Seismic quantification of the explosions that destroyed the dome of Volcán de Colima, Mexico, in July–August 2003     

Vyacheslav M. Zobin  Carlos J. Navarro-Ochoa  Gabriel A. Reyes-Dávila 《Bulletin of Volcanology》2006,69(2):141-147

In July–August 2003, the andesitic lava dome at Volcán de Colima, México, was destroyed by a sequence of explosions that replaced the 2×10⁶ m³ dome with a crater 200 m across and 30 m deep. The two strongest explosions occurred on July 17 and August 28. The initial low-frequency impulses that they produced, which were recorded on broadband seismic records, allowed an estimation of the counter forces of the initiating process as being equal to 0.3×10¹¹ N and 1×10¹¹ N for the July and August events, respectively. The seismic characteristics follow the Nishimura-Hamaguchi scaling law for volcanic explosions, reflecting self-similarity in the processes initiating explosive events. The results also show that counter forces can discriminate between the sizes of explosive eruptions that are assigned the same magnitude by conventional methods of classification such as the Volcanic Explosivity Index. The increasing use of broadband seismometers may therefore provide the basis for using counter forces to determine the magnitude of explosive eruptions.  相似文献   

Pahoehoe flows from the central Paraná Continental Flood Basalts     

Breno L. Waichel  Evandro F. de Lima  Romulo Lubachesky  Carlos A. Sommer 《Bulletin of Volcanology》2006,68(7-8):599-610

Inflated and compound pahoehoe flows have been identified within the central Paraná Continental Flood Basalts based upon their morphology, surface features, and internal zonation. Pahoehoe flow features have been studied at five localities in the western portion of Paraná State, Brazil: Ponte Queimada, Toledo, Rio Quitéria, Matelandia and Cascavel. We have interpreted the newly recognized flow features using concepts of Hawaiian pahoehoe formation and emplacement that have been previously applied to the Columbia River Basalt and Deccan Plateau. Surface features and/or internal structure typical from pahoehoe lavas are observed in all studied areas and features like inflation clefts, squeeze-ups, breakouts, and P-type lobes with two levels of pipe vesicles are indicative of inflation in these flows. The thinner, compound pahoehoe flows are predominantly composed of P-type lobes and probably emerged at the end of large inflated flows on shallow slopes. The presence of vesicular cores in the majority of compound lobes and the common occurrence of segregation structures suggests high water content in the pahoehoe lavas from the central PCFB. More volcanological studies are necessary to determinate the rheology of lavas and refine emplacement models.Editorial responsibility: C. Kilburn  相似文献   

Comments on: ‘The Neutral, Barotropic Planetary Boundary Layer, Capped by a Low-Level Inversion’ by G. D. Hess, Boundary-Layer Meteorology (2004) 110, pp. 319–355     

Juan Carlos Bergmann 《Boundary-Layer Meteorology》2006,119(1):171-179

Precision measurements indicate that the stability capping of the neutral planetary boundary layer (PBL) that leads to a reduced PBL height is caused by the very stable upper part of the PBL, rather than by an overlying inversion. Radiative processes related to liquid water in boundary-layer clouds seem to play the key role for the formation of the stable upper PBL. The famous Leipzig Profile – generally considered as an example of a neutral PBL – has been included in Hess’s analysis because its PBL height is considerably lower than the ca. 3000 m to be expected by numerical models in truly neutral conditions. An analysis of the original observations reveals that the Leipzig PBL was stable and that it can be consistently treated as a ‘normal’ stable PBL with a height of ca. 700 m. A further finding is that the super-geostrophic PBL wind speed maxima predicted by almost all models are not observed in near-steady-state conditions. For the ‘ranking’ of analytical models versus numerical models, the comparisons with measurements show that the analytical models perform comparably well and even partially better than the numerical models.  相似文献   

Coupled thermal, hydraulic and geochemical evolution of pyritic tailings in unsaturated column experiments     

Patricia Acero  Carlos Ayora  Jesús Carrera 《Geochimica et cosmochimica acta》2007,71(22):5325-5338

The evolution of pore-water and the composition of solid phases in the vadose zone of pyritic tailings was studied by means of unsaturated column experiments. Several columns of water-saturated mine tailings were dried during 125 days under controlled laboratory conditions. The columns were dismantled at four successive drying stages and the evolution of pore-water, mineralogy, water content and temperature was characterized.Sulfide and aluminosilicate minerals present in the waste dissolved, releasing sulfate and other solutes (mainly Fe, Zn, Cu, Al, Mg and Ca) to the pore-water. Evaporation caused a crust of efflorescent, water-soluble sulfates to develop over the complete top surface of the columns and into the pores of the underlying waste material. This crust, which has also been identified in the field, changed the hydraulic properties of the tailings and produced a decrease in the evaporation rate of the columns. Moreover, these water-soluble precipitates (mainly rozenite, szomolnokite, halotrichite, hexahydrite, mirabilite and gypsum) acted as temporary sinks for Cd, Pb, Co and Ni, which could be released to the surface run-off or the groundwaters during rainfall events under field conditions.Pore-water evolution was determined not only by geochemical processes (dissolution of sulfides and aluminosilicates, precipitation of secondary phases) but also by thermal and hydraulic processes. Progressive dilution was observed in the lower part of the columns. Dilution was caused by the thermally driven vapor flux from the top of the column to its colder bottom and subsequent condensation therein. This process, which may also occur in tailings under sub-arid climate, played a key role on the evolution of pore-water with increasing drying.  相似文献   

Deconstructing the best case scenario: lessons from water politics in La Paz-El Alto, Bolivia     

Nina Laurie  Carlos Crespo 《Geoforum》2007,38(5):841-854

For nearly a decade the La Paz-El Alto concession in Bolivia was heralded by donor organizations, the state and the commercial water industry alike as an emblematic ‘pro-poor’ water concession under the private sector model. Managed by one of the largest water multinationals in the world (the French company Suez), the network was extended beyond the new connections required by the original ‘pro-poor’ contract, acclaimed as a pioneer of new pro-poor technologies and frequently disseminated internationally as an example of best practice. This paper analyses the La Paz-El Alto concession’s pro-poor image focusing on issues of social exclusion and network extension, contract negotiation, participation and transparency. It documents the rise of social protest about the concession and critiques the failure of neoliberal regulatory systems to promote accountability to the poor. In the context of the continued transnationalisation of the water industry the paper highlights the need for new mechanisms and delivery models to ensure greater national control over private companies and the development of a framework for international water governance.  相似文献   

Homogeneity of the Geochemical Reference Material BRP-1 (Paraná Basin Basalt) and Assessment of Minimum Mass     

Aloísio J.B. Cotta  Jacinta Enzweiler  Stephen A. Wilson  Carlos A. Pérez  Antonio J.R. Nardy  João H. Larizzatti 《Geostandards and Geoanalytical Research》2007,31(4):379-393

Reference materials (RM) are required for quantitative analyses and their successful use is associated with the degree of homogeneity, and the traceability and confidence limits of the values established by characterisation. During the production of a RM, the chemical characterisation can only commence after it has been demonstrated that the material has the required level of homogeneity. Here we describe the preparation of BRP-1, a proposed geochemical reference material, and the results of the tests to evaluate its degree of homogeneity between and within bottles. BRP-1 is the first of two geochemical RM being produced by Brazilian institutions in collaboration with the United States Geological Survey (USGS) and the International Association of Geoanalysts (IAG). Two test portions of twenty bottles of BRP-1 were analysed by wavelength dispersive-XRF spectrometry and major, minor and eighteen trace elements were determined. The results show that for most of the investigated elements, the units of BRP-1 were homogeneous at conditions approximately three times more rigorous than those strived for by the test of "sufficient homogeneity". Furthermore, the within bottle homogeneity of BRP-1 was evaluated using small beam (1 mm²) synchrotron radiation XRF spectrometry and, for comparison, the USGS reference materials BCR-2 and GSP-2 were also evaluated. From our data, it has been possible to assign representative minimum masses for some major constituents (1 mg) and for some trace elements (1-13 mg), except Zr in GSP-2, for which test portions of 74 mg are recommended.  相似文献   

Structural framework and Mesozoic–Cenozoic evolution of Ponta Grossa Arch, Paraná Basin, southern Brazil     

Michael Strugale  Sidnei Pires Rostirolla  Fernando Mancini  Carlos Vieira Portela Filho  Francisco Jos Fonseca Ferreira  Rafael Corrêa de Freitas 《Journal of South American Earth Sciences》2007,24(2-4):203-227

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Mock 2dF and SDSS galaxy redshift surveys   总被引：1，自引：0，他引：1  

Shaun Cole  Steve Hatton  David H. Weinberg  & Carlos S. Frenk 《Monthly notices of the Royal Astronomical Society》1998,300(4):945-966

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Are the Venezuelan fault systems part of the southern Caribbean plate boundary?     

Carlos Schubert 《International Journal of Earth Sciences》1981,70(2):542-551

Three major fault systems have been recognized in Venezuela: the Oca, Boconó, and El Pilar fault zones. The Boconó-El Pilar system is an active, Late Pleistocene-Holocene fault system, which extends for over 1300 km between the Venezuela-Colombia border, through the Venezuelan Andes and along the northern Venezuelan coast, to the east of Trinidad. Recent tectonic evidence suggests that until the Late Tertiary or Early Quaternary, the Caribbean Plate-South America Plate boundary included the El Pilar and Oca fault systems. Since then, it has included the Boconó fault system. Right-lateral offset along these fault systems is not sufficient to derive the Caribbean Plate from Pacific crust; alternatively, the Caribbean Plate may have been a part of the South America Plate until comparatively recent geologic-time.

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Zusammenfassung Drei wichtige Bruchsysteme sind in Venezuela festgestellt worden: die Oca, Boconé und El Pilar Bruchzonen. Das Boconó-El-Pilar-System ist ein aktives, Spätpleistozänes-Holozänes System, daß sich über mehr als 1300 km erstreckt, von der venezolanischkolumbianischen Grenze, durch die venezolanischen Anden und längs der nördlichen venezolanischen Küste, bis östlich von Trinidad. Rezente tektonische Daten lassen andeuten, daß bis zum Spättertiär oder Frühquartär, die Grenze zwischen der Karibischen Platte und der Südamerika-Platte die El Pilar- und Oca-Bruchsysteme einschloß. Später hat sie das Boconó-Bruchsystem eingeschlossen. Rechtsinnige Blattverschiebung an diesen Bruchsystemen ist nicht groß genug, um die Karibische Platte als ein Stück pazifischer Kruste zu betrachten; oder aber, die Karibische Platte war mit der Südamerika-Platte vereinigt bis zu einem relativ jungen geologischen Alter.

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Resumen Se han establecido tres sistemas mayores de fallamiento en Venezuela: las zonas de falla de Oca, Boconó y El Pilar. El sistema de Boconó-El Pilar es un sistema de falla activo pleistoceno-holoceno, el cual se extiende por más de 1300 km entre la frontera colombo-venezolana, a traves de los Andes venezolanos y a lo largo de la costa norte de Venezuela, hasta más al este de Trinidad. Evidencias tectónicas recientes sugieren que hasta el Terciario Tardio o Cuatemario Temprano, el límite entre las Plaças del Caribe y de América del Sur incluía los sistemas de falla de Oca y El Pilar. Desde entonces incluye al sistema de falla de Boconó. El desplazamiento de rumbo hacia la derecha a lo largo de estos sistemas de fallamiento no es suficiente para derivar la Plaça del Caribe de la corteza pacifica; alternativamente, la Placa del Caribe puede haber sido parte de la Placa de América del Sur hasta una época geológica relativamente reciente.

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Dedicated to the memory of John D. Weaver.  相似文献   

Late Pleistocene glaciation of Páramo de La Culata,north-central Venezuelan Andes     

Dr. Carlos Schubert  Mr. Sam Valastro 《International Journal of Earth Sciences》1974,63(2):516-538

Late Pleistocene glacial features in the Páramo de La Culata region, north-central Venezuelan Andes, include: 1. depositional features: morainic till and fluvio-glacial deposits (terrace gravels); 2. sculptured features: glaciated valleys, cirques, horns, and arêtes; and 3. erosional features: striation and grooving, polished rock, roches moutonnées and whaleback forms, and erratic boulders. Two main levels of moraines were found, an older one at 2600 m elevation, and a younger one between 3000 and 3500 m. The difference in age is reflected by the higher degree of weathering, erosion, and vegetation cover of the lower level, as compared with the higher level. Radiocarbon dating, and a comparison and correlation of these glacial features with those of adjacent regions, indicates that the lower morainic level (2600 m) is probably the result of the main glacial advance of the Late Wisconsin Glaciation. The main morainic level (3000 to 3500 m) was probably formed by the latest Wisconsin glacial advance. The Late Pleistocene snow-line depression reached approximately 1200 m below the present snow-line (i. e., down to approximately 3500 m).  相似文献