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6 - Tephra fall hazard for the Neapolitan area
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- By W. Marzocchi, Istituto Nazionale di Geofisica e Vulcanologia, Italy, J. Selva, Istituto Nazionale di Geofisica e Vulcanologia, Italy, A. Costa, Istituto Nazionale di Geofisica e Vulcanologia, Italy, L. Sandri, Istituto Nazionale di Geofisica e Vulcanologia, Italy, R. Tonini, Istituto Nazionale di Geofisica e Vulcanologia, Italy, G. Macedonio, Istituto Nazionale di Geofisica e Vulcanologia, Italy
- Edited by Susan C. Loughlin, Steve Sparks, University of Bristol, Sarah K. Brown, University of Bristol, Susanna F. Jenkins, University of Bristol, Charlotte Vye-Brown
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- Book:
- Global Volcanic Hazards and Risk
- Published online:
- 05 August 2015
- Print publication:
- 24 July 2015, pp 239-248
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- Chapter
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Summary
The Neapolitan area is one of the highest volcanic risk areas in the world, both for the presence of three potentially explosive and active volcanoes (Vesuvius, Campi Flegrei and Ischia), and for the extremely high exposure (over a million people located in a very large and important metropolitan area). Even though pyroclastic flows and lahars represent the most destructive phenomena near the volcanoes, tephra fall poses a serious threat on a wider spatial scale. Excess of tephra loading can cause building collapse, disrupt services and lifelines, and severely affect agriculture and human health. On a larger spatial scale, tephra fallout may cause a major disruption of the economy in Europe and in the Mediterranean area (Folch & Sulpizio, 2010, Sulpizio et al., 2012).
The volcanic hazard is the way in which scientists quantify such a kind of threat. The hazard is usually expressed in probabilistic terms in order to account for the vast irreducible (aleatory) and reducible (epistemic) uncertainties. In the past several papers focussed on the assessment of tephra fallout hazard from Neapolitan volcanoes (e.g. Barberi et al. (1990), Macedonio et al. (1990), Cioni et al. (2003), Costa et al. (2009)). These studies have combined field data of tephra deposits and numerical simulations of tephra dispersal (often considering tens of thousands of wind profiles to account for wind variability) to produce maps for the expected tephra loading in case of a specific scenario (e.g. considering one specific kind of eruption), or of a few reference scenarios at both Mount Vesuvius and Campi Flegrei.
This kind of map is still frequently used in volcanology, however, they do not represent the real volcanic hazard, because they do not consider the probability of occurrence of the specific scenarios considered, and they neglect a large part of the natural variability, such as the possibility to have eruptions of different size and from different vents. The latter is particularly important for the Campi Flegrei caldera, where the largest source of uncertainty comes from the forecast of the next eruption location. From a more technical point of view, these studies do not properly incorporate all known aleatory and epistemic uncertainties. This aspect is of primary importance in order to get a reliable volcanic hazard assessment.
Viscous heating effects in fluids with temperature-dependent viscosity: triggering of secondary flows
- A. COSTA, G. MACEDONIO
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- Journal:
- Journal of Fluid Mechanics / Volume 540 / 10 October 2005
- Published online by Cambridge University Press:
- 27 September 2005, pp. 21-38
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Viscous heating can play an important role in the dynamics of fluids with a strongly temperature-dependent viscosity because of the coupling between the energy and momentum equations. The heat generated by viscous friction produces a local increase in temperature near the tube walls with a consequent decrease of the viscosity and a strong stratification in the viscosity profile which can trigger instabilities and a transition to secondary flows.
In this paper we present two separate theoretical models: a linear stability analysis and a direct numerical simulation (DNS) of a plane channel flow. In particular DNS shows that, in certain regimes, viscous heating can trigger and sustain a particular class of secondary rotational flows which appear organized into coherent structures similar to roller vortices. This phenomenon can play a very important role in the dynamics of magma flows and, to our knowledge, it is the first time that it has been investigated by a direct numerical simulation.