![]() Even with very large images and a computer with little memory, the visualization tools remain powerful thanks to tiling and deferred execution. This thesis presents a new method to separate connected grains, which is more efficient than traditional methods on long particles and on those containing holes. In order to optimize memory management during certain operations, we adapted the algorithm of region growing so that it is compatible with tiling and deferred execution. Other innovating tools, such as granulometric analysis and computerized point counting, were developed. The latter represents an alternative when the various segmentation methods do not allow a satisfying estimate of the modal composition. It offers several advantages compared to the counting under the microscope, like the restriction to a region type (after segmentation) in order to quickly estimate its subclasses. In JMicroVision, characteristics of the objects extracted from the image can be highlighted in a visual way either by various diagrams or by a coloring of objects according to their value (in relation with a selected descriptor). The rendering of the project or a portion of it can be exported in several image formats or as vector graphics in the SVG format. All data is also exportable in the CSV format. JMicroVision contains tools having various degrees of automation in order to handle with complex and varied images. The operator's intuition is nevertheless crucial for deciding which is the right way to proceed and for adjusting the parameters in the user's interface. For example, in order to characterize porosity, a supervised classification of the pore types was carried out with a new parameter named “context”, which describes the neighborhood to the pores.ĭuring an eruption, the level of threat a volcano poses to its surroundings is related Several procedures for petrographic analyses are proposed in the second part of this thesis. An effusive eruption generating slow-moving lavaįlows will be a lot less destructive than a violent explosive eruption producing large pyroclastic density currents (PDC). In this thesis, I investigate the role of pre-eruptive storage conditions, volatileĬontents and magma ascent rates in controlling eruption styles using petrological, Recently, it has been shown that most volcanoesĪround the globe and particularly in a subduction-setting, are able to produce bothĮffusive and violently explosive eruptions with sometimes rapid transitions betweenĮruption styles in the span of a few hours to minutes. I focus on the Rabaul caldera system (Papua-New-Guinea) where effusive, strombolian, Geochemical, textural and petrophysical methods on fresh volcanic deposits. ![]() Second I use apatite to �finely study the volatile budgets and degassing rates I �find that slightĬhanges in the pre-eruptive state of the magma such as phenocryst-content andĮxsolved volatile contents influenced magma ascent rates and subsequent eruption Vulcanian and sub-plinian eruptions occured in the past 120 years withoutĪny noticeable chemical changes in the magma compositions.
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