CRISCI G.M. (1); IOVINE G. (2); DI GREGORIO S. (3); V. LUPIANO (1), 2008, Lava-flow hazard on the SE flank of Mt Etna (Southern Italy), Journal of volcanology and geothermal research 177 (2008): 778–796. doi_10.1016/j.jvolgeores.2008.01.041,
URL: http://www.cnr.it/prodotto/i/168892

A method for mapping lava-flow hazard on the SE flank of Mt. Etna (Sicily, Southern Italy) by applying the Cellular Automata model SCIARA-fv is described, together with employed techniques of calibration and validation through a parallel Genetic Algorithm. The study area is partly urbanised; it has repeatedly been affected by lava flows from flank eruptions in historical time, and shows evidence of a dominant SSE-trending fracture system. Moreover, a dormant deep-seated gravitational deformation, associated with a larger volcano-tectonic phenomenon, affects the whole south-eastern flank of the volcano. The Etnean 2001 Mt. Calcarazzi lava-flow event has been selected for model calibration, while validation has been performed by considering the 2002 Linguaglossa and the 1991-93 Valle del Bove events -- suitable data for back analysis being available for these recent eruptions. Quantitative evaluation of the simulations, with respect to the real events, has been performed by means of a couple of fitness functions, which consider either the areas affected by the lava flows, or areas and eruption duration. Sensitivity analyses are in progress for thoroughly evaluating the role of parameters, topographic input data, and mesh geometry on model performance; though, preliminary results have already given encouraging responses on model robustness. In order to evaluate lava-flow hazard in the study area, a regular grid of n.340 possible vents, uniformly covering the study area and located at 500 m intervals, has been hypothesised. For each vent, a statisticallysignificant number of simulations has been planned, by adopting combinations of durations, lava volumes, and effusion-rate functions, selected by considering available volcanological data. Performed simulations have been stored in a GIS environment for successive analyses and map elaboration. Probabilities of activation, empirically based on past behaviour of the volcano, can be assigned to each vent of the grid, by considering its elevation, location with respect to the volcanic edifice, and proximity to its main weakness zones. Similarly, different probabilities can be assigned to the simulated event types (combinations of durations and lava volumes, and to the effusion-rate functions considered). In such a way, an implicit assumption is made that the volcanic style will not dramatically change in the near future. Depending on adopted criteria for probability evaluation, different maps of lava-flow hazard can be compiled, by taking into account both the overlapping of the simulated lava flows and their assumed probabilities, and by finally ranking computed values into few relative classes. The adopted methodology allows to rapidly exploring changes in lava-flow hazard as a function of varying probabilities of occurrence, by simply re-processing the database of the simulations stored in the GIS. For Civil Protection purposes, in case of expected imminent opening of a vent in a given sector of the volcano, reprocessing may help in real-time forecasting the presumable affected areas, and thus in better managing the eruptive crisis. Moreover, further simulations can be added to the GIS data base at any time new different event types were recognised to be of interest. In this paper, three examples of maps of lava-flow hazard for the SEflank of Mt. Etna are presented_ the first has been realised without assigning any probability to the performed simulations, by simply counting the frequencies of lava flows affecting each site; in the second map, information on past eruptions is taken into account, and probabilities are empirically attributed to each simulation based on location of vents and types of eruption; in the third one, a stronger role is ascribed to the main SSE-trending weakness zone, which crosses the study area between Nicolosi and Trecastagni, associated with the right flank of the above-cited deep-seated deformation. Despite being only preliminary (as based on a sub-set of the overall planned simulations), the maps clearly depict the most hazardous sectors of the volcano, which have been identified by applying the coupled modelling-GIS method here described.

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