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This paper presents the analysis of a regional groundwater model via Feflow in tropical regions using two techniques: pilot points (PP) and constant zones (CZ). These methodologies allow the proper identification of biased parameters and heterogeneities of hydraulic properties. For this purpose, we developed a numerical density-variable model that is limited to reinterpreted data from real measurements. For the CZ, the initial parameters are considered constant; in contrast, in the PP technique, the initial parameters are assigned according to interpolations using in-situ point measurements. The developed model was applied in an area under the influence of the Inter-tropical Convergence Zone, located in the middle valley of Magdalena (MMV). This area is important in the development of Colombia due to its contribution to Gross Domestic Product, and it has been subject to significant changes in land use, as a result of intense economic activities. The established model shows a link between the observed state variable (hydraulic head) and hydraulic conductivity (K) proving the importance of spatial heterogeneity in K. The model is calibrated in order to establish K, the porosity and the specific storage capacity, reducing the mean square error of the state variable dependable on the observation points. The results show that the PP system approach provides a better heterogeneity representation and shows that each parameter is sensitive, and does not depend on other parameters. This research compiles the first breakthrough toward a methodology to assertively restrict a highly parameterized inverse regional model in a tropical basin. [ABSTRACT FROM AUTHOR]

Fine-grained and mainly reddish color, compact and slightly breccious and vesicular pyrometamorphic rocks (natural clinker) are associated to the spontaneous combustion of coal seams of the Cerrejón Formation exploited by Carbones del Cerrejón Limited in La Guajira Peninsula (Caribbean Region of Colombia). These rocks constitute remaining inorganic materials derived from claystones, mudstones and sandstones originally associated with the coal and are essentially a complex mixture of various amorphous and crystalline inorganic constituents. In this paper, a petrographic characterization of natural clinker, as well as the application of the X-ray diffraction (Rietveld method) by mean of quantitative analysis of its mineral phases were carried out. The RIQAS program was used for the refinement of X ray powder diffraction profiles, analyzing the importance of using the correct isostructural models for each of the existing phases, which were obtained from the Inorganic Crystal Structure Database (ICSD). The results obtained in this investigation show that the Rietveld method can be used as a powerful tool in the quantitative analysis of phases in polycrystalline samples, which has been a traditional problem in geology. [ABSTRACT FROM AUTHOR]

Metamorphic pressure and temperature trajectories are generally used as tools to interpret the tectonic history of deformed belts of rocks that record past activity along active plate margins. The pre-Devonian metamorphic sequence of the Silgará Formation forms part of the ancient basement of the central Santander Massif, including pelitic schists, siliceous schists and intercalation of amphibolites accompanied by marble. This metasedimentary unit has been affected by Barrovian type metamorphism under middle-pressure/high-temperature conditions. This paper presents on the relationship of tectonic processes to pressure-temperature paths development. Detailed petrologic analysis of pelites and related rocks has been used to constrain the P-T history of this region in the eastern colombian cordillera. Mineral assemblages and Geothermobarometric calculations indicate metamorphic temperatures and pressures of 400-600 °C and 4.0-6.5 kbar, respectively. [ABSTRACT FROM AUTHOR]

Metacarbonate rocks (pure and impure marbles, carbonate-silicate rocks, calc-silicate rocks and carbonate-bearing silicate rocks) form a very complex group within the metamorphic sequence of the Silgará Formation at the central Santander Massif(CSM). These rocks are interpreted as derived from a sedimentary sequence (including limestones and dolostones, carbonate-bearing mudstones, sandstones, tuffaceous and evaporitic sediments and marlstones) overprinted by near-isochemical regional metamorphism. They usually appear as scarce intercalations from millimeter up to meter scale, within the high-grade pelitic rocks, in the lower part of the metamorphic section, although the proportion of metacarbonate rocks can be higher and different marble layers are exploited. We report for the first time the occurrence of a "reaction calcic exoskarn", which corresponds to such metacarbonate rocks, taking into account that a skarn can be developed during regional metamorphism and by different metasomatic processes, adjacent to intrusive bodies, along faults and shear zones, and what defines these rocks as a skarn is its mineralogy, which includes a variety of calc-silicate and associated minerals, usually dominated by garnet and pyroxene. Therefore, this paper focus attention to the occurrence of metacarbonate and related rocks, which occurs as small scale reactions zones that show a gradational contact from garnet-bearing pelitic rocks to marbles or carbonate-silicate rocks, giving particular interest to the calc-silicate rocks, which are characterized by the presence of elongated grains of banded clinopyroxene (diopside) and scapolite and massive or scattered garnet. Several reaction-zones occur in the contact between impure calcite marble and garnet-bearing metapelite and the sequence of mineral assemblages in these reaction zones is: biotite + plagioclase ± K-feldspar ± garnet (Zone I), biotite + plagioclase ± K-feldspar ± garnet ± staurolite ± epidote (Zone II), plagioclase + amphibole ± garnet + epidote (Zone III), amphibole + diopside + garnet + plagioclase (Zone IV), plagioclase + diopside ± scapolite (Zone V). epidote ± calcite (Zone VI), and calcite ± dolomite (Zone VII). [ABSTRACT FROM AUTHOR]

The National Institute of Geology and Mining, INGEOMINAS -- Colombia, and the Federal Institute for Geosciences and Natural Resources, BGR -- Germany, perform since 1997 as a joint venture multi-parameter measurements at the Galeras volcano, in the southwest of Colombia. Since the end of 1998 the Multi-parameter Station at Galeras (Estación Multiparámetro del Galeras -- EMG) includes the continuous monitoring of electromagnetic variations. The electromagnetic (EM) station is located at the north-eastern foot walls of the central cone inside the caldera. During almost six years of electromagnetic monitoring, the data did not show significant variations of the electromagnetic field, which could be related to the volcanic activity. In July 2004 a new active period of Galeras began with two strong ash emissions. During both emissions strong self potential-(SP) signals were recorded lasting for several hours. The present paper will present the data which could give some indications on the movements of liquids during ash emissions. [ABSTRACT FROM AUTHOR]

Automatic classification of seismic signals has been typically carried out on feature-based representations. Recent research works have shown that constructing classifiers on dissimilarity representations is a more practical and, sometimes, a more accurate solution for some pattern recognition problems. In this paper, we consider Bayesian classifiers constructed on dissimilarity representations. We show that such classifiers are a feasible and reliable alternative for automatic classification of seismic signals. Our experiments were conducted on a dataset containing seismic signals recorded by two selected stations of the monitoring network at Nevado del Ruiz Volcano. Dissimilarity representations were constructed by calculating pairwise Euclidean distances and a non-Euclidean measure on the normalized spectra, which is based on the difference in area between spectral curves. Results show that even though Euclidean dissimilarities have advantageous properties, non-Euclidean measures can be beneficial for matching spectra of seismic signals. [ABSTRACT FROM AUTHOR]

This paper presents the results provided by the fine-scale thermohaline structure of near-surface layer (NSL) study done in the Colombian Pacific Ocean (CPO). Mathematical models for different regimes of the near-surface layer are formulated. Based on three stations, an hourly analysis of meteorological data, thickness change, temperature and salinity of this layer was done. The principles of formation of the thermohaline structure for NSL over CPO are related to night convection, wind-wave mixing, volume absorption of radiant energy and precipitation. [ABSTRACT FROM AUTHOR]