Petrology of pumices of April 1993 eruption of Lascar (Atacama, Chile)     

Bernard Déruelle  Oscar Figueroa A.  Eduardo Medina T.  Jose Viramonte G.  Mario Maragaño C. 《地学学报》1996,8(2):191-199

Lascar Volcano (Atacama, Chile) erupted on 18–20 April 1993. Several sub-Plinian explosions occurred, and some were mushroom-shaped. The highest column rose up to 23 km. Ash clouds crossed South America eastwards. Dacite pumice falls made of blocks and ashes were deposited on the flanks of the volcano as a result of collapsed columns. The pumice contains phenocrysts of plagioclase, enstatite, augite, biotite, magnetite and ilmenite and small crystals of apatite. The 1992 previous andesite dome inside the crater was destroyed. Banded blocks resulting from mingling of the dacitic pumice and andesite from the dome are found in the pumice flow. Both the lava dome and the pumice are representative of the Lascar high-K magma unit. Dacitic pumice is a product of crystal fractionation of the andesitic magma.  相似文献   

Preface     

Elisabete M. de Gouveia Dal Pino  Anthony L. Peratt  Gustavo A. Medina Tanco  Abraham C. -L. Chian 《Astrophysics and Space Science》1996,242(1-2):1-2

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Use of three widely spread plant species from American arid regions for exploration of tin mineralizations     

J. L. Fernandez-Turiel  P. Aceolaza  M. E. Medina  J. Saavedra  F. Durand 《Journal of Arid Environments》2003,53(4):607-618

The ability to accumulate trace element contents of three plant species of widespread occurrence in the semi-arid regions of middle and southern South America (Larrea cuneifolia Cav., Cercidium praecox (Ruiz & Pav.) Harms, and Bulnesia retama (Gillies ex Hook. & Arn.) Griseb.) has been considered in order to determine their application to the exploration of tin mineralizations. Two of the three studied species can be considered as suitable for biogeochemical exploration (L. cuneifolia and C. praecox). Concentrations of As, Cd, and Mo reflect the known tin mineralization. L. cuneifolia and B. retama showed the highest and lowest trace element accumulation rates. Only zinc is preferentially accumulated in C. praecox. In addition, L. cuneifolia and C. praecox could be of environmental interest in As-bearing areas due to the accumulation capability for such element.  相似文献   

Beach morphodynamics forcements in oiled shorelines: Coupled physical and chemical processes during and after fuel burial     

Bernabeu AM  Nuez de la Fuente M  Rey D  Rubio B  Vilas F  Medina R  González ME 《Marine pollution bulletin》2006,52(10):1156-1168

In November 2002, the sinking of the Prestige oil tanker off the Galician coast (N.W. Spain) caused the largest ecological catastrophe in the history of Spain, affecting the coast called the 'Costa da Morte' (Galicia, N.W. Spain). This work is focused on the study of the oil contamination of the intertidal area of two beaches located on this stretch of coast. The study of twenty cores extracted from both beaches has identified fuel embedded in the sedimentary column up to a depth of 2.38 m (this being the maximum depth of extraction). This, along with the presence of oil below the groundwater indicates the existence of a new factor which determines the burial of oil: the morphodynamic behaviour of the beach. Furthermore, this morphodynamic variation conditions the physical appearance of the buried oil. Four different types have been identified: tar-balls (cm), particles (mm), oil coatings on sediment grains and on emulsion, with distribution patterns conditioned by the degree of wave exposure. The analysis of the information obtained have permitted the development of a conceptual model of the burial and oil evolution in the sedimentary column in relation to wave exposure, and thus to the morphodynamic variability of the beach.  相似文献   

Analysis of clustering and selection algorithms for the study of multivariate wave climate     

Paula Camus  Fernando J. Mendez  Raul Medina  Antonio S. Cofiño 《Coastal Engineering》2011

Recent wave reanalysis databases require the application of techniques capable of managing huge amounts of information. In this paper, several clustering and selection algorithms: K-Means (KMA), self-organizing maps (SOM) and Maximum Dissimilarity (MDA) have been applied to analyze trivariate hourly time series of met-ocean parameters (significant wave height, mean period, and mean wave direction). A methodology has been developed to apply the aforementioned techniques to wave climate analysis, which implies data pre-processing and slight modifications in the algorithms. Results show that: a) the SOM classifies the wave climate in the relevant “wave types” projected in a bidimensional lattice, providing an easy visualization and probabilistic multidimensional analysis; b) the KMA technique correctly represents the average wave climate and can be used in several coastal applications such as longshore drift or harbor agitation; c) the MDA algorithm allows selecting a representative subset of the wave climate diversity quite suitable to be implemented in a nearshore propagation methodology.  相似文献   

Incorporating Auxiliary Geophysical Data into Ground-Water Flow Parameter Estimation   总被引：1，自引：0，他引：1  

Giorgio Cassiani  Miguel A. Medina  Jr. 《Ground water》1997,35(1):79-91

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Gravity and seismicity analyses of the El Chichon volcano,Chiapas, Mexico     

F. Medina  T. Gonzalez-Moran  L. Gonzalez 《Pure and Applied Geophysics》1990,133(1):149-165

Subduction induced compressional stress, lateral displacement faults probably linked to the NW extension of the Polochic-Motagua fault system, and local magma emplacement create a complex geological setting for the El Chichon volcano.Gravity analysis reveals that the principal structures in the area correspond to synclines and anticlines. Downward continuation of the gravity field suggests the presence of magma emplacement SE of the volcano. This magmatic emplacement appears to be the principal cause of the truncation of the syncline in which the volcano lies.Analyses of earthquakes occurring after eruptions show that the vertical distribution of events is confined to a roughly cylindrical zone which correlates well with the region of magmatic emplacement inferred from the gravity analysis.Even though more than 350 km separate the volcano from the Middle American trench, the compressional stress regime reported for the area may correlate with subduction stress (N30°E). However, the strike direction for the principal faults in the zone, N60°W, permits us to postulate that the NW extension of the Polochic-Motagua fault system is implicated in the local tectonics of the El Chichon area.  相似文献   

Spatial variability of soil nutrients in disturbed riverine mangrove forests at different stages of regeneration in the San Juan River estuary,Venezuela     

Victor?H.?Rivera-MonroyEmail author  Robert?R.?Twilley  Ernesto?Medina  E.?Barry?Moser  Leonor?Botero  Ana?Marta?Francisco  Evelyn?Bullard 《Estuaries and Coasts》2004,27(1):44-57

Geostatistical analysis of selected soil properties were performed in two mangrove sites (B7 and B9) dominated by the mangrove speciesRhizophora mangle along the San Juan River, Venezuela, to evaluate the effect of forest disturbance on nutrient spatial distributions. Plots within area B7 were clear-cut in 1972–1973 and in area B9 in 1982–1983. Four plots within each area were systematically selected and represented natural (2) and regenerated (2) forests. Individual plots were 1.5 ha in B7 and 1.25 ha in B9 and sampled at a resolution of 25 m. Soil samples were obtained at the intersection of an aligned grid with 90 points in B7 and 78 points in B9. Measured soil properties included salinity, total nitrogen, total carbon, total phosphorus, osmolality, and pore water cation concentrations (potassium, calcium, magnesium, and sodium). Sites were sampled in May 1996 and 1997, although spatial analysis was performed only for the data obtained in May 1997. Geostatistical analysis showed that most of the variables tested were spatially auto-correlated within each area and that there were no differences between regenerated and natural plots. Structural variance as a proportion of sample variance ranged from 55–99% for most of the properties. The significant spatial dependence observed for most of the variables in natural and regenerated plots, despite management schedules, indicates that clear-cutting did not have an effect on modifying the distribution of nutrient concentrations. These results suggest that after 15 and 25 yr following forest disturbance nutrient distributions were reestablished either there was not a net effect on patterns of element loss or tidal input was stronger than plant modifications of soils.  相似文献   

Historic and holocene volcanic centers in NW Mexico
A supplement to the IAVCEI catalogue     

F. Medina  F. Suarez  J. M. Espindola 《Bulletin of Volcanology》1989,51(Z1):91-93

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The Rabat and Larache boulder fields; new examples of high-energy deposits related to storms and tsunami waves in north-western Morocco     

F. Medina  N. Mhammdi  A. Chiguer  M. Akil  E. B. Jaaidi 《Natural Hazards》2011,59(2):725-747

The coastal areas of south-west Iberia and north-west Morocco host numerous megaclast accumulations thought to have been emplaced by high-energy waves, namely by the major tsunami related to the 1 November 1755 AD earthquake. New observations were carried out along several transects from Rabat and Larache areas, using statistical methods applied to boulder size. The main results are (a) the boulders belong to two or three sources located within the Pleistocene–Holocene formations of both areas, but only from a single source at Harhoura; (b) the boulders in Larache are generally small, thin and show a normal polarity, whereas those of Rabat are much larger and are often overturned; (c) the directions of inclination of imbricate boulders are variable at Rabat (N, NW and W), whereas they are constant in Larache (WNW); (d) the blocks were displaced for distances up to 150 m in Rabat, while the displacement of the Larache boulders was stopped by the MHW cliff; (e) the hydrodynamic equations suggest that tsunami waves, with maximum amplitudes of 5–11 m in Rabat and 4.5 m in Larache, were responsible for the displacement of the largest boulders, whereas storms may have displaced smaller ones.  相似文献