene, 0 - 1 % vol. olivine, 0 - 6 % vol. opaques, cristobalite and tridimite), and xenocrysts (≤ 1 % vol.: riebeckite and biotite). The secondary minerals were sourced from the deeper to surficial hydrothermal system. Textural features identified in ash particles (90 - 350 μm) suggest that they were formed by brittle fragmentation of vesicle-poor magma/water interaction; molten structures seems to be related to the ductile behavior of some fragments, probably due to the high temperature (> 600 °C) of the fumarolic/magmatic system. The percentage of juvenile components was low (1 - 2 % vol.) at the first opening eruptive phase in January 2010, and it increased steadily until the end of 2016 (ca. 12 - 25 % vol.) . The ash eruptions in the Western Crater from 2014 to 2016 were related to one and later two or three simultaneously active vents fed by distinct conduit branches. The alternation of volcanic explosions (VEI: 0 - 2), from closed conduit and the formation of new craters, to open system with phreatomagmatic events, and the repose intervals (inter-eruptive exhalative degassing), were controlled by the rate at which magma ascended and remained in the volcanic edifice. The recent tephra sequence consists of a complex succession of layers generated by contrasting fragmentation and transportation dynamics. They resulted from fully diluted, low temperature (< 300 °C), pyroclastic density currents (wet surge deposits), originated by short-lived, singlepulse, column collapse of phreatomagmatic columns, which traveled short distances (< 1000 m) from the vent area and surmounted topographic obstacles, and simultaneous fallout and ballistic ejecta. The fine material, in continuous suspension within the uppermost part of the convective plume, was dispersed into the atmosphere and finally settled down on the Valle Central. The quiescent phases could be related to a temporal cooling of the magmatic dike system or to a waning of magmatic activity at depth. Sequential fragmentation/transport theory (SFT) was used to decompose grain-size distributions into five different sub-populations. A new way of using the resultant fragmentation coefficient to assign sub-populations to different fragmentation mechanisms, even in cases when modes overlapped, is presented. For the first time the corresponding results are consistent with the phreatomagmatic eruptions, as well as with those derived from ab initio fractal model. [ABSTRACT FROM AUTHOR]

Published
2016
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249. Características geológicas de la Estación Biológica La Selva, Costa Rica

Author

Alvarado, Guillermo E. and Alvarado, Guillermo E.

Abstract

En los alrrededores de Puerto Viejo de Sarapiquí (Heredia) aflora una estrecha secuencia espacial y temporal de lavas subalcalinas y medianamente alcalinas. La Formación Andesitas Sarapiquí (Plioceno) está representada por andesitas y andesitas basálticas presentes en los Cerros Sardinal y Arrepentidos. En la Estación Biológica La Selva, se analizaron tres unidades litológicas del Pleistoceno Inferior: Basaltos ligeramente alcalinos "Vargas", Andesitas basálticas "El Salto" y Andesitas "Esquina" (datada en un millón doscientos mil años). Petroquímicamente, las lavas de"La Selva" son ligeramente diferentes a la de los grandes estratovolcanes cuaternarios de la Cordillera Central. Están parcialmente cubiertas por depósitos aluviales y palustres del Cuaternario Superior con varias terrazas fluviales. Los suelos de los Cerros Arrepentidos-Sardinal son macroscópicamente diferentes a los de "La Selva, debido probablemente a que se desarrollaron bajo condiciones cilmáticas diferentes.

Published
1990

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