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Volcanic hazard and risk assessment in a multi-source volcanic area: the example of Napoli city (Southern Italy)
Full text linkThe possible emplacement of pyroclastic fall and flow products from Campi Flegrei and Somma-Vesuvio represents a threat for the population living in Napoli city. For this area, the volcanic hazard was always partially investigated to define the hazard related to the Campi Flegrei or to the Somma-Vesuvio activity one at a time. A new volcanic hazard and risk assessment, at the municipality scale, as a vital tool for decision-making about territorial management and future planning, is presented here. <br><br> In order to assess the hazard related to the explosive activity of both sources, we integrated the results of field studies and numerical simulations, to evaluate the future possibility for Napoli to be hit by the products of an explosive eruption. This is defined for the Somma Vesuvio central volcano through the sum of "field frequency" based on the thickness and distribution of past deposits (Lirer et al., 2001), and for the Campi Flegrei volcanic field by suitably processing simulated events based on numerical modelling (Alberico et al., 2002; Costa et al., 2009). Aiming at volcanic risk assessment, the hazard areas were joined with the exposure map, considered for our purposes as the economical value of artefacts exposed to hazard. We defined four risk classes, and argued that the medium and low-very low risk classes have the largest extent in Napoli municipality, whereas only few zones located in the eastern part of the city and in the westernmost coastal area show a high risk, owing to the correspondence of high economical value and high hazard
THE OTTAVIANO ERUPTION OF SOMMA-VESUVIO (8000 y B.P.): A MAGMATIC ALTERNATING FALL AND FLOW-FORMING ERUPTION.
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Transient Fluidization and Segregation of Binary Mixtures of Particles
No full textFluidization of binary mixtures of particles belonging to group B of the Geldart classification of powders was studied. Beds tested were prepared by mixing in the different proportions particles with almost equal density (approximate to2,500 kg/m(3)) and dissimilar size (125 mum silica sand and 500 mum glass beads). Experiments were carried out using a segmented fluidization column equipped with multiple pressure transducers. Experimental procedures included continuous monitoring of pressure drop at different locations along the bed during quasi-steady or stepwise changes of gas superficial velocity, and characterization of particle-size distributions in each segment of the fluidization column after fluidization of the bed for given times. Three ranges of gas superficial velocity were recognized for each solids mixture. At low velocity the bed behaves as a fixed bed. At high velocity, it is fully and steadily fluidized. In an intermediate velocity range, transient fluidization takes place: an initially uniform fluidized bed eventually undergoes segregation, giving rise to a defluidized bottom layer rich in the coarser solids and to a "supernatant" fluidized layer where finer particles prevail. The thresholds between these velocity ranges are rather sharp and were characterized as functions of initial bed composition. Rates at which the defluidized solids layer builds up from initially uniform beds, and the ultimate compositions of the defluidized bottom and fluidized top layers are characterized for beds with different compositions at variable gas superficial velocity
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