Semi-automatic procedure for the characterization of the shape of volcanic particles

Volcanic ash is composed of different components, namely juvenile particles, lithics and crystals. Quantifying the relative percentage of the component typologies forming an ash sample is a very important tool to better investigate the physical and geochemical processes related to the dynamics of an explosive event. Such a goal is further enhanced when associated to the characterization of the morphology of volcanic ash particles. However, the measurement and quantification of particle shape are hard challenges, especially when the number of the particles to analyse is high and the size small (i.e. sub-millimetric), as in the case of volcanic ash. The methods for quantitative measurements of particle shape currently used in volcanology are based on image processing, mainly achieved by manual outputs (e.g. microscopy investigations), techniques which are usually time consuming and meticulous permitting to analyse only a limited number of particles. Here we present preliminary results of a new procedure aimed to the development of a fast and reliable, semi-automatic technique for the characterization of morphological and dimensional parameters of a given volcanic ash sample. The proposed procedure founds on the results deriving from CAMSIZER, a compact laboratory instrument developed by Retsch Technology (see http://retsch-technology.com) for the simultaneous measurement of particle size distribution and particle shape of incoherent materials in the range of 30 µm to 30 mm. CAMSIZER bases on digital image processing and permits to obtain measurements of shape parameters on a high number of particles. Our procedure provides first the measurement of the ash sample by CAMSIZER. The obtained results are successively used as input data in cluster analysis model that bases on fuzzy c-mean algorithm, allowing us to semi-automatically define the main classes grouping all those particles characterized by similar morphological parameters. The prospective on the potential of such a combined methodology is primarily a better, faster and reliable characterization of the ash erupted from diverse eruptions in order to infer the different explosive styles. Secondarily, considering that the shape parameters of volcanic ash particles are crucial input data for most of the recent numerical models simulating plume dispersal in atmosphere and tephra fallout on ground, future applications of the procedure seem to be promising for the prompt actions to perform during the routine monitoring activity of active volcanoes and for the improvement of plume dispersion models.