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Transport and deposition processes of volcaniclastic deposits inferred by multivariate statistic analyses and GIS applications : The case of Nevado de Toluca volcano (Mexico)
No full textParticle size analysis is widely used in sedimentology to determine the characteristics of different depositional environments and infer flow transport and depositional processes. However for volcaniclastic flows, this methodology has been applied mainly for a descriptive purpose or for typical generic consideration of down flow variation of statistical parameters.
For this study we choose the case of Nevado de Toluca volcano (Mexico) due to the previous knowledge of its geological evolution, stratigraphic succession and spatial distribution of volcaniclastic units. Grain size analyses (by coupling photo-sieving, particle size and photosedimentographic analyses) and frequency distributions curves have been carried out to characterize block-and-ash flow and debris avalanche deposits.
The multivariate statistic analysis (discrimination function) shows that sedimentological parameters are good discriminators between samples belonging to block and ash flow and debris avalance deposit.
In addition, the application of the same methodology within each single deposit (DAD and BAF) allows to identify the presence of subpopulations and reveals differences among proximal, medial and distal facies. The resulting subpopulations have been plotted in a GIS environment to evidence these sedimentological variation respect to the deposit thickness and flow interaction with topography. By overlapping the flow thickness map with the subpopulation statistic analyses it is possible to define the relationships between facies and its position into the flow and to provide a model of transport and deposition mechanism of debris avalanche deposit and block and ash flow at Nevado de Toluca volcano
Structural arrangement of Mt. Etna Western Rift inferred from soil gas survey and geostatistical analysis
No full textSoil gas survey is a well known methodology to infer the presence of buried tectonic lineaments on volcano edifices from the evaluation of the orientation and extent of soil CO2 degassing anomalies. This application is an useful tool mainly where there is no evidence of tectonic structures found at the surface from geological survey, because of high resurfacing rate of investigated areas.
In this study attention was focused on an area located on Mt. Etna Western Rift, one of the most prominent, yet less understood and studied feeding systems of the volcano. It is constituted by many eruptive fissures and monogenetic cones emplaced from 15 ka until 1974.
In this area, a multidisciplinary approach was carried out based on detailed geological survey at 1:10,000 scale, soil CO2 efflux measurement, GIS and geostatistical applications, in order to better define the tectonic settings of this part of the volcano. The field work allowed identifying more than 15 emission centres as well as 10 eruptive fissures. The CO2 sampling strategy consisted of gas efflux measurements (with the accumulation chamber method) on a grid of sampling points about 100 m spaced. The geological and soil gas surveys allowed to obtain high resolution maps of the distribution of geological formations, structural lines and soil CO2 anomalies. A large amount of data were collected and were processed using a geostatistical approach.
Geostatistics combined with variogram analyses showed a good spatial correlation among CO2 anomalies, with an anisotropy mainly oriented N60°. The spatial pattern of these anomalies is in agreement with the structural arrangement of Mt. Etna Western Rift and suggests the presence of hidden faults sub-parallel to the main rift direction
Geological Map of the Western Rift of M. Etna (Italy)
No full textMt. Etna (3340 m a.s.l.) is the most active volcano in Europe, covering an area of 1250 km2, with more than 500 ka of geological history. In this work an accurate structural and geological field survey of the Western-Rift was performed at 1:10,000 scale, by using lithostratigraphic criteria and Unconformity-Bounded Units (UBU), in according to the guidelines suggested by International Subcommission on Stratigraphic Classification (ISSC) and the Italian Geological Survey (SGN). In order to improve the field-work data, an aerial photo interpretation was realized, by using high resolution ortho-photo and DEM elaboration, producing a mapping with high detail of the lava flows boundaries. During the field work activity the eruptive fissures configuration of the WR has been mapped, and lithostratigraphic units have been identified and organized in different ranks: formation, member and lava flow. The lithostratigraphic units allow to identify immediately during the field-survey the lithologic characteristics and stratigraphic relationships of rock bodies. To summarize and synthesise the main phases of the WR evolution, the lithostratigraphic units were grouped in different synthem units according to the stratigraphic framework of the volcano east flank, where the applied methodology has been defined and tested for the first time.
The volcanic succession of the West-Rift is formed by the oldest subaerial lava flows of Etna region (Adrano Synthem) that are unconformably covered by the lava flow succession generated by old volcano activity (La Timpe Synthem) and by products of Ellittico Volcano (Concazze Synthem). The main portion of the study area is formed by the product related to the Mongibello volcano eruptive activity of the past 14 ka (Il Piano Synthem). The Mongibello lava succession is constituted by the superimposition of several lava flow fields generated by more than 50 eruptive fissures, forming the core of the West-Rift.
The eruptive fissures strike about 260°, fed several monogenetic cones and are concentrated in a bounded zone 4 km-wide, located in the central portion of the western flank. Some of these eruptive fissures took place in the last 2 ka and are reported in historical chronicles.
The result of this work is a detailed geological map at 1:20,000 scale of the WR, which points out the geological and structural setting of the area and significantly improve the knowledge of its evolution in order to better assess the whole eruptive history of Mt. Etna as well as its structural framework
Tectonic evolution of the central-eastern sector of Trans Mexican volcanic belt and its influence on the eruptive history of the Nevado de Toluca Volcano (Mexico)
No full textThe Nevado de Toluca is an andesitic to dacitic stratovolcano of Late Pliocene–Holocene age located within the central and eastern sectors of the Trans Mexican Volcanic Belt. Morphostructural analysis, aerial photograph and satellite image interpretation, structural analysis and geological fieldwork were methods used to investigate the relationship between the evolution of the volcano and the tectonic
framework of its basement. The study revealed that the area of Nevado de Toluca is affected by three main fault systems that intersect
close to the volcanic edifice. These are from oldest to youngest, the Taxco–Querétaro, San Antonio and Tenango fault systems. The NNW–SSE Taxco–Querétaro fault system was active in the area since Early Miocene, and is characterized by right-lateral transtensive movement. Its reactivation during Early toMiddle Pleistocene was responsible for the emplacement of andesitic to dacitic lava flows and domes of La Cieneguilla Supersynthem. The NE–SW San Antonio fault systemwas active during Late Pliocene, before the reactivation of the Taxco–Querétaro fault system, and is characterized by extensional left-lateral oblique-slip kinematics. The youngest is the E–W
Tenango fault system that has been active since Late Pleistocene. This fault systemis characterized by transtensive left-lateral strike-slip movement, and partly coeval with the youngest eruptive phase, the Nevado Supersynthem, which formed the present summit cone of the Nevado de Toluca volcano. The stress re-orientation from the Taxco–Querétaro to the Tenango fault system during Late Pleistocene is responsible for the ∼ 1 Ma hiatus in the magmatic activity between 1.15 Ma and 42 ka. After this period of repose, the eruptive style drastically changed from effusive to explosive with the emission of dacitic products. The methodology presented here furnish new data
that can be used to better assess the complex structural evolution of this sector of the Trans Mexican Volcanic Belt and to understand the
influence of changes in the tectonic setting on the growth of volcanic edifices
Pregnancy in patients with mechanical prosthetic heart valves. Our experience regarding 98 pregnancies in 57 patients
No full textNinety-eight pregnancies in 57 patients with mechanical (ball or tilting disc) prosthetic heart valves are described. Sixty-one pregnancies developed in 36 patients with a mitral prosthesis, 12 pregnancies in 9 patients with an aortic prosthesis, 17 pregnancies in 10 patients with both mitral and aortic prostheses and 8 pregnancies in 2 patients with mitral and tricuspid prostheses. All patients were in I or in II NYHA class at conception and no significative change was noted during pregnancy. All the patients were treated with oral anticoagulant therapy at conception. Different kinds of antithrombotic and antiembolic prophylaxis were employed. There were 13 voluntary interruptions of pregnancy and 37 spontaneous abortions. In the 47 newborn 2 malformation complications (1 warfarin syndrome, 1 cleft palate) and 4 haemorrhagic complications (without sequelae) were noted. Two fatal thromboses of a mitral prosthesis occurred; systemic embolic complications were noted in 7 cases. These observations suggested different incidences of complications regarding the antithrombotic and anti-embolic prophylaxis. The authors point out the high risk of thrombotic and embolic complications and the low rate of successful outcome of pregnancy in these patients
Map of deformation partitioning in the polydeformed and polymetamorphic Austroalpine basement in Valtellina and Val Camonica, (Central Alps)
No full textFoliation trajectories, superposed to classical lithological information, have been used in this essay to represent the tectonometamorphic evolution of metamorphic rocks at the map scale. Each trajectory is characterized by a chronological connotation (dot pattern) and by a metamorphic connotation (colour); the relative timing of tectonic imprints has been reconstructed by means of the superposition of structures, while the metamorphic terms have been attributed on the basis of a meso- and microstructural-petrographic analysis of the metamorphic assemblages supporting all fabric elements (e.g. foliations, lineations). In addition, fabric gradients have been reported where pre-existing, quasi-isotropic rocks could be utilised (e.g. igneous rocks); these have been represented as colour gradients: from light colours (low strain domains = coronitic fabrics) to full colours (high strain domains = mylonitic fabrics). This new mapping approach, applied to a section of the Austroalpine domain of the Central Alps (Passo Mortirolo, Alta Val Camonica - Valtellina, Italy), which is characterized by polyphasic pre-Alpine and Alpine tectonometamorphic cycles, made the complete representation of lithostratigraphic and tectonometamorphic evolutions possible; therefore, this map is an example of a new method of representation of the full tectono-metamorphic history of a continental crust that underwent two superposed tectonic cycles (Variscan andAlpine) and successive structural stages related to a sequence of metamorphic re-equilibrations. Besides, this approach can be successfully applied in all tectonic and metamorphic settings generally recorded by metamorphic basements
A Geographical Information System for Volcanic Hazard Modelling
No full textHazard maps are fundamental for the development of land and resource management
plans. In this paper we focus on volcanic hazards. In particular we discuss a possible
approach to the construction of the lava flow hazard map for the Mount Etna, which is the
most active volcano in Europe. The core of our proposal is a lava flow simulation
system. We present the main characteristics of the underlying simulation model and how
it has been validated. Next we introduce a novel and still in progress approach to the
clustering of lava flow emission points based on data mining techniques
Maps of foliation trajectories and metamorphic imprints: a tool to individuate tectono-metamorphic units in the Southalpine metamorphic basement.
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