Flank Cones at Mount Etna Volcano: Do they have a power-law distribution?

Abstract.

Mount Etna is currently characterised by intense effusive and explosive activity of its summit vents, whereas 319 non-active Holocene flank cones are spread across its flanks at altitudes of between 2990 and 475 m. In volcanic areas the relationships between fracture occurrence and cone growth/location are well established. With this in mind, the spatial distribution of the Mount Etna flank cones was analysed in order to make some inferences about the fracture systems that feed the cones. The positions of the flank cones were acquired by the use of a digital elevation model of the volcano with a geometric resolution of 10×10 m. Spatial distribution of the cones was analysed through counting-box and sand-box methods, checking for fractal or multifractal behaviours. The four data sets analysed consist of the whole number of parasitic cones (319), and cones located on the NE (50), south (143) and west (61) rifts, respectively. The cones have a non-trivial power-law distribution. The sand-box method gave the best results with a fractal exponent D_f for all cones of 1.41±0.02 over the length range 0.2–10 km. The same analysis was performed on the other data sets: South Rift (1.42±0.02); West Rift (1.39±0.02); and NE Rift (1.43±0.02). The cones do not have a multifractal distribution, as suggested also by the strong similarity between fractal exponents of the different data sets. Data suggest a strong control over flank cone distribution by fracture length and density. These two characteristics are, in turn, expressions of highly connected fractures activated as magma feeders by the volcano's present stress field. We interpret the rifts as inherited structures that represent preferential sites of fracture connectivity.