Image processing of explosive activity at Stromboli

Abstract

A new way to study the dynamics of explosive behaviour at different vents of Stromboli volcano is proposed. The method is based on computer processing of images taken by an infrared film camera, at a rate of 4 pictures per second. Each picture has been digitized by use of an image scanner with a 75 d.p.i. (dots per inch) resolution and 256 levels of gray, then processed and the total mass of the ejected material has been calculated for each photograph. With this procedure the flux of ejected matter throughout every single explosive event has been reconstructed. The analysis of trajectories made on adequate samples of ejecta has allowed us to evaluate the ejection velocity. The mode of the mass flux distribution and the mean value of the velocities calculated for individual particles quantify the kinetic energy of an explosion. Vents nos. 1 and 3, which remained active after the last effusive eruption of 1985–1986, show several explosive patterns, the energy of which is measured. The observed flux distributions have been checked both numerically and experimentally by modelling impulsive events. The computer simulations of the mass distributions have allowed us to speculate on the possible explosive dynamisms. Two different models have been used: a single impulse model confirms the behaviour actually shown by one of the two vents, while the behaviour of the other is better depicted by a cumulative trend of successive impulses in rhythmic sequence. Moreover, through the experimental approach we have had the opportunity to test the overall resolution of the method. The observed matter flux distribution has then been associated to the seismic signals in order to correlate the dynamics involved in the explosions with the seismic source mechanisms.