Papers by Eduardo Malavassi
Bulletin of Volcanology, 2002
The bulk composition of magma erupted from Volcán Arenal has remained nearly constant (SiO 2 = 53... more The bulk composition of magma erupted from Volcán Arenal has remained nearly constant (SiO 2 = 53.6-54.9 wt%; MgO = 5.0-4.5 wt%) during almost 30 years of continuous activity (1969-1996). None the less, clinopyroxene (cpx) phenocrysts and their spinel inclusions record a much more complex open-system evolution in which steady-state production of the erupted basaltic andesitic magma is linked to episodic injections of basalt into Arenal's magma conduit/reservoir system. High-resolution major element zoning profiles (electron microprobe) on a large number of phenocrysts (>14,000 analyses), tied to back-scattered electron (BSE) images, have been used to assess the compositional characteristics of the magmatic end members as well as the timing and dynamics of magma replenishment events. No two cpx phenocrysts have exactly the same zoning profile. The vast majority of our analyses record the crystallization of cpx (Cr 2 O 3 <0.12 wt%; Mg# = 65-79; Al/Ti = 2-7) from a liquid comparable to or more evolved than erupted magma compositions. However, half of all cpx grains are cored by high-Cr cpx (Cr 2 O 3 = 0.2-0.72 wt%) or contain similar basaltic compositions as abrupt growth bands in phenocrysts with and without high-Cr cores; phenocrysts with high-Cr cpx occur throughout the ongoing activity. In a few cases, high-Cr cpx occurs very near the outer margin of the grain without an apparent growth hiatus, particularly in 1968/69 and 1992/93. The main conclusions are: (1) all basaltic andesitic lavas erupted at Arenal during the ongoing activity that began in July, 1968, are the products of magma mixing, (2) clinopyroxenes record multiple replenishment events of basaltic magma in contrast to the near constancy of erupted bulk compositions, (3) some phenocrysts preserve records of multiple interactions with basaltic magmas requiring magmatic processes to operate on timescales shorter than residence times of some phenocrysts, (4) multiple occurrences of clinopyroxene with high-Cr rims suggest that basalt replenishment events have occurred with sub-decadal frequency and may predate eruption by months or less. From this we infer that Arenal volcano is underlain by a continuously active, smallvolume magmatic reservoir maintained in quasi-steady state by basalt recharge over several decades. The monotony of erupting Arenal magmas implies that fractionation, recharge, ascent, and eruption are well balanced in order for magmas to be essentially uniform while containing phenocrysts with vastly different growth histories at the time of eruption.
Revista Geográfica de América Central; Vol 1, No 15-16 (1983): Revista Geográfica de América Central N. 15-16; 211-219, Jan 22, 2013
XX Congreso Latinoamericano de Estudiantes de Ingeniería Química, 2014
Escuela de Ciencias Geográficas, 2013
Universidad Nacional, Costa RicaInstituto Tecnológico de Costa RicaEscuela de Ciencias Geográfica
Geo UERJ, 2013
El presente trabajo utiliza el modelo de Suzuki (Suzuki, 1983) para simular la caída de ceniza vo... more El presente trabajo utiliza el modelo de Suzuki (Suzuki, 1983) para simular la caída de ceniza volcánica en la versión TEPHRA (Connors, 1991). El programa TEPHRA modificado es sometido a prueba al simular exitosamente la distribución de ceniza de los eventos eruptivos mejor conocidos en el volcán Irazú, Costa Rica. Adicionalmente, la masa de ceniza acumulada por 52 simulaciones de diseño concuerda satisfactoriamente con la distribución de las isopacas de la ceniza depositada durante el periodo 1963-65 del volcán Irazú y relativamente bien con la distribución de isopacas de la ceniza depositada durante los últimos 2600 años de actividad. Esta situación justifica la aplicación del programa TEPHRA modificado en la elaboración de mapas de amenaza por caída de ceniza para el Volcán Irazú y otros volcanes en los cuales se tenga apropiada información sobre dirección del viento y características eruptivas más probables de presentarse en el volcán.
Volcanic hazard in the form of ash deposition after eruptive processes is a constant element in t... more Volcanic hazard in the form of ash deposition after eruptive processes is a constant element in the geological history of Costa Rica and other countries in the Pacific Rim. TEPHRA, a program developed by Charles Connor at USF has been adapted and extended to consider a thoroughout evaluation of risk scenarios departing from physical variables. NG-TEPHRA is an ongoing project with the goal of using the PRAGMA Grid as an applications testbed for large-scale, highly detailed ash fall simulations leading to hazard assessment, disaster management and urban planning.
El Parque Nacional Isla del Coco, en Costa Rica, fue visitado por espacio de cinco dias, en el an... more El Parque Nacional Isla del Coco, en Costa Rica, fue visitado por espacio de cinco dias, en el ano 1981, en el marco de una expedicion organizada por el Servicio de Parques Nacionales y el Servicio de Patrullaje Maritimo del Ministerio de Seguridad Publica.
Geophysical Research …, 1990
We find that the local magnitude, M L , of the 18 October 1989 (UT) earthquake is 6.9, not 7.0 ‐ ... more We find that the local magnitude, M L , of the 18 October 1989 (UT) earthquake is 6.9, not 7.0 ‐ 7.1 as has tea reported. This value agrees with the moment magnitude, M w = 6.9, found by Kanamori and Satake (1990). ... Citation: McNally, KC, J. Yellin, M. Protti‐Quesada, G. ...
Revista Geografica De America Central, 1977
Geophys Res Lett, 2006
Arenal volcano is a small, active stratovolcano in Costa Rica. In 1998 and 2005, NASA's Lase... more Arenal volcano is a small, active stratovolcano in Costa Rica. In 1998 and 2005, NASA's Laser Vegetation Imaging Sensor (LVIS) was used to collect wide-swath 3-dimensional topographic images of the volcano. The LVIS is a full-waveform, scanning, medium-sized footprint, airborne laser altimeter system. By digitally recording the shape of the returning laser pulse (waveform), the LVIS provides a precise and accurate view of both the sub-canopy and canopy-top topographies as well as the vertical and horizontal structure of vegetation at 15-25 m horizontal resolution. By comparing georeferenced waveform data collected in 1998 and 2005, we mapped lava and pyroclastic flows deposited during this period. The active crater grew by 3.82 m yr-1. A flow volume estimate of 2.19 × 107 m3 (Dense Rock Equivalent of 1.89 × 107 m3 or 0.085 m3s-1) was obtained for the period 1998 to 2005. Precise elevation and elevation change data such as those provided by the LVIS are essential to calculate eruption volume and to study magma-supply dynamics, as well as assess the danger posed by the volcano to the local population from hazards such as pyroclastic flows.
Revista Geografica De America Central, 1983
Eos, Transactions American Geophysical Union, 2003
Arenal Volcano in Costa Rica has continuously erupted since 1968 exhibiting a variety of eruption... more Arenal Volcano in Costa Rica has continuously erupted since 1968 exhibiting a variety of eruption behaviors and evolving in a complex interplay between crystal fractionation, magma mixing, degassing, and wall-rock interaction (Reagan et al., 1987; Cigolini, 1998). We performed a pilot study of trace-element variations and U-series disequilibria in five whole rocks and, in three cases, mineral separates over the
Bulletin of Volcanology, 2002
The bulk composition of magma erupted from Volcán Arenal has remained nearly constant (SiO 2 = 53... more The bulk composition of magma erupted from Volcán Arenal has remained nearly constant (SiO 2 = 53.6-54.9 wt%; MgO = 5.0-4.5 wt%) during almost 30 years of continuous activity (1969-1996). None the less, clinopyroxene (cpx) phenocrysts and their spinel inclusions record a much more complex open-system evolution in which steady-state production of the erupted basaltic andesitic magma is linked to episodic injections of basalt into Arenal's magma conduit/reservoir system. High-resolution major element zoning profiles (electron microprobe) on a large number of phenocrysts (>14,000 analyses), tied to back-scattered electron (BSE) images, have been used to assess the compositional characteristics of the magmatic end members as well as the timing and dynamics of magma replenishment events. No two cpx phenocrysts have exactly the same zoning profile. The vast majority of our analyses record the crystallization of cpx (Cr 2 O 3 <0.12 wt%; Mg# = 65-79; Al/Ti = 2-7) from a liquid comparable to or more evolved than erupted magma compositions. However, half of all cpx grains are cored by high-Cr cpx (Cr 2 O 3 = 0.2-0.72 wt%) or contain similar basaltic compositions as abrupt growth bands in phenocrysts with and without high-Cr cores; phenocrysts with high-Cr cpx occur throughout the ongoing activity. In a few cases, high-Cr cpx occurs very near the outer margin of the grain without an apparent growth hiatus, particularly in 1968/69 and 1992/93. The main conclusions are: (1) all basaltic andesitic lavas erupted at Arenal during the ongoing activity that began in July, 1968, are the products of magma mixing, (2) clinopyroxenes record multiple replenishment events of basaltic magma in contrast to the near constancy of erupted bulk compositions, (3) some phenocrysts preserve records of multiple interactions with basaltic magmas requiring magmatic processes to operate on timescales shorter than residence times of some phenocrysts, (4) multiple occurrences of clinopyroxene with high-Cr rims suggest that basalt replenishment events have occurred with sub-decadal frequency and may predate eruption by months or less. From this we infer that Arenal volcano is underlain by a continuously active, smallvolume magmatic reservoir maintained in quasi-steady state by basalt recharge over several decades. The monotony of erupting Arenal magmas implies that fractionation, recharge, ascent, and eruption are well balanced in order for magmas to be essentially uniform while containing phenocrysts with vastly different growth histories at the time of eruption.
Revista Geográfica de Chile Terra Australis
The eruptive period between 1963-1965 at Irazú volcano showed that Costa Rica is highly vulnerabl... more The eruptive period between 1963-1965 at Irazú volcano showed that Costa Rica is highly vulnerable to ash fallout. Ash was carried by wind currents towards the Great Metropolitan Area (GMA), southwest to the summit, which contains about 60% of the national population. Previous work on hazard assessment for ash fall at Irazú only estimate influence areas without detailing hazard levels based on the observed distribution of events between 1963-1965. These cartographic models are not suited for realistic risk estimation, informed land use planning or proper emergency management. In this paper, we used the computer code NG-TEPHRA for simulating ash fallout from Irazú volcano, assessing the associated volcanic hazard and developing an improved hazard map from ash fall by devising a hazard index that combines the spatial probabilities of relevant scenarios with estimates of deposited ash volumes. Previous simulations result from our group were already calibrated against observed historical and field (geological) data from the 1963-1965 eruptive period and were used for obtaining the final hazard map. Our results represent a contribution for land use planning and emergency management purposes based on the application of computer models and interdisciplinary research towards numerically informed hazard models. RESUMEN Durante el periodo eruptivo entre 1963 y 1965, volcán Irazú mostró que Costa Rica es altamente vulnerable a la caída de ceniza. En esta ocasión la ceniza fue transportada por los vientos hacia la Gran Área Metropolitana (GAM), al suroeste del cráter, área que alberga al 60% de la población del país. Previos trabajos en la evaluación de la amenaza por caída de ceniza del Irazú solo estimaron el área de influencia basados en la distribución observada de los eventos entre 1963-1965 sin detallar la amenaza. Estos modelos cartográficos no son adecuados para una estimación realista del peligro, para el ordenamiento territorial o para la atención de emergencias. En este artículo, utilizamos el código de computadora NG-TEPHRA para simular la caída de ceniza del volcán Irazú, evaluando así el peligro volcánico asociado y desarrollando un mapa de amenaza mejorado de la caída de ceniza, mediante la elaboración de un índice de amenaza que combina las probabilidades espaciales de escenarios relevantes con estimaciones de volúmenes de ceniza depositados. Los resultados de simulaciones anteriores de nuestro grupo permitieron calibrar el modelo con los datos históricos y de campo observados (geológicos) del período eruptivo de 1963-1965 que se utilizaron para obtener el mapa de amenaza final. Nuestros resultados representan una contribución para el ordenamiento territorial y la atención de emergencias con base en la aplicación de modelos informáticos y la investigación interdisciplinaria hacia modelos de amenaza informados numéricamente.
Cuadernos de Geografía: Revista Colombiana de Geografía, 2015
The Poás volcano presents a series of hazards to the lives and activities of the communities in i... more The Poás volcano presents a series of hazards to the lives and activities of the communities in its surroundings; these hazards include ash fall, volcanic gases, ballistic projection, pyroclastic flows, lahars and lava flows. In the study described in this article, risks were zoned and integrated to form combined hazard maps for later use in territorial planning processes. With respect to methodology, the study was based on a heuristic approximation, which was supported with cartographic, geomorphological, and historical impact criteria to achieve a suitable product in terms of scale and ease of interpretation. These maps present greater detail and integration than other works and cartographies of volcanic hazards in Costa Rica.
Volcanic crater lakes are a major site of condensation for volatile elements and associated trace... more Volcanic crater lakes are a major site of condensation for volatile elements and associated trace elements produced by magmatic activity. Spherules of solid native sulfur up to several mm in diameter with sulfide inclusions (mainly corroded FeS) are common in the dense acidic waters of magmatically active lakes. They were most likely produced as hot gas (e.g. H2S or SO2)
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Papers by Eduardo Malavassi